Publish Year: 2021 Title: Unique Non-Bead Cultured Freshwater Pearls from Lake Biwa, Cultured for 14 Years Abstract: Figure 1. The two Biwa pearl samples that were cultured for 14 years and acquired from Jinbo Pearls, measuring 19.75 × 10.38 × 9.84 mm (pearl A, left) and 23.48 × 12.36 × 11.08 mm (pearl B, right). Photo by Shunsuke Nagai.

Lake Biwa in Shiga Prefecture has been producing pearls since 1928, when commercial freshwater pearl culturing first started in Japan. Although production decreased in the late twentieth century due to environmental issues and the declining mussel population (S. Akamatsu et al., “The current status of Chinese freshwater cultured pearls,” Summer 2001 G&G, pp. 97–113), Biwa pearls harvested in the twenty-first century, as well as vintage ones, are popular in the Japanese market. Hyriopsis schlegelii, an indigenous freshwater mollusk found in the lake prior to the 1980s, was originally used as the host for pearl culturing before it was replaced by the hybrid Hyriopsis schlegelii × Hyriopsis cumingii freshwater mollusk.

Figure 2. Left: Macro images of pearls A and B. Photos by Nanthaporn Nilpetploy. Center and right: The internal structures as revealed by RTX and μ-CT analysis, respectively.
GIA’s Tokyo laboratory received for study 28 pearl samples with a stated Biwa provenance from Jinbo Pearls, a Shiga-based company that deals exclusively with freshwater pearls from Lake Biwa. Two of the largest samples (figure 1), weighing and measuring 16.08 ct, 19.75 × 10.38 × 9.84 mm (pearl A) and 22.85 ct, 23.48 × 12.36 × 11.08 mm (pearl B), respectively (figure 2, left), were selected for further detailed study. The intriguing fact was that they were reportedly grown over a period of 14 years—from 2002 to 2016. This is an unusually long growth period, since freshwater non-bead cultured (NBC) pearls normally take three years to form in Japanese farms. However, the farm where these samples originated was abandoned by the owner due to personal issues. Remarkably, several mussels were found alive when the farm was rechecked before being officially closed by the owner’s relatives in 2016. These two pearls were collected from two of the surviving mussels.

Figure 3. The fluorescence reactions of both pearl samples under optical X-ray fluorescence. The pearls prior to sawing (A-1, B-1) showed strong yellowish green reactions, with some weak yellowish orange areas within some imperfections around their circumference (white arrows, A-2, B-2). The sawn pearls (A-3, B-3) showed strong yellowish green reactions, with stronger reddish orange areas in some positions (A-4, B-4). Images by Kwanreun Lawanwong.
Real-time microradiography (RTX) examination revealed a faint linear feature along the length of each pearl (figure 2, center). X-ray computed microtomography (µ-CT) analysis showed these features more clearly and revealed an additional small dark void at the end of pearl A’s linear structure (figure 2, right). Their internal structures corresponded well to other non-bead cultured freshwater pearls described in previous studies (M.S. Krzemnicki et al., “X-ray computed microtomography: Distinguishing natural pearls from beaded and non-beaded cultured pearls,” Summer 2010 G&G, pp. 128–134). Additionally, optical X-ray fluorescence analysis showed a strong yellowish green reaction with weak yellowish orange areas within some imperfections around the circumference of the pearls (indicated by white arrows, figure 3, A-2 and B-2).
Each pearl was cut in half (cut surfaces were cleaned with isopropyl alcohol) and the examination results were compared with those obtained prior to sawing. Surprisingly, both showed stronger reddish orange optical X-ray fluorescence reactions within small areas along the central structure lines (RTX and μ-CT analysis) visible on each sawn face (figure 3, A-4 and B-4) than on any external surface areas when the pearls were intact. Such reactions are sometimes seen in natural and freshwater cultured pearls (Summer 2013 Lab Notes, pp. 113–114; Spring 2019 Lab Notes, pp. 94–96; S. Karampelas et al., “Chemical characteristics of freshwater and saltwater natural and cultured pearls from different bivalves,” Minerals, Vol. 9, No. 6, 2019, article no. 357, pp. 16–17).

Figure 4. Photomicrographs of the cross sections showing some dull white frosty surfaces (black arrows, A-3, B-3) that correspond to the areas showing reddish orange fluorescent reactions under optical X-ray fluorescence. Field of view 19.20 mm (A-1, B-1), 14.40 mm (A-2, B-2), and 2.88 mm (A-3, B-3). Photos by Kwanreun Lawanwong.
It was especially interesting that the reactions seemed to correlate with the dull frosty white surface areas along the central structure lines on the sawn-faces when observed under the microscope at higher magnifications (indicated by black arrows in figure 4, A-3 and B-3). This observation was consistent with previous studies on freshwater cultured pearls (Spring 2019 Lab Notes, pp. 94–96).
Raman analysis of these areas showed they consisted of two CaCO3 polymorphs: aragonite and vaterite. Aragonite features were visible at 701, 704, and 1085 cm–1, while vaterite features were noted at 740, 750, 1075, and 1090 cm–1. Aragonite and vaterite in cultured FW pearls have previously been recorded (U. Wehrmeister et al., “Vaterite in freshwater cultured pearls from China and Japan,” Journal of Gemmology, Vol. 30, No. 7/8, 2007, pp. 399–412; A.L. Soldati et al., “Structural characterization and chemical composition of aragonite and vaterite in freshwater cultured pearls,” Mineralogical Magazine, Vol. 72, No. 2, 2008, pp. 579–592; H. Ma et al., “Vaterite or aragonite observed in the prismatic layer of freshwater-cultured pearls from South China,” Progress in Natural Science, Vol. 19, No. 7, 2009, pp. 817–820). Furthermore, calcite was also detected in pearl A, where peaks at 280, 714, and 1085 cm–1 were observed. The first two peaks were isolated and did not appear in association with any other peaks (groupings or doublets), proving they were another CaCO3 polymorph. Up until recently, calcite had not been reported in freshwater cultured pearls, though it was found in a small area of pearl A in this study and was also noted in a pearl discussed in a recent study (S. Eaton-Magaña et al., “Raman and photoluminescence mapping of gem materials,” Minerals, Vol. 11, No. 2, 2021, article no. 177, pp. 24–27).
Further advanced analysis of the cross sections’ trace element concentrations was conducted using laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). The reddish orange fluorescent areas were shown to contain much higher Mg (1250 ppmw for pearl A and 2260 ppmw for pearl B) and lower Na (1210 ppmw for pearl A and 1310 ppmw for pearl B) concentrations than other areas of the samples not exhibiting the reaction (Mg lower than 77 ppmw and Na higher than 1930 ppmw). This result is consistent with those detailed in the literature (Soldati et al., 2008; Eaton-Magaña et al., 2021). The results seemed to correspond with the Raman data, and the different Mg and Na ratios helped to separate aragonite and vaterite, though it is difficult to differentiate calcite from either without performing Raman analysis.
Vaterite within the structure of NBC FW pearls is thought to be related to the biomineralization process that results following the tissue/mantle insertion (Wehrmeister et al., 2007), and its presence is a strong indicator of a cultured origin. These two unique pearls are a part of 28 Biwa pearl samples collected over various time frames. Since they are worthy of being singled out for discussion, this brief report is a precursor to a more detailed review of both pearls and the other Biwa pearl samples referenced. @topic:5


Publish Year: - Title: A Study on Improving the Surface Appearance of Low-Quality Pinctada maxima Bead Cultured Pearls Abstract: Five low-quality Pinctada maxima bead cultured pearls showing dull surface lusters, yellowish brown imperfections, and residual organic-rich features. Photo: Nuttapol Kitdee

Pearls are evaluated based on seven value factors, which include size, shape, color, luster, surface, nacre quality, and matching. Manufacturers often increase the perceived value of low-quality pearls by improving the appearance of one or more of these factors. In this study, the Bangkok laboratory examined five low-quality bead cultured pearls sourced directly from a local pearl factory and characterized their features before and after processing. Real-time microradiography (RTX), energy dispersive X-ray fluorescence (EDXRF), and Raman spectroscopy were utilized to check potential differences in nacre thicknesses, fluorescence reactions, and chemical and mineral compositions.

The results are available in a study titled “A Study on Improving the Surface Appearance of Low-Quality Pinctada maxima Bead Cultured Pearls.” The authors concluded that methods used to improve the appearance of low-quality pearls were not always successful, and the level of success might not be economically viable for manufacturers. @topic:5


Publish Year: - Title: Spring 2019 G&G: Tourmaline Classification, Provenance of Freshwater Pearls, and the Annual Tucson Report Abstract: Color is king in the new issue of Gems & Gemology. From the variety of colors found in the 33 known species of tourmaline to the diverse goods seen at the Tucson gem shows, our Spring 2019 issue is a testament to the trade popularity and scientific relevance of colored gemstones. The issue also includes an article on the gemological characteristics of the Talisman of Charlemagne; provenance studies on freshwater pearls from the U.S. and China using LA-ICP-MS and LDA; the impact of cut and orientation of table facets on the color-effect in alexandrite; and a field report from the sapphire, opal, and emerald deposits of Ethiopia.
A New Method for Determining Gem Tourmaline Species by LA-ICP-MS
Gem-grade tourmaline comes in a wide variety of colors and species, from elbaite to dravite to liddicoatite. In our lead article, Ziyin Sun, Aaron C. Palke, Christopher M. Breeding, and Barbara Dutrow present a classification scheme for tourmaline that uses laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) to collect quantitative measurements of major, minor, and trace elements. These measurements allow gemological laboratories to determine tourmaline species with good precision and accuracy.
U-Pb Ages of Zircon Inclusions in Sapphires from Ratnapura and Balangoda (Sri Lanka) and Implications for Geographic Origin
Zircon is able to withstand peak temperatures but also survive post-cooling conditions. Due to these properties, when found as inclusions in sapphire, zircon is able to provide geological insight into the secondary deposits from which the host sapphires formed. A team led by Emilie Elmaleh and Susanne Theodora Schmidt investigates zircon inclusions in sapphires from two Sri Lankan deposits. Through spectroscopic methods, trace-element chemistry, and U-Pb dating the authors establish a metamorphic/metasomatic, non-basalt-related origin for these sapphires.
The Talisman of Charlemagne: New Historical and Gemological Discoveries
Housed at the Palace of Tau Museum in Reims, France, the Talisman of Charlemagne is an opulent artifact from the Middle Ages that has been said at various times to contain both hair of the Virgin Mary and pieces of the True Cross. It has been linked with Charlemagne, Napoleon, and several other historical figures. The first gemological study of the piece was recently performed at the museum with portable equipment by Gerard Panczer and his coauthors. Based on their findings and comparison with other pieces from the period, the authors were able to propose origins for the sapphire, garnets, and emeralds used in the talisman.
Provenance Discrimination of Freshwater Pearls by LA-ICP-MS and Linear Discriminant Analysis (LDA)
Some non-bead-cultured (NBC) freshwater pearls can be challenging to identify, as their growth features may be similar to those found in some naturally occurring pearls. Using LA-ICP-MS and linear discriminant analysis (LDA), Artitaya Homkrajae, Ziyin Sun, Troy Blodgett, and Chunhui Zhou were able to pinpoint a method that identifies the growth environment of freshwater pearls with greater confidence.
Pleochroism and Color Change in Faceted Alexandrite: Influence of Cut and Sample Orientation
The color appearance of faceted alexandrites results in large part from the gem’s pleochroism, but it may also be influenced by trace-element content, cut, size, and other factors. Using samples cut from synthetic crystals, Karl Schmetzer investigates the color appearance of faceted alexandrite. He documents the impact of the inevitable multiple internal reflections on placement of this biaxial gem’s table facet, as well as its perceived color change and pleochroism.
Land of Origins: A Gemological Expedition to Ethiopia
In the past decade, Ethiopia has become known as a source of opal, sapphire, and emerald. In 2018, a field expedition led by Wim Vertriest explored the various gem deposits of Ethiopia. While there, the team visited mines and markets, documented methods of mining, and experienced the cultures of the different regions of this remarkable country.
Lab Notes
Notable examinations by GIA laboratory staff around the world include the largest diamond ever mined in North America, a color-change sapphire from Myanmar (formerly Burma), and the largest gahnospinel seen by GIA.
Diamonds from the Deep
In our newest section, Karen Smit and Steven Shirey explore the ages of natural diamonds and the impact they have on the world around us. They discuss how diamond formation is linked to plate tectonic processes, as well as how elements are recycled in the deep earth.
Micro-World
G&G’s section on inclusions and photomicrography highlights grandidierite inclusions in sapphires, a fossil insect in a free-form opal, and copper inclusions in a purple chalcedony from Indonesia.
Gem News International
Our annual Tucson report features colored stone market trends, the work of designers such as Derek Katzenbach and Paula Crevoshay, and trade involvement in the responsible sourcing of gemstones “Sourcing Stones with Columbia Gem House”. Non-Tucson Gem News entries focus on sapphires “Sapphires from Colombia” and trapiche emerald  “Trapiche emerald from Colombia”, both from Colombia, and CIBJO’s new responsible sourcing Blue Book.
The Spring issue also contains the 2017 Gems & Gemology Challenge. Score 75% or better and you’ll receive a certificate of completion (PDF file); earn a perfect score and your name will be listed in the Fall 2019 issue. Mail-in cards and online entries for the Challenge must be submitted by Monday, August 12, 2019. @topic:2


