Title: HPHT-Grown Colorless Diamond Displaying Unusual Phosphorescence Effects Abstract: Figure 1. Top: A series of images showing the gradual change (left to right) in the phosphorescence of the 0.71 ct HPHT-grown colorless diamond after removing it from the LWUV source (left image) in increments of 30 seconds for 150 seconds (right image). Bottom: The gradual change in phosphorescence after exposure to a SWUV source (left image) in increments of 30 seconds. The greenish blue and orange emissions decay differently, with the blue fading faster (~90 seconds, fourth image from left) than the orange (~240 seconds, right image). Images by Guy Borenstein.
Phosphorescence longer than 10 seconds in reaction to ultraviolet radiation is regularly observed in colorless to near-colorless and blue-colored diamonds grown by a high-pressure, high-temperature (HPHT) technique. The gemological laboratory of Stuller Inc. recently tested an HPHT-grown colorless (approximately E color grade with a blue-gray overtone) oval brilliant diamond weighing 0.71 ct that showed unusual fluorescence and phosphorescence reactions.
When exposed to a long-wave ultraviolet (LWUV, 365 nm) source for 60 seconds using a standard UV viewing cabinet, the stone emitted a gradually increasing strong orange fluorescence, followed by a long-lasting noticeable phosphorescence (~150 seconds, figure 1, top). The fluorescence and phosphorescence reactions demonstrated a nonuniform color distribution. Similar results were observed using other light sources, including 395 nm UV LED, 405 nm blue laser, a tungsten incandescent flashlight, and a fiber-optic halogen unit.
Given that orange phosphorescence can also be generated by low- and non-UV light sources, further analysis was performed using a series of spectral bandpass filters to identify other wavelengths that stimulate the orange phosphorescence. Testing demonstrated that medium- to strong-intensity light centered at around 430 nm produces the excitation.
Under short-wave ultraviolet (SWUV, 254 nm) radiation using a standard viewing UV cabinet and a De Beers PhosView instrument, the stone displayed a mix of strong greenish blue and medium orange zoned fluorescence and phosphorescence (figure 1, bottom). The colored phosphorescing areas decayed at different rates, with the greenish blue fading faster than the orange (~90 seconds vs. ~240 seconds, with a half-life of about 25 and 35 seconds, respectively).

Figure 2. Deep-UV imaging of the 0.71 ct colorless diamond showing a cuboctahedral-structured luminescence associated with HPHT growth. Image by Guy Borenstein.
Deep-UV (<225 nm) imaging demonstrated a strong greenish blue fluorescence with a clear cuboctahedral structure associated with HPHT growth (figure 2). After removal from the excitation source, the stone displayed a phosphorescence reaction similar to the reaction under SWUV.

Figure 3. The infrared spectrum of the 0.71 ct HPHT-grown diamond revealed it was type IIb with relatively high levels of uncompensated boron (for a colorless diamond) at 4089, 2929, 2800, and 2455 cm–1.
Infrared spectroscopy revealed a type IIb diamond with relatively high levels of electrically uncompensated boron at 4089, 2929, 2800, and 2455 cm–1 (figure 3). Photoluminescence spectroscopy with 532 nm laser excitation at liquid nitrogen temperature (77K) showed no results, except for the diamond’s first- and second-order Raman spectrum peaks, a common tendency in HPHT-grown colorless diamonds (S. Eaton-Magaña et al., “Observations on HPHT-grown synthetic diamonds: A review,” Fall 2017 G&G, pp. 262–284).
The two phosphorescence colors emitted and their relatively long duration are well-known properties of HPHT-grown diamonds (S. Eaton-Magaña and R. Lu, “Phosphorescence in type IIb diamonds,” Diamond and Related Materials, Vol. 20, No. 7, 2011, pp. 983–989; Eaton-Magaña et al., 2017), and a blue-orange luminescence combination in one gem was also previously reported (Eaton-Magaña and Lu., 2011; B. Deljanin et al., “NDT breaking the 10 carat barrier: World record faceted and gem-quality synthetic diamonds investigated,” Contributions to Gemology, Vol. 15, No. 1, 2015) but of weaker intensity. The laboratory-grown diamond’s property of bicolor, decay-varying phosphorescence has been previously reported as well (K. Watanabe et al., “Phosphorescence in high-pressure synthetic diamond,” Diamond and Related Materials, Vol. 6, No. 1, 1997, pp. 99–106; Eaton-Magaña and Lu, 2011; Ulrika F.S. D’Haenens-Johansson et al., “Large colorless HPHT-grown synthetic gem diamonds from New Diamond Technology, Russia,” Fall 2015 G&G, pp. 260–279).
Considering the HPHT growth method, the long-lasting greenish blue phosphorescence produced by exposure to SWUV and deep UV was expected. It was previously suggested to be related to nitrogen-boron donor-acceptor pair recombination (Watanabe et al., 1997). However, the orange phosphorescence demonstrated a new stimulation source. Its combination with the greenish blue phosphorescence and the identified visible-light excitation wavelength reinforces the theory that the recorded orange phosphorescence is of a different donor-acceptor pairing.
Light of 430 nm wavelength can be found in most fluorescent and all incandescent indoor light sources, as well as the desk lamps and color grading cabinets found in gemological laboratories. Therefore, considering the possibility of more diamonds with this property in the market, their phosphorescence produced from visible light makes it challenging to assign a color in the colorless to near-colorless range for these diamonds during grading. Even under standard non- or low-UV output 6500K fluorescent bulbs, the orange luminescence generated by the source becomes noticeable, adding a yellowish overtone to the blue-gray bodycolor and changing its apparent color grade to approximately F to G. Such a change may impair the diamond grader’s ability to accurately assess the stone’s bodycolor. Source: GIA @topic:4