Publish Year: - Title: Summer 2019 G&G: Mozambican Ruby, Challenges in Pearl Identification, and an Opal Inclusions Chart Abstract: The Summer 2019 edition of Gems & Gemology opens with a look at the past decade of ruby production in Mozambique, now the world’s leading supplier. The issue also features an investigation into low-temperature heat treatment of Madagascar sapphire, information on a source of black nephrite in southern China, a pair of pearl studies, and an opal inclusions chart.
A Decade of Ruby from Mozambique: A Review
While gemstones have been known from Mozambique for some time, the country became a major player in the trade after facet-quality ruby was unearthed in Niassa and, more importantly, Montepuez in 2009. In the lead article, Wim Vertriest and Sudarat Saeseaw provide a snapshot of the first decade of Mozambican ruby. The authors review production from the deposits, the characteristics of the rubies, and their impact on the market.
Madagascar Sapphire: Low-Temperature Heat Treatment Experiments
African corundum makes an encore in the second article. Known for its fine blue sapphire, Madagascar also produces specimens that react well to heat treatment at low temperatures to lighten their color. E. Billie Hughes and Rosey Perkins perform heating experiments to separate heated from unheated blue Madagascar sapphires.
Black Nephrite Jade form Guangxi, Southern China
A nephrite deposit in the southern Chinese region of Guangxi, discovered in 2012, has produced black nephrite jade that is popular in the Chinese market. A team of authors led by Qian Zhong study the gemological characteristics of 12 rough nephrite specimens from this locality and find that high iron content is responsible for their color and high refractive index. The authors assert that Guangxi’s nephrite deposits are part of a larger jade formation belt in southern China.
Evidence of Rotation in Flame-Structure Pearls from Bivalves of the Tridacnidae Family
Non-nacreous pearls with flame structures from the Tridacnidae family may exhibit some distinctive properties, including pseudo-chatoyancy as well as spirals and or/blade impeller patterns at the apex or base. Jean-Pierre Gauthier and coauthors examine 37 pearls from the Tridacnidae family to understand their properties and formation. The patterns seem to suggest rotation of the pearls during formation or during the growth phase prior to harvesting.
A Pearl Identification Challenge
Nicholas Sturman and a team from three different research institutes investigate the properties of two pearls that were anything but routine. The researchers were unable to positively identify the pearls’ origin (natural or cultured), their growth environment (freshwater or saltwater), or the producing mollusk.
Inclusions in Natural, Treated, Synthetic, and Imitation Opal
The issue also contains the fifth in G&G’s series of inclusion charts. Nathan Renfro and coauthors present a chart of micro-features in natural, treated, synthetic, and imitation opal.
Lab Notes
GIA laboratory staff members present their latest findings in the Lab Notes section, including a resin-coated and clarity-enhanced aquamarine pendant, a rough diamond coated with fake green “radiation stains,” and a report on a color-change spessartine garnet.
Micro-World
The Micro-World section, dedicated to the inner world of gemstones, features a purple fluorite inclusion in a Russian emerald, a Mexican opal with a large fluid inclusion, and an inclusion-rich black topaz from Utah.
Diamonds from the Deep
In G&G’s newest section, Karen Smit and Steven Shirey look at the relationship between kimberlites and diamonds and provides an understanding of how diamonds travel to the earth’s surface after formation in the mantle.
Gem News International
Finally, GNI correspondents from around the world report on jadeite jade from the Polar Ural Mountains of Russia, rubies from the Rock Creek deposit in Montana, and the leveraging the tagua nut as a sustainable alternative to ivory in jewelry. @topic:9


Publish Year: 2001 Title: Spectral Reflectance and Fluorescence Characteristics of Natural-Color and Heat-Treated “Golden” South Sea Cultured Pearls Abstract: A comparison study was made between the yellow and white nacre of the gold-lipped Pinctada maxima oyster shell and 65 yellow cultured pearls, both natural and treated color, produced from this mollusk. The yellow nacre of this shell has a characteristic absorption feature in the UV region between 330 and 385 nm; the strength of this feature increases as the color becomes more saturated. White shell nacre fluoresces very light blue or very light yellow to long-wave UV radiation, whereas yellow shell nacre fluoresces greenish to brownish yellow or brown. Natural-color yellow cultured pearls from P. maxima exhibited absorption and fluorescence characteristics similar to those of the yellow shell nacre. In contrast, the absorption feature in the UV was either weak or absent in yellow cultured pearls reportedly produced by a method involving heat treatment, and their fluorescence was generally very light blue or light yellow. @topic:5


Publish Year: 2012 Title: Identification of Irradiated South Sea Cultured Pearls Using Electron Spin Resonance Spectroscopy Abstract: Irradiated South Sea cultured pearls (SSCPs) from the Pinctada maxima mollusk typically show colors from light gray to silver. It is difficult to identify gamma-ray irradiation of SSCPs using standard gemological methods because of their thick nacre. Therefore, an advanced analytical technique such as electron spin resonance (ESR) spectroscopy is needed to detect the treatment. ESR measurements of minute amounts of SSCP powders revealed the formation of CO2-radicals, and the parameter known as the g-factor was measured at 2.0015 ± 0.0005. Higher levels of CO2-radicals were detected in the pearl nacre than in the nucleus. Therefore, the existence of CO2-radicals is an indicator of irradiated SSCPs. @topic:5


Publish Year: 2024 Title: Large CVD-Grown Diamond Resubmitted after HPHT Treatment Abstract: Figure 1. This 15.73 ct G-color CVD-grown diamond showed indications of HPHT treatment. Photo by Jian Xin (Jae) Liao.
In January 2022, the record holder for largest diamond grown by chemical vapor deposition (CVD) was a 16.41 ct square modified brilliant with G color and VVS2 clarity that showed no indications of post-growth treatment (Spring 2022 Lab Notes, pp. 54–56). Recently, this diamond was resubmitted to the Carlsbad laboratory with a weight of 15.73 ct (figure 1). Standard data collection indicated that since the original submission, the stone had undergone high-pressure, high-temperature (HPHT) treatment. Consequently, this provided a case study showing the spectral and fluorescence differences between the as-grown and HPHT-treated versions. The color and clarity grades remained unchanged.
Although HPHT processing of CVD-grown diamonds is often performed to improve the color grade by reducing brown coloration (S. Eaton-Magaña and J.E. Shigley, “Observations on CVD-grown synthetic diamonds: A review,” Fall 2016 G&G, pp. 222–245), the diamond displayed no observable color improvement. It is also likely that the HPHT treatment created frosting of the facets that required repolishing, which could partially account for the 0.68 ct weight loss.

Figure 2. DiamondView fluorescence images collected on the originally submitted CVD-grown diamond (left, from Spring 2022 Lab Notes) exhibited no evidence of post-growth treatment, while the recent submission (right) showed signs of HPHT treatment. Images by Stephanie Persaud (left) and GIA staff (right).

Figure 3. PL spectra collected on the CVD-grown diamond in January 2022 and recently with 514 nm (left) and 457 nm (right) excitation. Diamond Raman lines are scaled as equal, and spectra are offset vertically for clarity.
DiamondView fluorescence imaging showed pronounced differences between the as-grown and treated stages (figure 2). This color change in fluorescence imaging is often seen in HPHT-treated CVD-grown diamonds due to the reduction of nitrogen vacancy (NV) centers (NV0 with zero-phonon line [ZPL] at 575 nm and NV– at 637 nm) and an increase in H3 (NVN0; ZPL at 503.2 nm). The changes in the defect concentrations leading to the differences in the fluorescence colors were also evident in photoluminescence (PL) spectroscopy collected at liquid nitrogen temperature. Figure 3 shows the PL results with 514 and 457 nm excitation for the 16.41 and 15.73 ct stages of the diamond.
With HPHT treatment, there was a decrease in the NV centers and an increase in the silicon vacancy (SiV–) center at 737 nm in the 514 nm PL spectrum. In the 457 nm PL spectrum, the 468 nm peak and 3H peak (ZPL at 503.5 nm) were no longer detected, while features developed at 494.1, 500.4, and 506.2 nm along with the H3 peak at 503.2 nm.

Figure 4. Comparison of the cathodoluminescence images from before HPHT treatment (left, from Spring 2022 Lab Notes) and afterward (right) showed no observable differences. Images by Elina Myagkaya.
As expected with a treated CVD-grown diamond, there were no major changes in many of the growth features. The cathodoluminescence images in figure 4 show no observable differences; the black dots are associated with lattice dislocations. The seven growth interfaces seen in figures 2 and 4 appear unmodified.
This stone allowed for an interesting comparison of a CVD-grown diamond before and after commercial HPHT treatment. @topic:4


Publish Year: 2024 Title: Natural Orange Diamond with Unusual Absorption Features Abstract: Figure 1. A 0.16 ct Fancy Vivid orange pear (left) and 0.23 ct Fancy Intense orange pear (right). Photos by Towfiq Ahmed.

Figure 2. Fancy Vivid orange color distribution with strong zoning related to crystal growth. Photo by A’Dhi Lall.
Orange is a very desirable color for diamond in the gem trade. GIA’s New York laboratory received two type Ia (nitrogen-bearing) orange diamonds for colored diamond grading service, one 0.16 ct Fancy Vivid orange and the other 0.23 ct Fancy Intense orange (figure 1). Both diamonds showed orange fluorescence to long-wave and short-wave UV, along with few inclusions (clarity grades of VS2 and VVS1, respectively) and strong color zoning related to crystal growth (figure 2).

Figure 3. Ultraviolet/visible/near-infrared spectra of the Fancy Vivid orange and Fancy Intense orange diamonds are shown with several peaks and bands that combine to create these very rare colors. Spectra are offset vertically for clarity.
This diamond hue is often caused by a broad-band absorption at 480 nm. While the 480 nm band was observed in both diamonds, it was supplemented by the presence of a 525 nm peak and the 550 nm band along with a series of absorption features from ~700 to 780 nm with pronounced peaks at 735, 753, and 769 nm (figure 3). The 830 nm photoluminescence (PL) spectra showed very strong nickel peaks at 883/884 nm, in addition to numerous other PL features (A.M. Zaitsev, Optical Properties of Diamond: A Data Handbook, Springer-Verlag, Berlin, 2001). Thus, the 480 nm band was not the exclusive cause of color. The 550 nm band is the most common cause of color in natural pink diamond but, when present with other color centers, can contribute to many different bodycolors.
The optical defects in these orange diamonds differed from those in diamonds exclusively colored by the 480 nm band (M.Y. Lai et al., “Spectroscopic characterization of diamonds colored by the 480 nm absorption band,” Diamond and Related Materials, Vol. 142, 2024, p. 110825). The combination of an unusual absorption band in the near infrared with the 480 and 550 nm absorption bands creates a transmission window that produces the rich, warm orange hue, devoid of any secondary modifying color. This appears to be a newly identified cause of orange color in diamonds. @topic:4


Publish Year: 2015 Title: LPHT-Annealed Pink CVD Synthetic Diamonds Abstract: Figure 1. Three LPHT-annealed CVD synthetic diamonds: Fancy Deep brownish orangy pink 0.37 ct (top left), Fancy Deep brown-pink 0.31 ct (top middle), and Fancy brown-pink 0.25 ct (top right). Their DiamondView images (bottom row) show orange fluorescence with linear growth striations. Top left and middle photos by Sood Oil (Judy) Chia; top right photo by Jian Xing (Jae) Liao. DiamondView images by Kyaw Soe Moe.

Due to nitrogen vacancy and hydrogen complexes, as-grown CVD synthetic diamonds are usually brown, which are less desirable than other colors. Post-growth treatments such as high-pressure, high-temperature (HPHT) treatment and/or irradiation and annealing, are applied to these synthetics to create attractive colors. In the past, we have reported HPHT-treated and multi-step treated pink CVD synthetics. Recently, the New York lab examined three pink CVD-grown diamonds that were treated with the technique known as low-pressure, high-temperature (LPHT) annealing.

The 0.37 ct rectangle, 0.31 ct rectangle, and 0.25 ct round brilliant were graded as Fancy Deep brownish orangy pink, Fancy Deep brown-pink, and Fancy brown-pink, respectively (figure 1). They were classified as type Ib diamond containing single substitutional nitrogen atoms (Ns0) with absorption bands at 1130 and 1344 cm–1 (figure 2). The 0.37 ct sample contained a VS2-grade feather and a few burn marks on the main facets; otherwise, all three were very “clean.” The DiamondView images showed typical orange fluorescence and linear growth striations, which are caused by uneven uptake of defects along the growth steps (again, see figure 1). The orange fluorescence is usually observed in N-doped CVD synthetics.

Figure 2. These CVD synthetics are classified as type Ib with Ns0 atoms at 1130 and
1344 cm–1 (inset A). The LPHT annealing was revealed by C-H stretching bands, as seen
in inset B. Additional unknown bands were also observed (inset C).
The mid-IR spectra revealed post-growth LPHT annealing treatment. In figure 2, the absorption bands of C-H stretching at 2810, 2870, 2900, 2937, 2948, and 3031 cm–1 are created by LPHT annealing (see Y. Meng et al., “Enhanced optical properties of chemical vapor deposited single crystal diamond by low-pressure/high-temperature annealing,” PNAS, Vol. 105, No. 46, 2008, pp. 17620–17625). They were modified and shifted from the peaks of unstable hydrogenated amorphous carbon complexes and NVH– defects during the annealing process. The 3123 cm–1 (NVH0) band, which is a common defect in as-grown CVD synthetic diamonds and annealed out by HPHT treatment, is present. This defect was detected in LPHT-annealed CVD synthetics (again, see Meng et al., 2008). The 3107 cm–1 (N3VH), which can be created by HPHT annealing in CVD synthetic diamonds, is absent. Positively charged single substitutional nitrogen atoms (Ns+) were detected at 1332 cm–1. Additionally, unknown bands were also detected at 1353, 1362, 1371, 4335, 4523, 4648, 4673, 4727, 4886, and 5218 cm–1. A broad absorption band with absorption maxima at approximately 525 nm and sharp nitrogen-vacancy (N-V) centers at 575 nm (NV0) and 637 nm (NV–) in the visible-NIR spectrum are responsible for pink and orange color components in these samples (figure 3). The vivid orange fluorescence in DiamondView images are also attributed to N-V centers. The H3 center is observed at 503 nm. There are also unknown additional absorption bands at 419.5, 485.8, 495.1, 666.5, 685.4, 711.7, 753.1, 781.4, and 850.3 nm. Very strong N-V centers can be observed in the 514 nm PL spectra.

Figure 3. Absorption maxima at approximately 525 nm and N-V centers are responsible
for the pink color in these samples. The H3 center can be observed, along with many
unknown bands.
HPHT annealing can be achieved at temperatures ranging from 1800–2500°C and pressures greater than 5 GPa. High pressure is required in order to prevent graphitization, especially in natural diamond. In contrast, LPHT annealing is performed at temperatures 1400–2200°C and pressures below 300 torr (3.99 × 10–5 GPa, below atmospheric pressure) (again see Meng et al., 2008). Graphitization became significant above 2200°C. At temperatures above 700°C, vacancies started to move and were trapped at single substitutional nitrogen atoms, creating N-V centers; however, nitrogen atoms become mobile at temperatures above 1700°C, causing the N-V centers to anneal out. Therefore, strong N-V centers (which are much greater than the diamond Raman peak) in the 514 nm PL spectra of these samples suggested that they were annealed at temperatures below 1700°C. Lack of a peak at 3107 cm–1 is also suggestive of an annealing temperature below 1700°C. This upper temperature limit is further supported by presence of a band at 3123 cm–1, which can be annealed out at above 1800°C. Incorporation of H3 center occurs above 1500°C; thus, annealing temperatures for these samples can be proposed as 1500°C < T < 1700°C. According to Meng’s experiment, this temperature range can be correlated with pressure from 150 to 200 torr, with annealing time from 10 to 720 minutes.

Brown as-grown CVD synthetics have been changed to brownish pink by LPHT annealing for 15 minutes by Meng et al. (2008); they were also able to improve colorless CVD-grown diamonds by an average of three color grades. LPHT treatment may have created the attractive pink hue in these samples, although it could not completely eliminate the brown coloration. We expect to encounter more LPHT-treated diamonds in the future. @topic:4


Publish Year: 2015 Title: Rare Type IIb Gray-Purple Diamond Abstract: Figure 1. This 1.42 ct type IIb natural diamond was significant for its unusual Fancy gray-purple color and its strong emission at 776.4 nm under PL spectroscopy. Photo by Robison McMurtry.

Photoluminescence (PL) spectroscopy using several laser excitations has become the most important method for determining diamond color origin. Part of PL analysis is observing peaks that correlate with a diamond’s color, type, or other gemological properties, but for which the physical model is still unknown. One such center is the PL peak at 776.4 nm, which is commonly observed in type IIb diamonds with intensely colored (i.e., Fancy to Fancy Deep) blue to gray color and in combination with red phosphorescence (S. Eaton-Magaña and R. Lu, “Phosphorescence in type IIb diamonds,” Diamond and Related Materials, Vol. 20, No. 7, 2011, pp. 983–989). Recently, the Carlsbad laboratory tested a 1.42 ct colored diamond that showed an extremely strong 776.4 nm emission. Infrared absorption spectroscopy confirmed the specimen as a type IIb natural diamond with a boron concentration of approximately 28 ppb. This stone was notable not only for this intense emission, but also for its Fancy gray-purple color (figure 1). This is an extremely rare combination in a type IIb diamond.

Type IIb diamonds sometimes have a violet color description, but they rarely exhibit hues that are outside the blue-gray-violet range. While the perceived difference between a violet and purple diamond may be quite subtle, it is an important distinction when determining color origin. An additional reddish component that distinguishes purple from violet diamonds is extremely rare among type IIb fancy color diamonds. Other type IIb hues include gray-green or yellowish green (e.g., Summer 2009 Lab Notes, p. 136; Spring 2012 Lab Notes, pp. 47–48). Purple diamonds are quite rare and almost exclusively type Ia, their color deriving from the 550 nm band observed in their visible absorption spectra (S. V. Titkov et al., “Natural-color purple diamonds from Siberia,” Spring 2008 G&G, pp. 56–64). This absorption band is also the cause of color for many pink to red diamonds; however, the absorption spectrum for this diamond was featureless within the visible range, which is typical for type IIb diamonds. This stone is likely the first purple type IIb diamond examined at GIA.

Figure 2. With 514 nm excitation and liquid-nitrogen temperatures, the 776 nm PL peak
dwarfs the diamond Raman peak at 552.4 nm and all other PL features in the spectrum.
The intensity ratio between the 776 nm peak and the diamond Raman peak is about 42:1.
The diamond had the strongest 776.4 nm PL emission yet observed by the author (figure 2). The configuration of the optical center is unknown but might include a boron-vacancy complex (T. Ardon and S. Eaton-Magaña, “Spatial distribution of boron and PL optical centers in type IIb diamond,” 2013 GSA Annual Meeting). Red phosphorescence, centered at 660 nm, was observed using DiamondView and excited by both ultraviolet and visible-light wavelengths using fluorescence spectroscopy. The 776.4 nm PL peak is observed when the diamond is at liquid-nitrogen temperatures, but it is outside the visible range and not excited at room temperature. Therefore, this near-infrared emission, while strong, does not contribute to the color of the diamond. The diamond’s red phosphorescence, while subtle, may have been sufficient to introduce enough reddish component to render a purple color call (as opposed to the more common blue to violet). The singular occurrence of the very strong 776.4 nm PL peak and an unusual bodycolor for a type IIb diamond make this stone notable. @topic:4


Publish Year: 2018 Title: Large HPHT-Treated Blue Type IIb Diamond Abstract: Figure 1. This 17.09 ct HPHT-treated blue diamond (left) has ragged-looking graphitization around an inclusion (center, field of view 0.76 mm) and high-order interference colors when viewed with crossed polarizing filters (right, field of view 7.19 mm). Photos by Jian Xin (Jae) Liao (left) and Evan Smith (center and right).
Over the past two decades, high-pressure, high-temperature (HPHT) treatment has emerged as a prominent technology for changing the color of diamonds. It is best known for removing brown coloration from natural type IIa material to yield colorless or, rarely, pink diamonds. Similarly, HPHT treatment can be used to reduce the brown color component of gray or brownish natural type IIb (boron-bearing) diamonds, thereby increasing the underlying blue color. Improvements to equipment and methods continue to push the capabilities of HPHT processing.
GIA’s New York lab recently encountered a notably large HPHT-treated Fancy Intense blue oval-cut diamond (figure 1, left). At 17.09 ct, this is the largest HPHT-treated blue diamond graded by GIA to date. For comparison, the average size of most submitted HPHT-processed blue diamonds lies in the 1 to 5 ct range. HPHT treatment can be challenging to detect with standard gemological tools, but in this case the ragged-looking graphitization around an inclusion and the appearance of moderate to high-order interference colors under crossed polarizers were helpful clues (figure 1, center and right). Advanced testing methods (e.g., infrared spectroscopy and photoluminescence spectroscopy) confirmed that the stone was HPHT treated.