Title: Grayish Blue CVD Diamond Colored by GR1 and SiV– Abstract: Figure 1. Left: This 1.63 ct grayish blue diamond was identified as a CVD synthetic, with its color caused by both the GR1 and SiV– centers. Photo by Xiaoyu Zhang. Right: Dark cloud-like non-diamond carbon inclusions. Photomicrograph by Meng Li; field of view 0.25 mm.
Silicon is a common impurity in chemical vapor deposition (CVD) laboratory-grown diamond. The silicon-related SiV– center, which has zero-phonon lines at 736.6 and 736.9 nm and is active in absorption and luminescence, is widely considered an identifying feature of CVD diamond. Generally, the SiV– center is detected by photoluminescence spectroscopy and is not observed using absorption spectroscopy for most CVD synthetics due to the low silicon content. The absorption spectra may reveal the presence of the SiV– center in the case of a relatively high silicon content, but rarely in amounts significant enough to affect the color. When the silicon content becomes particularly high, the absorption of SiV– is in sufficient concentration to influence the bodycolor of a diamond. It has been reported that the color of silicon-doped blue CVD diamonds produced by the PDC Company is attributed to strong absorption of the rather intense SiV– center (A. Peretti et al., “New generation of synthetic diamonds reaches the market (Part A): Identification of CVD-grown blue diamonds,” Contributions to Gemology, No. 14, 2013, pp. 3–20).

Figure 2. In the Vis-NIR region, in addition to very strong absorptions at 737 nm (SiV–) and 741 nm (GR1), weak absorptions at 830, 856, and 946 nm (SiV0) were observed.
National Gemstone Testing Center’s (NGTC) Beijing laboratory recently received a 1.63 ct grayish blue princess cut (figure 1, left) for identification. Standard testing identified it as a CVD synthetic diamond. The sample showed an even color distribution. Microscopic investigation revealed abundant non-diamond carbon inclusions in the form of both crystals and clouds, with the clouds distributed along the growth layer (figure 1, right). The visible/near-infrared (Vis-NIR) spectrum (figure 2), recorded at liquid nitrogen temperature, included a strong broad SiV– center defect at 737 nm next to an equally strong GR1 center. The diamond’s grayish blue bodycolor was attributed to both the strong GR1 center and the high intensity of the SiV– center, which produced preferential absorption in the red part of the spectrum. In addition, weak absorptions at 830, 856, and 946 nm (the SiV0 center) were observed, which were also reported in CVD synthetic diamonds with high silicon content (Peretti et al., 2013; Z. Song et al., “Silicon-doped CVD synthetic diamond with photochromic effect,” Journal of Gems and Gemmology, Vol. 18, No. 1, 2016, pp. 1–5).

Figure 3. DiamondView imaging showed green fluorescence with blue dislocations. The diamond also revealed a layered growth structure, indicating a start-stop cycling growth process typical of CVD diamond, as CVD diamond growth takes place layer by layer on the top surface of the growing crystal. Image by Xiaoyu Zhang.