Figure 2. Color zonation (left) becomes more noticeable when viewed through the pavilion. The stronger blue-colored region corresponds with bright greenish blue fluorescence in the DiamondView (right, field of view 5.8 mm). Note that the DiamondView image is taken from the opposite side of the diamond. Images by Evan Smith.
Additionally, this diamond had a striking blue color zonation (figure 2, left) that is thought to be unrelated to HPHT treatment. A region of strong blue color is separated from an almost colorless region by a sharp division with octahedral plane {111} orientation. Color zonation is not uncommon in natural type IIb diamonds, though it is seldom so sharp and planar (J.M. King et al., “Characterizing natural-color type IIb blue diamonds,” Winter 1998 G&G, pp. 246–268). The stronger blue region likely contains more uncompensated boron. It also exhibits more intense greenish blue fluorescence/phosphorescence in DiamondView images (figure 2, right). The color boundary might reflect a change in defect incorporation during diamond growth. @topic:4


Publish Year: 2023 Title: Artisanal Diamond Mining: Addressing the Knowledge Gap Abstract: Figure 1. Artisanal mining in Liberia. Courtesy of Diamonds for Peace.
In the developed world, the word diamond immediately evokes the allure and sparkle of a polished brilliant. What does the word mean, however, for an artisanal diamond miner living in poverty?
Artisanal diamond mining accounts for 20% of global production and significantly impacts millions of lives in the developing world, particularly in Africa. “Artisanal” simply implies that the tools and equipment used by the miners are rudimentary. This type of mining is conducted predominantly by individuals, small groups, or families, who frequently migrate in search of the next deposit. The work is subsistence labor, and the miners typically sell to anyone willing to buy (often without the luxury of a legal transaction). Despite its numerous challenges, which also include smuggling and human rights abuses, artisanal mining is their principal form of income. But beyond the fact that diamonds can be exchanged for subsistence money, what do these miners know about them?
In many countries where artisanal mining is prevalent, miners often have an innate and comprehensive understanding of the material. For example, Sri Lankan gem miners can expertly locate and sort through the illam (gem gravel) and differentiate between the fine-quality and lesser-quality material. They have been doing this for thousands of years. But diamond mining is different, particularly in Africa, where the first known primary deposit was discovered less than 200 years ago. In the twentieth century, the system of grading based on the Four Cs (color, cut, clarity, and carat weight) established a framework for price setting in the diamond trade. This pricing system for polished material underlies the value of rough material and determines its selling price. Therefore, understanding the Four C s is vital to the effective trade of diamond rough.

Figure 2. Miners sorting through gem gravel. Courtesy of Diamonds for Peace.
However, the majority of artisanal miners in Africa do not yet have a strong working knowledge of rough diamond, placing them at a significant disadvantage when negotiating the price of rough with buyers. In 2022, the NGO Diamonds for Peace conducted basic training on rough diamond grading for Liberian miners (figures 1 and 2), a project funded by the World Bank and operating in collaboration with Empowerment Works Incorporated.
Liberia’s first major diamond deposit was discovered in 1957 along the Lofa River, close to the border of Sierra Leone to the north, which has much higher diamond production. Currently, figures stand at around 50,000 carats per annum. Production peaked at 600,000 carats annually in the 1970s (although most of that figure could be attributed to smuggled material coming in from bordering countries). Two civil wars, starting with a military coup in 1980, resulted in export sanctions imposed by the United Nations. Since 2007, when the country joined the Kimberley Process, diamond has been reestablished as an important mineral resource, particularly with the recent discovery of diamond-bearing kimberlites. These deposits have not been commercially exploited. Instead, the mining remains artisanal and the material is found primarily in alluvial placers along the Lofa River.
In pre-training interviews given to establish each miner’s level of knowledge, numerous misconceptions became evident. For instance, they valued a diamond based on carat weight alone, regardless of quality, color, and potential yield. They had also been told that colored diamonds have no value. Such diamond “myths” have disseminated over the past fifty years, and buyers are often quick to exploit the miners’ lack of knowledge.

Figure 3. A parcel of rough diamonds, collected over a month by a Liberian artisanal miner. The diamond indicated by the arrow weighs 0.80 ct. Photo by Beth West.
For artisanal diamond mining to benefit the future of Liberian communities, the diamonds need to be traded for a price that reflects their real-time value according to their potential polished price (figure 3). The diamonds must be fed into the supply chain correctly, and the economic gain needs to find its way back into these rural communities. This boomerang-back of benefit is no easy feat in West Africa.
Yet small steps toward progress can be made by adjusting the information asymmetry. These artisanal miners need to understand the material they are working with. At the very least, it will give them a little more cash in their pocket and a slightly more comfortable standard of living. Regardless of the big picture, a simple win on that level is easily achievable.
Knowledge—and the sharing of it—is the key to building a stronger and more equitable supply chain. It is one thing for the supply chain to be traceable, but quite another for it to be equitable and ethical. To level the playing field, each player must be equally empowered. One thing that allows for such empowerment is knowledge. It is a simple right.
Diamonds for Peace, in collaboration with the author, is currently working on a next-stage “train to teach” program for the miners. @topic:11


Publish Year: 2023 Title: Natural Diamond with Twinning Wisps Resembling a Whale Abstract: This round brilliant diamond displays twinning wisps that resemble a whale. Photomicrograph by Nathan Renfro; field of view 2.62 mm.
The authors recently examined a 0.46 ct type Ia round brilliant diamond with SI1 clarity that had surprisingly patterned twinning wisps. When viewed through the table, the twinning wisps resembled a whale (see above). Twin planes can form in diamond when the orientation of the crystal structure changes during growth in the earth’s mantle. Twinning wisps are atomic defects along this plane, found in ~10% of type Ia diamonds (S. Eaton-Magaña et al., “Natural-color D-to-Z diamonds: A crystal-clear perspective,” Fall 2020 G&G, pp. 318–335).
A termination of one of these features just below the pavilion was examined using photoluminescence (PL) mapping at various excitation wavelengths to examine the distribution of atomic-level defects in the crystal lattice. The PL mapping with 455 nm excitation revealed a relative increase in the defect concentrations of the nitrogen-related centers of H3 (NVN0) with zero-phonon line (ZPL) at 503.2 nm and H4 (4N+2V) with ZPL at 495.9 nm; a weak radiation-related defect, the TR12 with ZPL at 469.9 nm was also detected (A.M. Zaitsev, Optical Properties of Diamond, Springer-Verlag, Berlin and Heidelberg, 2001, and references therein). PL mapping using 633 nm excitation revealed that the GR1 (V0; ZPL at 741.2 nm) had a higher Raman-normalized peak area corresponding to the termination of the twinning wisp compared to diamond adjacent to the wisp. The GR1 defect is typically formed by radiation damage of a diamond lattice. Although the GR1 was elevated, we did not observe radiation stains around the twinning wisps. Furthermore, there were no visible changes to the color of the diamond’s fluorescence when exposed to deep ultraviolet luminescence, which can occur with significant radiation exposure.
This stone offers an example of how natural growth processes in diamond can result in microscopic features that occasionally form delightful patterns. @topic:4


Publish Year: 2023 Title: Inclusion Resembling a Gada in Diamond Abstract: This etch channel seen in the crown facets of a 1.00 ct diamond with SI1 clarity (left) resembled a gada (right), a mace-like weapon wielded by the Hindu god Hanuman. Photomicrograph (left) by Deepak Raj; field of view 0.80 mm. Photo (right) courtesy of the Metropolitan Museum of Art.
Recently, the authors observed an interesting etch channel (see above) in a 1.00 ct L-color type Ia round brilliant diamond with SI1 clarity. It resembled a gada, a mace-like weapon belonging to the Hindu god Hanuman. This etch channel was the only one observed in the diamond; these features are often created by dissolution processes (T. Lu et al., “Observation of etch channels in several natural diamonds,” Diamond and Related Materials, Vol. 10, No. 1, 2001, pp. 68–75).
This unusual clarity characteristic showcases the variety that is possible within the natural world. @topic:4


Publish Year: 2023 Title: Solid Laboratory-Grown Single-Crystal Diamond Ring Abstract: Figure 1. The 4.04 ct ring fashioned from a single-crystal CVD-grown diamond. Photo by Towfiq Ahmed.
Carved single-crystal diamond rings are rare, with few examples to reference (see Spring 2020 Lab Notes, pp. 132–133). But with advancing technology in the laboratory-grown diamond industry, the creation of solid faceted diamond rings is now a reality. Recently submitted to the New York laboratory was a 4.04 ct single-crystal laboratory-grown diamond ring (figure 1). The 3.03 mm thick band had an inner diameter of 16.35–16.40 mm and an outer diameter of 20.32–20.40 mm. The ring was produced by Dutch Diamond Technologies in collaboration with the Belgian jewelry store Heursel, established in 1745.

Figure 2. OpenCV software was used to draw perfect circles from the center of the ring, marked by a green dot. Photo by Towfiq Ahmed.
This laboratory-grown diamond ring was cut from an 8.54 ct plate grown by chemical vapor deposition (CVD). Laser cutting produced a near-perfect circular ring, as demonstrated using digital imaging analysis to measure its inner and outer circumferences (figure 2).
The manufacture of a solid single-crystal diamond ring is a complex and challenging process. Once material is removed from the crystal, very fine fractures and imbalanced strain can have severe consequences, and the ring can shatter. Processing can take more than six months. Creating the ring from a single-crystal laboratory-grown diamond involved about 1,131 hours of processing (including pre-grinding) in the Dutch town of Cuijk, followed by 751 hours of polishing in Belgium.
Infrared absorption analysis revealed it was a type IIa diamond (no detectable nitrogen), and no hydrogen-related peaks were detected at 3107 or 3123 cm–1. Photoluminescence spectroscopy showed interesting vacancy-related defects indicative of a multi-step growth process. A very strong emission from the silicon vacancy (SiV–) defect was observed with 633 nm laser excitation; this is a common feature used to identify CVD-grown diamond. The conclusion was that this ring had not undergone post-growth treatment; nevertheless, it was notable that the ring showed relatively low nitrogen-related defects such as NV centers, along with no detectable 468 nm peak or the 596/597 nm doublet. P. Martineau et al. (“Identification of synthetic diamond grown using chemical vapor deposition (CVD),” Spring 2004 G&G, pp. 2–25) observed the 596/597 doublet with a 514 nm laser. Also of note, there were no H3 or 468 nm centers detected with 457 nm laser excitation.

Figure 3. Strong birefringence observed under cross-polarized light (left) and blue fluorescence observed in the DiamondView (right). Images by Paul Johnson (left) and Madelyn Dragone (right).
Strong birefringence was observed using cross-polarized light under microscopic analysis, with an unusual radial pattern (figure 3, left) signifying unique growth conditions compared to typical CVD diamonds available in the market today. The deep ultraviolet illumination of the DiamondView (figure 3, right) confirmed these unusual growth features with a lack of post-growth fluorescence colors such as green produced by the H3 center.
The solid laboratory-grown diamond ring was studied by GIA and determined to have VVS2 clarity based on dark non-diamond carbon pinpoint inclusions (growth remnants typical of CVD-grown diamonds) with Good polish (polishing on the interior surface of the ring precluded Very Good). Although the ring was a near-perfect circle (figure 2), symmetry was considered not applicable. The diamond had an E color specification based on GIA’s color grading scale. The ring was laser inscribed “Laboratory-Grown” on a side facet.
The quality and size of this solid diamond ring (see the video below) provide a great example of the advancing technology in laboratory-grown diamonds and changing trends in the jewelry industry. This is the first time a GIA laboratory has examined a colorless diamond ring fashioned entirely from a laboratory-grown diamond.

	Solid CVD-Grown Diamond Ring @topic:4


Publish Year: 2023 Title: CVD-Grown Diamond with Few Diagnostic Features Abstract: Figure 1. The PL spectra for a 1.40 ct CVD-grown diamond are shown in red. Left: The 514 nm PL spectrum reveals relatively weak NV centers and no detectable silicon. For comparison, the 514 nm PL spectrum for a more commonly observed as-grown CVD (purple) shows much stronger NV centers and detectable silicon. The Raman lines (not shown) are scaled as equal. Spectra are offset vertically for clarity. Right: Many locations on the CVD-grown diamond were analyzed with 457 and 633 nm excitation to verify whether the 468 nm center or the SiV– center could be detected; this very weak peak of the 468 nm center was only detected at the culet.
Diamonds grown by chemical vapor deposition (CVD) have evolved rapidly in the last two decades. However, the vast majority submitted to GIA for reports still show several diagnostic features such as the silicon vacancy or SiV– defect (a doublet at 736.6 and 736.9 nm) and/or the 468 nm peak when analyzed by photoluminescence (PL) spectroscopy. Additionally, most CVD diamonds have distinctive fluorescence images when analyzed by deep UV with the DiamondView instrument.

Figure 2. Left: The deep-UV (<230 nm) fluorescence image showed blue coloration (due to the presence of dislocation bundles) that appeared nominally similar to DiamondView images of natural type IIa diamonds. Right: When the fluorescence was filtered by an orange long-pass filter that blocked wavelengths below 550 nm, the NV-related fluorescence and the striations indicative of CVD growth became apparent. Image by Sally Eaton-Magaña (right).
Therefore, it was interesting to analyze a 1.40 ct E-color, VVS2 type IIa diamond submitted for a laboratory-grown diamond report. Initial PL data collection did not show either the SiV– center or the 468 nm peak. The features observed were a 3H peak at 503.5 nm using 455 nm excitation and relatively weak nitrogen vacancy (NV) centers at 575 (NV0) and 637 (NV–) nm using 514 nm excitation (figure 1, left). The stone showed weak anomalous birefringence indicating strain; while this observation is helpful in confirming whether a diamond is grown by high-temperature, high-pressure (HPHT) methods, such birefringence cannot distinguish between natural and CVD origins. The deep-UV fluorescence image showed only deep blue coloration, which appeared generally comparable with the vast majority of natural type IIa diamonds (figure 2, left). Therefore, many of the standard markers of CVD origin were not present even when examined using advanced methods. Careful analysis of the fluorescence image revealed some distinct differences from the majority of natural diamonds, namely the patchiness of the fluorescence with some inert regions.
Many models of the DiamondView instrument include a series of filters that permit fluorescence imaging in which portions of the visible spectrum are blocked out. Using these filters, the blue portion of the visible spectrum was blocked in order to observe weaker underlying fluorescence features. With the orange long-pass filter blocking wavelengths less than 550 nm, NV-related fluorescence clearly showed the striations indicative of CVD growth (figure 2, right). Also, several locations of the diamond were analyzed with PL spectroscopy to determine if either the 468 nm center or the SiV– could be detected. Only at the culet was a small 468 nm feature observed (figure 1, right).
The author concluded that this was a CVD-grown diamond with no evidence of post-growth treatment. This example is a noteworthy indicator that as CVD growth methods improve, telltale defects are being minimized or eliminated entirely. Careful examination of all data, both spectroscopic and fluorescence imaging, is needed to provide accurate origins for diamond. @topic:4


Publish Year: 2022 Title: Natural Near-Colorless Type IIb Diamond Abstract: Figure 1. FTIR spectrum of the sample showing a band (2802 cm–1) characteristic of type IIb diamond.
While colorless to near-colorless HPHT laboratory-grown diamonds usually contain detectable boron impurities (classified as type IIb; see S. Eaton-Magaña et al., “Observations on HPHT-grown synthetic diamonds: A review,” Fall 2017 G&G, pp. 262–284), it is uncommon to encounter a boron-bearing diamond of natural origin due to its rarity (0.02% of natural gem diamonds; E.M. Smith et al., “Blue boron-bearing diamonds from Earth’s lower mantle,” Nature, Vol. 560, No. 7716, 2018, pp. 84–87). The boron concentrations in natural diamonds are generally low (typically <1 ppm), but boron is such an efficient coloring agent that it imparts a blue color to most type IIb diamonds. However, exceptions still exist. For example, when boron absorption is accompanied by absorptions from plastic deformation, the combined effects may give rise to other colors (e.g., yellowish green; Spring 2012 Lab Notes, pp. 47–48; see also Summer 2009 Lab Notes, p. 136). Occasionally, some type IIb diamonds are near-colorless because their boron concentrations are too low to cause a blue color (e.g., E. Fritsch and K. Scarratt, “Natural-color nonconductive gray-to-blue diamonds,” Spring 1992 G&G, pp. 35–42), but they are far from common. Therefore, any near-colorless type IIb diamond submitted to a gem laboratory should be given particular attention to determine its possible lab-grown origin.

Figure 2. DiamondView imaging of the 0.24 ct diamond revealed blue fluorescence (left) and moderate blue-green phosphorescence (right). Subtle dislocation networks on the table (red arrow) that resulted from plastic deformation, typically observed in type IIa and IIb diamond, are consistent with a sublithospheric origin. Images by Wenqing Huang.
Recently, we had the opportunity to examine such an example. This 0.24 ct round brilliant cut had an I color grade due to its grayish component, usually seen in natural type IIb diamond. Fourier-transform infrared (FTIR) absorption spectroscopy detected a weak band at 2802 cm–1 (figure 1), characteristic of uncompensated boron, and identified the sample as type IIb. The diamond was inert to both long- and short-wave ultraviolet radiation. When observed with the DiamondView, it exhibited blue fluorescence and moderate blue-green phosphorescence (figure 2). The dislocation networks observed on the table (figure 2, left), typically seen in some natural type IIa and IIb diamonds but not previously described for lab-grown diamonds, suggest a natural origin. Further evidence of natural origin came from photoluminescence (PL) spectroscopy and inclusion analysis.

Figure 3. Photoluminescence spectra from the type IIb diamond under 473 nm and 532 nm laser excitations. Nitrogen-related defects such as H4 (top) and NV0 (bottom) were observed, along with GR1 (bottom).
Multiple laser excitations (473, 532, and 633 nm) were used to characterize its photoluminescence features at liquid nitrogen temperatures. The PL spectrum measured with a 473 nm excitation revealed the presence of nitrogen-related defect H4 (496.0 nm) (figure 3, top). PL spectroscopy using a 532 nm laser (figure 3, bottom) revealed the occurrence of GR1, NV0, and a sharp peak at 648.2 nm that is probably related to interstitial boron, all of which have been documented previously in type IIb diamonds (S. Eaton-Magaña et al., “Natural-color blue, gray, and violet diamonds: Allure of the deep,” Summer 2018 G&G, pp. 112–131). Nickel defect-related peaks (883/884 nm), a common feature in HPHT laboratory-grown diamonds of various colors, were not detected with any of these excitations.

Figure 4. Inclusions (outlined in red circles) observed in the type IIb diamond tended to show a satellite-like appearance. Fields of view are 2.5 mm (left) and 2 mm (right), respectively. Photomicrographs by Wenqing Huang.

Figure 5. Raman spectra of mineral inclusions in the type IIb diamond. Left: Baseline-corrected Raman spectra of a mineral inclusion (blue line) match the CaTiO3 perovskite reference spectrum (light gray line) from Nestola et al. (2018). The included mineral could be perovskite or CaSiO3 perovskite, since their Raman spectra are almost indistinguishable. Right: Baseline-uncorrected Raman spectrum of a coesite inclusion inverted from the presumed stishovite, showing main bands at approximately 530, 272, and 195 cm–1. Reference spectrum is from RRUFF-X050094.
Magnification indicated several solid inclusions (figure 4), mostly in the crown, that resulted in its SI1 clarity grade. The inclusion scenes were consistent with those described in natural type IIb blue diamonds (Smith et al., 2018). Namely, they tended to show a tiny satellite-like appearance composed of the main inclusion and accompanying decompression cracks. Raman spectra using a 532 nm laser revealed that two of these inclusions were coesite (figure 5). This feature confirmed the diamond’s natural origin. Coesite is a relatively common inclusion in lithospheric diamonds that formed at depths of ~150–200 km. However, recent studies show that type IIb diamonds have a sublithospheric origin and are formed in the upper part of the lower mantle (Smith et al., 2018). For type IIb diamond formed at such depths, the coesite inclusion has not been considered to be in its original pristine form, but rather the back-transformation product from stishovite. Another inclusion showed bands matching roughly with perovskite (CaTiO3) (figure 5), but its precise mineralogy was difficult to determine. This is because the Raman spectra of perovskite and CaSiO3 perovskite, both of which have been described in sublithospheric diamonds, are very similar (F. Nestola et al., “CaSiO3 perovskite in diamond indicates the recycling of oceanic crust into the lower mantle,” Nature, Vol. 555, No. 7695, 2018, pp. 237–241). No matter what exact mineral this inclusion corresponds to, its occurrence implies a sublithospheric origin for the host diamond. Other mineral inclusions could not be identified, probably because of their depth within the diamond.
Due to the scarcity of natural type IIb diamonds, any near-colorless diamond that contains boron detectable by FTIR spectroscopy should be given close attention to determine its origin. The near-colorless type IIb diamond examined here, though rarely encountered, was identified as natural on the basis of its gemological and spectroscopic characteristics. @topic:4