Figure 4. The PL spectrum of the grayish blue CVD synthetic diamond obtained with 473 nm excitation (A) showed that the H3 center (503.2 nm) and radiation-related features included very strong 3H at 503.5 nm and weak 486.3 nm. B: 532 nm excitation revealed the NV centers and silicon-vacancy center that are typically observed in CVD-grown diamonds, along with strong GR1. C: 785 nm excitation showed the H2 center at 986 nm.
Infrared spectroscopy showed features typical for type IIa diamond (i.e., no defect-related absorptions were detected). The diamond was inert to short-wave and long-wave ultraviolet illumination. Under the ultra-short-wave UV radiation of the DiamondView, the sample fluoresced green, with minor areas showing some blue dislocations. It also showed subtle growth striations and two parallel planes fluorescing stronger than the bulk of the crystal (figure 3). The sample did not phosphoresce. Photoluminescence (PL) spectra taken with various laser excitation wavelengths and at liquid nitrogen temperature (figure 4) showed the presence of radiation-related features including very strong 3H at 503.5 nm, strong GR1 at 741 nm, and weak 486.3 nm. The PL spectra also indicated strong nitrogen-vacancy centers at 575 NV0 and 637 NV– nm and multi-nitrogen defects such as H3 and H2, combined with the absence of the unassigned 596/597 nm doublet that is normally seen in as-grown CVD synthetics, suggesting that it had undergone post-growth high-temperature annealing before irradiation.
The PL spectrum with 532 nm laser excitation also exhibited a rather large silicon doublet peak at 736.6/736.9 nm that dwarfs all other PL peaks, including the GR1 in the spectrum. The intensity ratio between the 736.6/736.9 nm PL peak and the diamond Raman peak was about 52. The PL spectrum reaffirmed that the 737 nm absorption peak of the ultraviolet/visible spectrum was the SiV– defect, and the silicon content of this diamond was so high that it produced strong absorption in the red range of visible light and affected the color of the diamond together with the GR1 center. Source: GIA @topic:4


Title: CVD Diamond Over 34 Carats Examined in GIA’s Hong Kong Laboratory Abstract: Figure 1. This 34.59 ct CVD-grown diamond (24.94 × 13.95 × 9.39 mm), produced by Ethereal Green Diamond in India, is the largest GIA has tested. Photo by Johnny (Chak Wan) Leung.
Chemical vapor deposition (CVD) growth technology has advanced significantly over the last two decades. In this study, we report on the largest CVD gem diamond GIA has encountered, recently tested in the Hong Kong laboratory. This emerald-cut diamond weighed 34.59 ct, measuring 24.94 × 13.95 × 9.39 mm (figure 1), produced by Ethereal Green Diamond in India. It had G color and VS2 clarity. Small black graphite inclusions were found. Some stood alone inside the body, while others formed clusters of clouds located between growth layers. Microscopic observation showed a weak oily or wavy graining looking through the table facet, a feature sometimes seen in CVD gem diamonds. It tends to appear more prominent in CVD diamonds with high amounts of strain and a strong birefringence pattern when viewed through crossed polarizers (figure 2).

Figure 2. A high amount of strain and a strong birefringence pattern were observed using crossed polarizers. Photomicrograph by Ka Wing Tam; field of view 15.92 mm.

Figure 3. Left: The PL spectrum with 514 nm laser excitation under liquid nitrogen temperature showed features of treated CVD diamond. Right: The PL spectrum with 457 nm laser excitation under liquid nitrogen temperature recorded a strong H3 defect and a negligible 467.6 nm center.
Infrared absorption spectroscopy revealed no absorption related to nitrogen, which is consistent with type IIa diamond. However, a weak absorption related to boron (an absorption peak at ~2800 cm–1) was detected, corresponding to around 2 ppb of boron impurity. This trace amount of boron was very likely incorporated as contamination during diamond growth. There are different opinions on whether this trace contamination should be considered in diamond classification. Photoluminescence (PL) spectroscopy was performed at liquid nitrogen temperature (–196°C) with several laser excitations (figure 3). In addition to strong emissions from NV0 and NV– centers at 575 nm and 637 nm, respectively, moderately strong doublet emissions from SiV– at 736.6 and 736.9 nm were recorded. A weak emission at 946.4 nm, possibly from the SiV0 defect, was also observed. Other important emission features included a strong emission from the H3 defect at 503.2 nm and a weak emission band with peaks at 566.0, 566.7, and 567.7 nm. Emissions at 596/597 and 467.6 nm, which are common in as-grown CVD diamonds, were reduced by high-temperature treatment. These observations and spectroscopic features confirmed that this CVD diamond was annealed under high pressure and high temperature (HPHT) to improve its color appearance. In contrast, no post-growth color treatment was applied to the 16.41 ct CVD lab-grown diamond tested a year earlier in the New York laboratory (W. Wang et al., “New record size for CVD laboratory-grown diamond,” GIA Research News, January 27, 2022).