Publish Year: 2018 Title: Diamonds Help Solve the Enigma of Earth’s Deep Water Abstract: Water is carried down into Earth at subduction zones by the process of plate tectonics. Much of the water escapes close behind the subduction zone, promoting melting of the mantle and giving rise to the volcanic chains in the Pacific Ocean basin known as the Ring of Fire, and many other volcanoes elsewhere. But can water be carried even further into the mantle? How would we even know? Why is it important, and what are the effects of such deep water storage? Diamonds can give us the answers to these questions. Recent discoveries of water-containing mineral inclusions and even free water held at high pressures in diamonds tell us that water is carried into Earth’s deep interior—perhaps as deep as 700 km.
Why Do Earth Scientists Want to Know the Water Content at Great Depths?
Water, Water Everywhere... Everyone can see how abundant water is at Earth’s surface from our oceans. But because water can fit into mineral structures at high pressure and the volume of Earth’s mantle is so large, there could be at least another ocean’s worth of water stored in the minerals of the mantle. To know precisely how much water and in what form it was stored would help scientists understand where the water for our oceans came from, how much water returns to the mantle through plate tectonics, and how the stored water affects the properties of the mantle.
Water in the deep earth is not always a free fluid phase, and many minerals instead have water incorporated in the crystal structure as hydrogen bonded to oxygen. Common mantle minerals such as majorite, bridgmanite, Mg-Al spinel, and olivine (and its high-pressure equivalents wadsleyite and ringwoodite), are “nominally anhydrous,” but experiments show that they have the capacity to carry and host water in such a form in their structures.
Once in the mantle, water has many important effects on the properties of the mantle. Water affects the temperature at which the mantle begins to melt, along with its physical properties such as viscosity and density. In turn, these properties influence the strength of the mantle rock (its resistance to being deformed). It therefore becomes important for our understanding of the mobility and melting of mantle rock in the deep Earth to know how much water is down there. Water-rich fluids—i.e., water solutions wherein a variety of elements, compounds, and gases may be dissolved—are also a very effective way to transport other elements between different parts of Earth. Specifically, subduction fluids can transfer elements from the surface to diamond-stable portions of Earth and may even be a critical ingredient for growing diamonds.
How Is Water Distributed, and How Does It Get into the Deep Earth? The mantle transition zone (410–660 km) is thought to be a major sink for water in the mantle (Smyth, 1987). The two key minerals that make up the transition zone, wadsleyite and ringwoodite, have been shown experimentally to host an abundance of water, up to about 3.3 wt.% and 2.2 wt.% H2O, respectively (Kohlstedt et al., 1996). Seismic images show that oceanic slabs—containing the water that was not released at shallower levels—are recycled into the mantle by subduction and can sit within the transition zone (van der Hilst et al., 1997). So both a delivery and storage mechanism for water exists for the mantle transition zone.
The water content in the lower mantle (below 660 km) is likely not as high as it is in the transition zone. Experiments show that the minerals in the lower mantle do not have a high water-carrying capacity (Inoue et al., 2010; Schmandt et al., 2014). When some oceanic slabs are subducted past the transition zone and into the lower mantle, it is expected that any water would be released upward into the overlying mantle. However, a lower mantle diamond from the Juína area of Brazil was found to contain brucite (Mg(OH)2) in association with ferropericlase ((Mg,Fe)O) (Palot et al., 2016). Water in the brucite structure likely originated as a H2O-bearing fluid film around the ferropericlase inclusion. This diamond preserved an inclusion that indicates that some water transport beyond the transition zone is possible.
EVIDENCE FOR MANTLE WATER FROM MINERALS FOUND IN SUPERDEEP DIAMONDS

Figure 1. Phase diagram showing the stability fields of H2O as liquid and ice at high pressures (modified from Lobban et al., 1998). Superdeep diamonds form at temperatures between 1300 and 1500°C (beyond scale of diagram) where H2O occurs as a liquid. As the diamond cools at the earth’s surface, H2O trapped within the diamond retains its original high pressure and recrystallizes as the high-pressure form of solid H2O known as Ice VII.
Water as a Solidified Fluid: Samples of High-Pressure Ice. Direct observations of water-rich fluids in superdeep diamonds (see box A) are rare and have only been reported in two studies. At atmospheric pressure, H2O occurs as a liquid, but at higher pressures (and relatively cool temperatures compared to mantle temperatures), H2O occurs as two different forms of ice, known as Ice VI and Ice VII (figure 1).

BOX A: DIAMOND IN THE EARTH’S MANTLE

Natural Diamond Formation. Natural diamonds typically form 150–200 km below the surface of the earth. Diamond formation does not occur everywhere at these depths, but only below the oldest continents that have been stable for billions of years; these areas are known as cratons. This is because these old cratons all have thick continental roots with cool temperature profiles conducive to diamond formation. Diamonds that form within these continental roots are known as lithospheric diamonds and are carried up to the surface of the earth by rare volcanic eruptions known as kimberlites. Other diamonds form much deeper in the earth, below these continental roots. So-called superdeep diamonds form at depths greater than 200 km in areas of the mantle known as the transition zone (410 to 660 km below the earth’s surface) and lower mantle (> 660 km). After formation they are transported to shallower depths in the mantle, likely through mantle convection cells, and then also brought to the surface by kimberlite eruptions.
Inclusions in Superdeep Diamonds Are Direct Samples of the Deep Earth. Diamonds often trap tiny pieces of their surrounding rocks as they grow. These trapped inclusions are the only direct samples we have to study the composition of the deep earth. In the absence of mineral inclusions in diamond, the way to study the earth’s composition at depth is through experimental work: subjecting minerals to high pressures in the lab to see what their properties are. This experimental work has given us a good understanding of the mineral phase transitions in the deep earth, but inclusion-bearing diamond remains an unparalleled tool to uncover the earth’s properties at depth.

Ice VI was found in fibrous diamonds from the Democratic Republic of the Congo with a remnant pressure of 1.9 GPa (Kagi et al., 2000), where 1 GPa is 1 gigapascal or 10,000 times atmospheric pressure. Ice VII was found in diamonds from Orapa (Botswana), Shandong (China), and Namaqualand (South Africa) at pressures ranging from 7 GPa to 28 GPa, which is equivalent to 220 to 880 km (Tschauner et al., 2018). Amazingly, once these water-rich fluids are trapped as inclusions in diamond, they retain some high pressure even after eruption to the earth’s surface. As the diamond cools down to ambient conditions (25°C, 100 kPa), the trapped H2O recrystallizes as Ice VI or Ice VII (figure 1).
Hydrous fluids have previously been found trapped as thin films around shallower lithospheric diamonds (again, see box A; Nimis et al., 2016). But the presence of Ice VII in superdeep diamonds confirms the presence of a free fluid phase at pressures corresponding to the transition zone and lower mantle. As discussed with the finding of hydrous ringwoodite (below), these H2O-rich fluids could represent the fluid-rich diamond-forming environment, or they could be indicative of the ambient water content of the deep Earth. A likely scenario is that H2O-rich fluids are introduced into the deep Earth through subduction, consistent with the compositions of many superdeep diamonds that indicate an affinity with subducted oceanic slabs. This suggests that these fluid-rich regions of the transition zone occur locally around subducted slabs. Only further work on other superdeep inclusion-bearing diamonds from worldwide localities will show if this is the case, or how widespread such water contents are. But the highly diverse nature of the host diamonds that have been studied already suggests that these ices may be much more common than thought—we just need to look more carefully.
Water Isn’t Always a Free Fluid Phase: Examples of Mineral-Hosted Water. Ringwoodite is a high-pressure form of olivine (Mg2SiO4) that occurs in the lower half of the mantle transition zone, where it comprises around 60% of the total mineralogy. We know this from experimental work that simulates the high-pressure conditions deep within Earth. Until 2014, ringwoodite had only been found in highly shocked meteorites. This is because at surface pressures, ringwoodite—even when confined to its diamond host—is notoriously unstable and reverts to olivine at lower pressure.
Unchanged ringwoodite from deep in Earth was found for the first time as a 30 µm inclusion trapped within a diamond from Juína, Brazil (figure 2; see also Pearson et al., 2014). Even more remarkable was that this tiny ringwoodite grain was able to provide the first direct measurement of the water content of the most common mineral in the mantle transition zone. Water content was measured using nondestructive infrared spectroscopy (IR) while the inclusion was still trapped at high remnant pressure within the diamond. When the scientists attempted to remove the inclusion from the diamond for additional measurements, it self-destructed by exploding!

Figure 2. Ringwoodite is the high-pressure form of the mineral olivine (Mg2SiO4) that occurs between 520 and 660 km below the surface of the earth in the transition zone. The first terrestrial observation of this mineral was in a diamond from Juína, Brazil (top left). Water content in this 30 µm inclusion (bottom left) is around 1.4 wt.%, indicating that the global transition zone could contain at least 2.5 times the amount of water as Earth’s oceans. The majority of diamonds come from the cratonic lithosphere (indicated here as yellow diamonds). Superdeep diamonds (indicated here as white and blue diamonds) are rarer and originate from greater depths, often from the transition zone, which extends between 410 and 660 km.
By comparing the intensity of the water peaks in the IR spectrum with those from synthetic ringwoodite with known amounts of water, the natural ringwoodite inclusion was estimated to contain around 1.4 wt.% H2O. This value could represent either a locally water-enriched portion of the mantle transition zone, perhaps associated with the fluids that formed the diamonds, or the water content of the mantle transition zone as a whole. It is interesting to note that if this water content is applied to the whole mantle transition zone, the total water content would be approximately 2.5 times the volume of water in Earth’s oceans (Nestola and Smyth, 2015).
The Tip of the Iceberg: Much Further Work Is Needed. Wadsleyite, another potential water carrier, has not yet been observed as an inclusion in diamond. This is the high-pressure phase of olivine that is found between 410 and 520 km, just slightly shallower than ringwoodite (figure 2). Finding wadsleyite, along with more occurrences of ringwoodite, and analyzing their water contents will give a better understanding of the mantle transition zone’s average water-carrying capacity. Expectations are that wadsleyite will carry at least as much water as ringwoodite. Will water in these minerals turn out to be ubiquitous? Is the earth even wetter than we thought?
Further evidence for water in mineral inclusions in many more superdeep diamonds must be sought. An easy way to start is through nondestructive infrared spectroscopy of diamonds and their inclusions, specifically looking for water and ice peaks (see Kagi et al., 2000 for example spectra). Even some lithospheric diamonds are thought to form from water-rich fluids (Stachel and Luth, 2015; Smit et al., 2016), yet observation of water in these diamonds is incredibly rare (Nimis et al., 2016). Could it be that these high-pressure ices are much more common than we thought? Could the discovery of Ice VII in Earth’s diamonds revolutionize our thinking about ice storage at high pressure in other planets of our size range, such as Mars or Venus? In any case, these secrets will be revealed by more work on diamonds. @topic:8


Publish Year: - Title: Solid Laboratory-Grown Single-Crystal Diamond Ring Abstract: Figure 1. The 4.04 ct ring fashioned from a single-crystal CVD diamond. Photo by Towfiq Ahmed.
Carved single-crystal diamond rings are rare, with few examples to reference (see Spring 2020 Lab Notes, pp. 132–133). But with advancing technology in the laboratory-grown diamond industry, the creation of solid faceted diamond rings is now a reality. Recently submitted to the New York laboratory was a 4.04 ct single-crystal laboratory-grown diamond ring (figure 1). The 3.03 mm thick band had an inner diameter of 16.35–16.40 mm and an outer diameter of 20.32–20.40 mm. The ring was produced by Dutch Diamond Technologies in collaboration with the Belgian jewelry store Heursel, established in 1745.

Figure 2. OpenCV software was used to draw perfect circles from the center of the ring, marked by a green dot. Photo by Towfiq Ahmed.
This laboratory-grown diamond ring was cut from an 8.54 ct plate grown by chemical vapor deposition (CVD). Laser cutting produced a near-perfect circular ring, as demonstrated using digital imaging analysis to measure its inner and outer circumferences (figure 2).
Manufacture of a solid single-crystal diamond ring is a very complex and challenging process. Once material is removed from the crystal, very fine fractures and imbalanced strain can have severe consequences and the ring can shatter. Processing can take more than six months. Creating the single-crystal laboratory-grown ring involved about 1131 hours of processing (including pre-grinding) in the Dutch town of Cuijk, followed by 751 hours of polishing in Belgium.
Spectroscopic analysis revealed it is a type IIa diamond (no detectable nitrogen), and no hydrogen-related peaks were detected at 3107 or 3123 cm–1. Photoluminescence spectroscopy revealed very interesting vacancy-related defects indicative of complex growth methods. A very strong emission from the silicon-vacancy (SiV–) defect was observed with 633 nm laser excitation; this is a very common feature used to identify CVD-grown diamond. The conclusion was that this ring had not undergone post-growth treatment; nevertheless, it was notable that the ring showed relatively low nitrogen-related defects such as NV centers and H3 along with no detectable 468 nm peak or the 596/597 nm doublet. P. Martineau et al. (“Identification of synthetic diamond grown using chemical vapor deposition (CVD),” Spring 2004 G&G, pp. 2–25) observed this doublet with a 514 nm laser. Also of note, there were no H3 or 468 nm centers observed with 457 nm laser excitation.

Figure 3. Strong birefringence observed under cross-polarized light (left) and blue fluorescence observed in the DiamondView (right). Images by Paul Johnson (left) and Madelyn Dragone (right).
Strong birefringence was observed using cross-polarized light under microscopic analysis, with an unusual radial pattern (figure 3, left) signifying unique growth conditions compared to typical CVD diamonds available in the market today. The deep ultraviolet illumination of DiamondView imaging (figure 3, right) confirmed these unusual growth features with a lack of post-growth fluorescence colors such as green produced by the H3 center.
The solid laboratory-grown diamond ring was studied by GIA and specified with a VVS2 clarity based on dark non-diamond carbon pinpoint inclusions (growth remnants typical of CVD-grown diamonds) with good polish (polishing on the interior surface of the ring precluded very good). Although the ring is a near-perfect circle (figure 2), symmetry was considered not applicable. The diamond has a high color based on GIA’s color grading scale. The ring was laser inscribed “Laboratory-Grown” on a side facet.
The quality and size of this solid diamond ring (see the video clip below) are a great example of the advancing technology in laboratory-grown diamonds and changing trends in the jewelry industry. This is the first time a GIA laboratory has examined a colorless diamond ring fashioned entirely from a laboratory-grown diamond.

	Solid CVD-Grown Diamond Ring @topic:4


Publish Year: 2013 Title: Undisclosed Samples of Large CVD Synthetic Diamond Abstract: Figure 1. Six large CVD synthetic diamonds (1.001–1.119 ct) were submitted for grading undisclosed. Photo by H. Kitawaki.

              In mid-2012, one of the international diamond grading laboratories in Antwerp reported undisclosed CVD synthetic diamonds, causing a stir in the diamond industry (C. Even-Zohar, “Synthetics specifically ‘made to defraud,’” Diamond Intelligence Briefs, Vol. 27, No. 709, 2012, pp. 7281–7290). Since then, reports of undisclosed CVD synthetics have also emerged from gem testing laboratories in India and China (Z. Song et al., “The identification features of undisclosed loose and mounted CVD synthetic diamonds which have appeared recently in the NGTC laboratory,” Journal of Gemmology, Vol. 33, No. 1–4, 2012, pp. 45–48). While those samples were mostly between 0.3 and 0.5 ct, the largest colorless CVD synthetic reported by a gem laboratory so far was a 1.05 ct pear shape submitted to GIA (Summer 2010 G&G Lab Notes, pp. 143–144).

In December 2012, six CVD synthetics over one carat (figure 1) were submitted to the Tokyo branch of the Central Gem Laboratory for diamond grading. These were among the largest undisclosed samples of CVD synthetic diamond ever submitted to a gem laboratory. The six round brilliants ranged from 1.001 to 1.119 ct. All had a color grade of Light yellowish gray, and their strong grayish hue made color estimation using “Cape” series master stones difficult. Four of the samples had a clarity grade of VS1, while the other two were VS2. Four samples had cut grades of Excellent, and two were Very Good.

Each sample contained a few pinpoint inclusions, which kept the clarity grades below VVS. The dark, irregularly shaped inclusions were presumably non-diamond carbon. Some samples showed dark graphitization on the girdle. A similar feature is seen in HPHT-treated diamond, which strongly suggests that these samples underwent post-growth treatment. The characteristic streak pattern of anomalous double refraction due to strain (low-order black and white interference colors) was observed in every sample. The streaks run parallel with the growth direction of the crystal, which is perpendicular to the seed face. The patterns were elongated along the crystal’s growth direction and presumably caused by dislocation during growth (figure 2). The samples were inert to long-wave UV radiation, while some of them displayed weak greenish yellow luminescence to short-wave UV.

	Figure 2. Anomalous double refraction due to stress was observed under cross-polarized filters. Contrasting black and white low-order interference colors produced the streak pattern. Photo by H. Kitawaki.
After FTIR analysis, the samples were classified as type II, which do not show any distinct absorption in the nitrogen area (1500–1000 cm–1) in diamond. Despite their yellow tint, the 1344 cm–1 absorption attributed to single substitutional nitrogen was not observed. Absorptions also originate in hydrogen at 3123 cm–1, which has been reported as a characteristic of CVD-grown diamond (W. Wang et al., “Gem-quality synthetic diamonds grown by the chemical vapor deposition method,” Summer 2012 G&G, pp. 268–283), and at 3107 cm–1, which is often seen in natural diamonds, were not recognized as clear peaks.

Photoluminescence analysis at liquid-nitrogen temperatures with various excitation wavelengths revealed peaks at 637 nm (NV–), 575 nm (NV0), 503.2 nm (H3), and 737 nm (SiV–; 736.4/736.8 doublet). With 488 nm laser excitation, five of the six samples displayed a 528 nm peak of unknown origin. With 325 nm excitation, 462 and 499 nm peaks with unknown origins were detected. These two peaks are not observed in natural diamonds. Two of the samples showed a very weak peak at 415.2 nm (N3).

When tested with the DiamondView, the samples showed blue phosphorescence and greenish blue-white luminescence. This luminescence is attributed to boron doping, an enhancement that makes the stone colorless (D.S. Misra, “Method for growing white color diamonds by using diborane and nitrogen in combination in a microwave plasma chemical vapor deposition system,” International Patent No. 2012044251).

The samples also showed the layered structure image characteristic of CVD synthetic diamond (figure 3). These UV luminescence figures, unique to CVD synthetics, are more apparent from the pavilion than from the table. Some of them displayed straight growth lines or linear structures such as slip lines, and careful observation of the entire stone (especially from the pavilion) is imperative.

	Figure 3. DiamondView fluorescence images showed a layered structure characteristic of CVD synthetic diamond. Blue phosphorescence, attributed to boron, was also observed. Photo by M. Hisanaga. @topic:4


Publish Year: 2013 Title: Three CVD Synthetic Diamonds Submitted to Mumbai Laboratory Abstract: CVD-grown synthetic diamonds continue to become more abundant in the gem market, as evidenced by several reports from major diamond-grading laboratories during the past year (e.g., C. Even-Zohar, “Synthetics specifically ‘made to defraud,’” Diamond Intelligence Briefs, Vol. 27, No. 709, 2012, pp. 7281–7283). In December 2012, three CVD synthetic diamonds were submitted to GIA’s Mumbai laboratory. In keeping with the evolving technology of the CVD process, the gemological and spectroscopic characteristics of these type IIa synthetic diamonds suggested that they experienced different growth and/or treatment histories.

One sample was a 0.93 ct very light brown (O to P range) rectangular step cut with a VVS2 clarity grade due to the presence of pinpoint inclusions and graining. Viewed under crossedpolarizers it showed heavy strain, with high-order birefringence colors. The photoluminescence (PL) spectra acquired at liquid-nitrogen temperatures using various laser excitations were dominated by the emission of [N-V]0 and [N-V]– centers (with zerophonon lines at 575 and 637 nm, respectively). These ZPLs are widened by high levels of strain and have been previously studied in CVD synthetic diamonds (W. Wang et al., “CVD synthetic diamonds from Gemesis Corp.,” Summer 2012 G&G, pp. 80–97). The [N-V]0/– peaks for this sample had full-widths at half-maximum (FWHM) of 0.43 nm and 0.35 nm, respectively. These are relatively broad compared to colorless diamonds, but consistent with the high strain observed under crossed polarizers. The 596.5/597.2 nm doublet commonly observed in “as-grown” CVD synthetic diamonds was weak, as was the 736.5/736.9 nm doublet attributed to [Si-V]–. Notably, the [Si-V]– emission was too weak to detect with the 514.5 nm laser excitation. Infrared laser excitation at 830 nm resulted in many emission peaks in the 850–880 nm region, dominated by a sharp peak at 878.5 nm whose origin has not been conclusively identified. The DiamondView fluorescence was primarily red due to the strong [N-V] centers. Although CVD-characteristic violet-blue dislocation patterns were observed, growth striations could not be discerned (figure 1A). The sample did not phosphoresce. The PL features observed, the [N-V]0/– widths, and the DiamondView behavior were similar to those reported for near-colorless CVD synthetics produced by Apollo, Inc. (e.g., W. Wang et al., “Latest-generation CVD grown synthetic diamonds from Apollo Diamond Inc.,” Winter 2007 G&G, pp. 294–312).

Figure 1. DiamondView fluorescence images show distinct colors and patterns that helped identify these as CVD synthetic diamonds. Red fluorescence with purple mottling appears in the putative “as-grown” O-P color rectangular step cut (A). The greenish blue striations in the 0.52 ct sample are more typical patterns (B). The 0.57 ct CVD synthetic demonstrates a unique combination of fluorescence features—dominant [N-V] center–related fluorescence, with minor areas showing some violet-blue dislocations and greenish blue striations (C–D). [Image A by S. Magana, images B–D by U. D’Haenens-Johansson]
The other two samples were round brilliants weighing 0.52 and 0.57 ct. Both received G color and VS1 clarity grades. The clarity grades were affected by pinpoint inclusions and small fractures. Both round brilliants were weakly strained, revealing loworder (gray and brown) interference colors. They shared several PL spectroscopic traits, including emissions from [N-V]0/–, [Si-V]–, H3 (503.2 nm), and weak N3 (415.2 nm) centers. The 596.5/597.2 nm doublet was not observed in either specimen. The absence of this feature, combined with the presence of multi-nitrogen defects such as H3 and N3, suggests that they had undergone post-growth high-temperature annealing to remove the asgrown brown coloration (again, see W. Wang et al., 2012). The FWHMs for the [N-V]0 and [N-V]– centers were 0.21 nm and 0.16 nm, respectively, for the 0.52 ct round, and 0.23 nm and 0.22 nm for the 0.57 ct sample. These were comparable to the narrowest widths reported for natural diamonds and newer-generation HPHT-treated CVD synthetics produced by Gemesis Corp., and consistent with the low levels of strain detected.