Figure 4. DiamondView imaging revealed at least eight growth steps. Image by Ka Wing Tam.
DiamondView fluorescence imaging showed green and blue colors with a banded pattern. Typical CVD growth striations were clearly visible (figure 4). Green fluorescence was from the H3 defect, produced during HPHT annealing. This banded structure revealed at least eight growth steps to achieve sufficient depth for this large diamond. Additionally, strong blue phosphorescence with similar banding was detected in the DiamondView.

This very large CVD diamond represents a milestone in CVD growth. Mined diamonds with similar size and quality are very rare. We will continue monitoring developments in gem diamond growth technology to ensure all diamonds are properly identified in GIA laboratories. Source: GIA @topic:4


Title: Rare Mixed Type IaB-IIb Diamond with a Long-Lasting Phosphorescence Abstract: Figure 1. The 0.20 ct diamond’s FTIR spectrum. Insets show the type IaB aggregate nitrogen at 1175 and 1010 cm–1 (top inset) and IIb boron (bottom inset) at 3725 and 2803 cm–1, confirming a mixed-type stone.
Phosphorescence is an optical effect in which electromagnetic radiation absorbed by a substance is released relatively slowly in the form of light. Long-lasting UV phosphorescence of more than 10 seconds’ duration is an extremely rare property in natural diamonds, normally limited to hydrogen-rich type Ia chameleon and type IIb diamonds.
Recently, a natural round brilliant weighing 0.20 ct (E-F color, VS2-SI1 clarity) was submitted to Stuller Inc. by a client for a custom design. During our diamond screening process, using a phosphorescence imaging-based screening device, the diamond was automatically identified as having an HPHT-grown origin, conflicting with the client’s natural origin disclosure. Secondary testing, using a fluorescence spectroscopy-based screening device, identified the diamond as having a natural origin. Under magnification, only a few pinpoints were spotted.
Due to the ambiguous results, the gem was sent to Stuller’s Gem Lab for further analysis. The FTIR spectrum (figure 1) showed a mixed diamond type comprising low levels of aggregated nitrogen (IaB) and boron (IIb), indicating a natural origin. Similar results were given using fluorescence spectroscopy, which identified N3 peaks, associated with natural origin. Photoluminescence spectroscopy, using a 532 nm laser under liquid nitrogen temperature (77 K), provided results supporting the other instruments and confirming the absence of synthetic origin-related peaks.

Figure 2. The 0.20 ct diamond’s phosphorescence, as seen immediately after exposure to UV radiation (left) and after 60 seconds of elapsed time (right). Images by Guy Borenstein.
In order to identify the cause of the false positive results from the first screening device, the diamond was placed in a SWUV cabinet to analyze its phosphorescence effect. Once excited, the stone emitted a strong bluish green phosphorescence for about 120 seconds (figure 2).
The emitted color and the unusually long duration of the effect are typically associated with HPHT-grown diamonds. Consequently, these properties triggered the false positive results in the phosphorescence imaging-based screening device. In this case, the rare combination of natural diamond types, which includes a boron component, was probably the reason for the unusual phosphorescence.
This case demonstrates the complexity of diamond origin identification and the need for multiple diamond screening devices, each with a different screening technology, to cover all possibilities and ensure a 100% correct identification. Source: GIA @topic:4


Title: HPHT Synthetic Diamond Melee Without Si or Ni Defects Abstract: Figure 1. These four near-colorless round brilliant melee were identified as HPHT synthetic diamonds lacking the typical Si- and Ni-related defects. Photo by Nuttapol Kitdee.

	Near-colorless synthetic diamond melee grown using the high-pressure, high-temperature (HPHT) method have created significant concern in the industry, and various screening methods have been developed to take into account their most reliable distinguishing features. In general, the specimens described in previous Lab Notes (e.g. Summer 2015, pp. 183–184) were very small round faceted goods ranging between 0.005 and 0.01 ct.

	Recently GIA’s Bangkok laboratory received four loose near-colorless round brilliants for quality assurance service (figure 1). They weighed between 0.07 and 0.09 ct, slightly more than previously submitted melee. All were identified as type IIb HPHT-grown material using Fourier-transform infrared (FTIR) spectroscopy. Their most interesting feature was the absence of silicon- or nickel-related emission peaks when analyzed at liquid nitrogen temperature by photoluminescence (PL) spectroscopy (figure 2). The spectra typically observed in HPHT synthetic diamonds show an emission doublet related to the negatively charged silicon split-vacancy defect SiVˉ at 736.6/736.9 nm and an associated Ni-related defect at 883.0/884.7 nm.

	Figure 2. The PL spectra features observed at liquid nitrogen temperature lacked the 736.6/736.9 nm emission doublet related to the SiV– defect (left, 514 laser excitation) and the Ni-related defect doublet at 883/884 nm (right, 830 nm laser excitation).

	The growth patterns observed in the DiamondView were an identifying feature that did remain the same. The characteristic angular growth patterns and blue-green fluorescence, together with an associated green phosphorescence, still provide important evidence that aid in the separation of natural and synthetic diamonds (figure 3). Examination with a gemological microscope revealed metallic and rod-like inclusions (figure 4) that also assisted in identifying these melee as synthetic diamonds.

	Figure 3. These DiamondView fluorescence and phosphorescence images of a 0.081 ct sample show growth patterns characteristic of HPHT synthetic diamond. Image by Charuwong Khowpong.

	Figure 4. Darkfield illumination reveals rod-like inclusions in a 0.087 ct HPHT-grown melee diamond. Photomicrograph by Charuwan Khowpong and Ungkhana Atikarnsakul.

	The study of these four melee-size HPHT synthetic diamonds revealed atypical PL spectra. However, other means of identification (inclusions, growth patterns as seen via the DiamondView, and their phosphorescence reactions) still played an important role in their identification. It is interesting to note that HPHT synthetic melee diamonds being submitted to GIA for identification are getting larger, indicating the continuous improvement of synthetic technology. Source: GIA @topic:4


Title: 10 ct HPHT-Treated CVD Laboratory-Grown Diamond Abstract: Figure 1. This 10.04 ct G-color CVD-grown diamond proved to have been HPHT treated. Photo by Annie Haynes.
Recent years have seen several size milestones for faceted diamonds grown by chemical vapor deposition (CVD). In all the published reports that commented on treatment, these record-size CVD diamonds were indicated to be as-grown and with no indications of post-growth treatment (Winter 2016 Lab Notes, pp. 414–416; “IGI Hong Kong certifies largest CVD grown diamond to date,” 2020, https://www.igi.org/gemblog/igi-hong-kong-certifies-largest-cvd-grown-diamond-to-date/; Spring 2022 Lab Notes, pp. 54–56). For other recent milestone CVD diamonds reported within the trade, we could not confirm whether they were as-grown or treated. At the time of publication, the current benchmark is a 30.18 ct H-color diamond reportedly grown by Ethereal Green Diamond (Rapaport News, June 12, 2022).

Figure 2. The green and blue fluorescence colors in this DiamondView image of the 10.04 ct CVD-grown diamond confirm its post-growth treatment. Image by Taryn Linzmeyer.
Against this backdrop, a notable 10.04 ct CVD-grown diamond (figure 1) was recently submitted to the Carlsbad laboratory for a laboratory-grown diamond report. This emerald-cut stone with G color and VS2 clarity had several growth remnants, including a cloud of dark non-diamond carbon. As with all laboratory-grown diamonds, it underwent extensive testing including spectroscopy to verify its CVD origin. IR absorption spectroscopy identified it as type IIb with an uncompensated boron concentration of ~2 ppb. Spectral features such as the lack of a 468 nm peak in photoluminescence along with the coloration in the DiamondView fluorescence imaging (figure 2) confirmed it had undergone post-growth treatment (W. Wang et al., “CVD synthetic diamonds from Gemesis Corp.,” Summer 2012 G&G, pp. 80–97).
Many CVD-grown diamonds are subjected to high-pressure, high-temperature (HPHT) treatment after growth to remove a brownish appearance caused by extended defects (such as vacancy-related complexes). The brown color often correlates with a faster CVD growth rate, which the manufacturer uses knowing the color can be reduced by treatment afterward. It appears that when manufacturers create a CVD diamond of record-setting size, the growth is performed so slowly that subsequent HPHT treatment is not required for a colorless to near-colorless grade.
While some 80% of colorless to near-colorless CVD-grown diamonds have been subjected to post-growth treatment to reduce their brownish coloration (S. Eaton-Magaña et al., “Laboratory-grown diamond: A gemological laboratory perspective,” Journal of Gems & Gemmology, Vol. 23, No. 6, 2021, pp. 25–39), this treatment is not often applied to larger stones. Therefore, evidence of HPHT treatment in a CVD-grown diamond larger than 10 carats is noteworthy. These products will likely become more commonplace in the future. Source: GIA @topic:4