The round brilliants exhibited distinct behavior when examined using the DiamondView instrument (see figure 1, B–D). The 0.52 ct sample showed greenish blue fluorescence and clear growth striations, as well as strong green-blue phosphorescence. These observations were akin to those for HPHT-treated CVD synthetic diamonds produced by Gemesis (again, see W. Wang et al., 2012). Although green-blue phosphorescence was also observed for the 0.57 ct sample, its DiamondView fluorescence images were primarily purplish pink, with violet-blue dislocation bundles and a patch of greenish blue fluorescence. This fluorescence combination in a CVD synthetic diamond had never been observed at a GIA laboratory. The purplish pink fluorescence color was attributed to [N-V] centers. Comparison of the Raman normalized PL intensities of the peaks revealed that the [N-V]0 and [N-V]– peaks were approximately 57% and 68% more intense in the 0.57 ct round than in the 0.52 ct sample. This may explain the difference in the DiamondView fluorescence responses of these synthetic diamonds. It is possible that the 0.57 ct round was HPHT annealed at a lower temperature.

The gemological and spectroscopic observations for these three samples emphasize the variations that might be possible through different growth procedures and subsequent treatment for near-colorless to lightl brown CVD synthetic diamonds. Nevertheless, the specimens could be readily identified as synthetic by careful analysis of data from a combination of laboratory techniques. @topic:4


Publish Year: 2013 Title: Large HPHT-Treated Fancy Pink Diamond Abstract: Figure 1. This 20.32 ct pear-shaped diamond was color graded as Fancy pink. Advanced testing suggested that its strong pink color was enhanced by HPHT treatment. Photo by Jian Xin (Jae) Liao.

              These days, high-pressure, high-temperature (HPHT) treatment is very commonly applied to change diamond color. Most of the HPHT-treated pink diamonds submitted to GIA range from 1 to 2 ct, and sizes over 10 ct are extremely rare. We previously reported on a 21.73 ct HPHT-annealed Light pink diamond (see Fall 2011 Lab Notes, p. 227). We have encountered another large HPHT-treated diamond that showed stronger pink coloration.

The 20.32 ct pear-shaped brilliant submitted to the New York laboratory (figure 1) was color graded as Fancy pink. We applied FTIR, UV-visible, and PL spectroscopy to examine the color origin for this diamond. The mid-infrared spectrum confirmed it was a type IIa diamond. The UV-visible spectrum showed a broad band at approximately 550 nm, a typical cause of pink coloration in diamond. But the PL spectra suggested that the pink color was improved by HPHT treatment. Most HPHT-treated pink diamonds have a secondary color component in addition to “pure” pink, either brownish or purplish. Interestingly, this sample had no secondary color component. Such HPHT-treated pure pink is extremely rare. Some HPHT-treated diamonds may contain graphitized inclusions and/or pitted surfaces on the girdle, but this one was microscopically “clean,” both internally and on the surface. It also showed the typical tatami strain of a type II diamond when viewed in cross-polarized light, along with the high interference colors often associated with HPHT treatment (figure 2).

	Figure 2. The typical tatami strain of type II diamond was observed by viewing the sample under crossed polarizers. It also showed high interference colors, which are often observed in HPHT-treated diamonds. Magnified 30×. Photo by Kyaw Soe Moe.

This sample demonstrated the improvement of HPHT treatment techniques in achieving more intense pink coloration in large diamonds. This was one of the largest HPHT-treated pink diamonds tested in GIA’s New York laboratory. It is very difficult to detect such treated pink color using traditional gemological instrumentation, especially with stones that are free of inclusions, and advanced gemological testing is critical for this purpose. @topic:4


Publish Year: 2013 Title: Very Large CVD-Grown Synthetic Diamond Abstract: Figure 1. This 2.16 ct marquise (13.42 × 6.73 × 3.94 mm) is the largest CVD synthetic diamond tested by GIA. It had J/K color, with a brownish tint.

              In the last decade, we have witnessed rapid improvement in the quality and size of lab-grown CVD synthetic diamonds. The New York laboratory recently tested a 2.16 ct CVD synthetic from Scio Diamond Technology Corp. (figure 1), the largest specimen GIA has seen so far.
This marquise, which measured 13.42 × 6.73 × 3.94 mm, was more than twice the size of a 1.05 ct pear shape examined in 2010, previously the largest CVD synthetic tested by GIA (see Summer 2010 G&G Lab Notes, pp. 143–144). It had J/K color with a brownish tint, and microscopic observation revealed small fractures, pinpoints, and non-diamond-carbon black inclusions, resulting in an SI2 clarity grade.

The mid-infrared absorption spectrum revealed that the diamond could be classified as type IIa. It was very pure in the infrared region, with no nitrogen  or hydrogen-related absorption features. Photoluminescence analysis at liquid-nitrogen temperature with varying laser excitations displayed typical CVD features: very strong emissions from N-V centers, moderate emission lines at 736.6/736.9 nm from the [Si-V]– center, and the CVD-specific 596/597 nm pair (figure 20). Also detected was weak emission from the H3 defect with a zero-phonon line at 503.1 nm, making for an interesting combination of optical centers. Under the short-wave UV radiation of the DiamondView, the table and crown facets showed pure blue fluorescence while the pavilion displayed banded orange fluorescence with irregular blue fluorescence regions. Very strong internal stress with irregular patterns was confirmed under the microscope using cross-polarized light.

Testing of this large, gem-quality CVD synthetic underscored the rapid improvement of lab-grown diamond technology. It is foreseeable that more of these products will continue to reach the jewelry industry. @topic:4


Publish Year: 2013 Title: Diamond with Extremely Strong 578.9 nm Emission Center Abstract: Figure 1. This 4.72 ct Light blue type IIb diamond displayed some of the strongest dislocations ever observed in natural diamonds by GIA. This resulted in a hazy impression and a lower transparency than other type IIb diamonds. Photo by Jian Xin (Jae) Liao.

              Photoluminescence analysis at liquid-nitrogen temperatures and varying laser excitations has become increasingly important in diamond color origin testing. The 578.9 nm emission normally occurs with many other emission lines, and it is usually weak in natural type IIa and IIb diamonds. Meanwhile, the physical model of this optical center is unclear. The New York laboratory tested a very rare diamond that showed extremely strong 578.9 nm emission.

This 4.72 ct rectangular diamond (9.75 × 8.90 × 5.92 mm) had a color grade of Light blue and an even color distribution (figure 1). Infrared absorption spectroscopy analysis identified it as a type IIb diamond with a boron concentration of about 16 ppb. This stone showed very strong dislocations, resulting in a hazy impression and a lower degree of transparency than most type IIb diamonds. Microscopic observation revealed very strong linear graining and related high interference colors. The intensity of the dislocations was among the strongest ever observed in natural diamonds at a GIA laboratory.

The outstanding feature of this diamond was the extremely strong emission at 578.9 nm, with possible side bands at 586 and 593 nm (figure 2). No other emission line was detected in the visible light region, which is very unusual for a natural type IIa or IIb diamond. This feature was confirmed with 457 and 488 nm laser excitations. The exclusive occurrence of the 578.9 nm emission and the very strong lattice dislocations suggested that this emission was a dislocation-related optical center.

	Figure 2. The diamond showed extremely strong emission at 578.9 nm and its possible side bands at 586 and 593 nm. The exclusive occurrence of the 578.9 nm emission and the very strong lattice dislocations in this diamond suggested that the emission was a dislocation-related optical center. @topic:4


Publish Year: 2013 Title: CVD-Grown Synthetic Diamond with Aggregated Nitrogen Impurities Abstract: Figure 1. Unusual 0.94 ct yellow-brown CVD synthetic diamond. Photo by Robison McMurtry.

              Synthetic diamonds grown by the chemical vapor deposition (CVD) method have become a key topic in the jewelry industry over the past few years. These products, which can be grown at low pressures and moderately high temperatures (approximately 800–900°C), are seeing more widespread use in jewelry. CVD synthetics are almost always brown or colorless type IIa specimens with little to no FTIR-measurable nitrogen or boron impurities. A few of these synthetics have been doped with nitrogen or boron to produce rare type Ib or IIb colored samples.

Recently, an unusual 0.94 ct Fancy yellow-brown emerald cut (figure 1) was submitted to GIA for a synthetic diamond grading report. It contained a cloud of black needle-like inclusions occurring along a plane (figure 2) and showed weak green transmission with fiber-optic illumination. Under cross-polarized light, the synthetic diamond displayed a black and white mottled strain pattern, somewhat similar in appearance to the crosshatched “tatami” pattern usually seen in natural type IIa diamonds (figure 15, right). FTIR spectroscopy revealed that it was type IaA, with approximately 10 ppm of aggregated nitrogen atom pairs in the lattice (figure 16). DiamondView imaging showed red fluorescence and planar growth patterns that are common in CVD synthetic diamonds (figure 17). Photoluminescence spectroscopy detected silicon-vacancy defects introduced during the CVD growth process (not shown), and further examination of the FTIR spectrum revealed a very weak peak at 3123 cm–1 (again, see figure 3), confirming this was an as-grown CVD synthetic diamond (P.M. Martineau et al., “Identification of synthetic diamond grown using chemical vapor deposition [CVD],” Spring 2004 G&G, pp. 2–25).

	Figure 2. A cloud of needle-like inclusions was observed in the synthetic diamond (left, magnified 50×). The side view clearly showed that the cloud was confined to a plane (center; magnified 45×). With cross-polarized light, the mottled and crosshatched strain pattern was visible (right; magnified 15×). Photo by Troy Ardon.
This marked GIA’s first examination of a CVD synthetic diamond with aggregated nitrogen impurities. During HPHT treatment, nitrogen atoms typically start to aggregate as pairs at temperatures above 2000°C. Although some CVD synthetics are HPHT-treated to remove brown coloration, spectroscopic evidence indicates that this sample had not undergone such treatment. It is unclear how the nitrogen impurities came to be in their aggregated state. It is possible that a type IaA natural diamond was used as a seed crystal for multi-stage CVD growth and remains within the current gemstone, thereby producing the FTIR results. However, no clear evidence of this scenario was uncovered. More research is currently under way to understand this unusual CVD synthetic diamond with aggregated nitrogen impurities.

	Figure 3. FTIR spectroscopy revealed that the CVD synthetic diamond was type IaA with aggregated nitrogen atom pairs, the first CVD synthetic diamond GIA has seen with this configuration of nitrogen impurities. The 3123 cm–1 peak confirms this is an as-grown CVD diamond. @topic:4