Title: Diamonds from Guyana, Ekanite from Sri Lanka, a New Amber Source in Vietnam, and More... Abstract: Welcome to the Summer 2022 issue of Gems & Gemology! This installment is packed with interesting new content, including five feature articles ranging from reports on new and lesser-known gem sources to a study of the emeralds once embedded in the crown of Napoleon III.
“…an overview of diamond production and mining practices in Guyana, along with findings on color…”
In our lead article, Roy Bassoo and Kenneth Befus explore diamonds and diamond mining in Guyana. Drawing on their own observations of diamonds from various alluvial deposits, coupled with government reports, datasets, and historical accounts, the authors provide an overview of diamond production and mining practices in Guyana, along with findings on color, morphology, nitrogen content, and luminescence.
Our second article investigates the uneven shapes and surface features of ekanite from Sri Lanka. Lutz Nasdala and his team analyze ekanite fragments and ekanite-containing specimens of rock discovered near Ampegama, comparing the samples to those from other Sri Lankan sources to identify the processes that led to the distinctive shape and surface features.
As part of an ongoing effort to research gemstones of historical significance, Stefanos Karampelas and coauthors present their analysis of 45 “emeralds” formerly set in the coronation crown of Napoleon III. Using nondestructive mobile spectroscopic and gemological means at Mines Paris - PSL, they verified that 41 of these 45 gems were emeralds, likely of Colombian provenance, while the remaining four were glass containing iron and/or copper.
Next, a team led by Le Ngoc Nang examines the gemological properties and commercial potential of a newly discovered amber source on Phu Quoc island in Vietnam. They conclude that based on the high quality of the amber and the wide distribution of the host rock on the island, Vietnam’s only known amber locality may have a promising future in the market.
In our final article, Dariusz Malczewski and colleagues present their study on natural radioactivity in nephrite. After examining 11 serpentinite-related nephrite samples from Poland, Russia, Canada, and New Zealand, the authors determined that there is no radiological risk to handling nephrite and that the levels of the radioactive isotopes studied are very low.
Our regular columns deliver interesting finds from around the world. Highlights from the Lab Notes, section include a very rare large bright orange benitoite, the famed De Beers Cullinan Blue diamond, and pearls embedded with RFID devices. In Micro-World, the inner beauty of gems comes alive with an impressive blue apatite inclusion in garnet, eye-visible etch channels in a natural diamond, and a rock fragment exhibiting a very realistic eye pattern. Gem News International keeps you up to date with the latest developments, including unusual chatoyancy in omphacite fei cui jade, a company with a mission to support women in the gem trade, testing of color instability in yellow sapphire, and a museum exhibit celebrating a major tourmaline discovery in Maine. Colored Stones Unearthed returns to cover inclusions in gems, explaining how they form, how they are studied, and what they mean for gemologists and geoscientists.
Finally, we invite you to join the Gems & Gemology Facebook group at www.facebook.com/groups/giagemsgemology. Since its launch in February 2020, our growing community has surpassed 25,000 members. Thank you for your continued support and interest in G&G! Source: GIA @topic:1


Title: Acicular Troughs Coincident with Green Stains on Rough Diamond Surface Abstract: Figure 1. A ~0.12 ct green-skinned diamond from Guyana. Photo by Roy Bassoo.
The author acquired an alluvial rough diamond from Guyana showing unique surficial features that do not appear to have been documented elsewhere. The specimen was a twinned crystal consisting of two intergrown octahedral crystals, ~0.12 ct in weight, with numerous flat-bottomed hexagonal etch features and trigons and a nearly pervasive green skin (figure 1). Most interesting were fine, linear, and randomly oriented features on the diamond surface that were spatially associated with the green stains (figure 2). Radiation stains are known to cause localized expansion in diamond (L. Nasdala et al., “Radio-coloration of diamond: A spectroscopic study,” Contributions to Mineralogy and Petrology, Vol. 165, 2013, pp. 843–861; S.C. Eaton-Magaña and K.S. Moe, “Temperature effects on radiation stains in natural diamonds,” Diamond and Related Materials, Vol. 64, 2016, pp. 130–142). These features also cross-cut trigons, implying that they post-date the diamond’s growth in the earth’s mantle and its surface dissolution within the kimberlite magma (figure 3). These features may be the result of localized dissolution caused by proximal acicular, radioactive, and as yet unknown minerals, leaving behind a cast impression. Green color in diamond can be produced by natural irradiation of the crystal lattice by exposure to radiation from proximal and adjacent radioactive grains (e.g., zircon, monzonite, uraninite, and K-feldspar) or salts dissolved in percolating fluids surrounding the diamond (C.M. Breeding et al., “Natural-color green diamonds: A beautiful conundrum,” Spring 2018 G&G, pp. 2–27). Gamma, alpha, or beta radiation emanating from these sources are thought to cause collections of defects and impurities within the diamond. Gamma and beta radiation have low energies and long penetration depths producing green bodycolors. Due to its high energy, alpha radiation has the shortest penetration depth and only within the first 25 μm of the diamond surface, creating green skins, stains, and spots.

Figure 2. Left: A magnified view of green radiation stains on an unpolished diamond surface in transmitted light. Right: An image of the same surface in reflected light with the radiation staining (outlined in red) and preserved acicular troughs. Photomicrographs by Roy Bassoo; field of view 0.5 mm.

Figure 3. A further magnified view of the green radiation stains on an unpolished diamond surface in transmitted light (left) and an image of the same surface in reflected light with the radiation staining outlined in red and preserved acicular troughs which cross-cut a flat-bottomed trigon (right). Photomicrographs by Roy Bassoo; field of view 0.25 mm.
Although unusual, radiation-related surface features have been previously documented (e.g., Spring 2021 G&G Micro-World, pp. 66–67). The ones seen in this diamond from Guyana appear to be unique, however. It is quite likely that these features are pervasive in placer diamonds but have not been studied in detail. Source: GIA @topic:4


Title: A Review of the Political and Economic Forces Shaping Today’s Diamond Industry Abstract: During the past 15 years, political and economic forces have converged to radically transform the structure of the diamond industry worldwide. This article examines how upheavals in the former Soviet Union and several African nations—as well as the arrival of new sources such as Australia and Canada—led to the restructuring of the rough diamond market. This in turn created new competitive pressure at the wholesale and retail levels, including the movement to establish new diamond cuts and diamonds as branded items. At the same time, technological advances have enabled the faster, more efficient manufacturing of rough diamonds, created new treatments, and fostered the introduction of economically viable gem-quality synthetics. While demand for diamond jewelry remains strong in the U.S., which accounts for nearly 50% of world consumption, new markets such as India and China are likely to spearhead continued growth. In addition, new social and governmental initiatives have affected how the entire industry conducts business. Source: GIA @topic:8


Title: Prominent Growth Planes Observed in HPHT-Processed CVD Laboratory-Grown Diamonds Abstract: Figure 1. Face-up images of four CVD laboratory-grown diamonds with an eye-visible growth plane. These four diamonds range from 1.81 to 2.51 ct. Photos by Johnny Leung and Tony Leung.
The laboratory-grown diamond industry is ever evolving and improving. With state-of-the-art growth and treatment technology, high-quality CVD diamonds, in terms of clarity and color, are now commonly seen on the consumer market. Laboratory-grown diamonds are occasionally submitted for natural diamond grading services, and recently GIA’s Hong Kong laboratory received a total of 43 undisclosed CVD-grown diamonds treated by high pressure and high temperature (HPHT), ranging from 0.70 to 2.63 ct in weight, from the same client. Laboratory-Grown Diamond Reports were issued for these synthetics, which received E–I color grades and VVS2–I2 clarity grades.
Four samples had a very eye-catching feature—a dark circle or ring at the center when viewed face-up without magnification. The ring appeared to be a thick grayish layer at the culet when viewed from the pavilion (figure 1). As the extraordinary feature looked shiny and resembled the separation plane often observed in assembled stones, questions about the true identity of these samples were raised.
Microscopic examination of these four samples revealed some interesting findings. There was a textured plane almost parallel to the table facet, each with a different appearance (figure 2): fine clouds all the way across; ripple-like waves with some “holes” (colorless areas); a mixture of both; and a ripple-like plane that was not visible all the way around.

Figure 2. Visible planes with different textures: fine clouds (top left, field of view 3.83 mm) and wave ripples (top right, field of view approximately 3 mm). Colorless “holes” observed in a ripple-like plane under the microscope (bottom left, field of view 3.83 mm) and in immersion (bottom right). The blue color in the top left photo is due to a different white balance to emphasize the texture. Images by Billie Pui Lai Law (top left, top right, and bottom left) and Johnny Leung (bottom right).
An additional 26 samples had visible grayish/brownish planes either at the pavilion, which were much less prominent, or at the pavilion viewing through the table. Eight of these additional samples had a plane at an angle to the table facet. The plane appeared as a line with no color difference when immersed in water and viewed in a parallel direction to the growth plane. All 43 samples generally showed a banded and cross-hatched strain pattern when viewed with crossed polarizers (figure 3).

Figure 3. A banded strain pattern seen across the visible plane. Photo by Billie Pui Lai Law; field of view 11.45 mm.
Spectroscopic analysis of the 43 samples yielded very similar results. They were either type IIa or type IIb and had a very strong silicon vacancy doublet peak (736.5 and 736.9 nm) in their photoluminescence spectra, typical of CVD-grown diamonds. PL spectra were also collected at the table and at the pavilion somewhere between the growth plane and the culet for the samples with a very prominent growth plane, but the data did not show any critical differences. The most diagnostic test was DiamondView imaging, as all 43 displayed very distinct growth layers (figure 4). It also revealed the HPHT treatment history that the CVD diamonds had experienced.

Figure 4. DiamondView imaging provided evidence of CVD growth. Images by Billie Pui Lai Law.
The uniformity of the growth layers observed in DiamondView imaging and under crossed polarizers, together with the immersion test, showed no evidence of assembly and therefore excluded the possibility of a doublet. The color making the growth plane visible is believed to come from the non-diamond carbon deposited between two growths. It could not be removed by the post-growth HPHT treatment. Source: GIA @topic:4


Title: Yellow and Orange Diamonds, New Identification Techniques, and the Chronicles of Chivor Abstract: Welcome to the Summer Gems & Gemology! This issue is packed with informative contents, including the characteristics of yellow and orange diamonds, new gem identification techniques, and the colorful history of the Chivor emerald mine.
“In the world fancy-color diamonds, yellow diamonds are by far the most common while those with an unmodified orange hue are among the rarest.”
In the world of fancy-color diamonds, yellow diamonds are by far the most common while those with an unmodified orange hue are among the very rarest (kudos to Robert Weldon for capturing them on the cover). Both yellow and orange diamonds owe their color to nitrogen-related defects. In the lead article, a GIA team led by Christopher M. Breeding and Sally Eaton-Magaña presents the last in their series documenting the gemological and spectroscopic properties of fancy-color diamonds.
Next, Colin McGuinness and colleagues present a luminescence imaging technique developed by De Beers Group Technology that can quickly and easily distinguish colorless and near-colorless natural diamond from laboratory-grown diamond. One marker can identify more than 99% of natural type Ia and type IIa diamond. A pair of newly developed instruments expand on the technology of the DiamondView instrument introduced by De Beers a quarter of a century ago.
In the third article, Karl Schmetzer and coauthors conclude a sweeping two-part series chronicling the Chivor emerald mine in Colombia. This article examines events from 1924 to 1970, when the mine was principally owned by an American firm. While the early era was marked by stock market speculation and scandal, there were also highly productive periods at the fabled mine.
Optical brightening agents for pearls, which are separate from bleaching and maeshori treatments, are the topic of the fourth article. A team of GIA researchers led by Chunhui Zhou provides a fluorescence spectroscopy technique for confidently separating optically brightened pearls from non-brightened pearls.
In the final article, a team of researchers led by Kong Gao of NGTC in China provide a means of discriminating the geographic origin of dolomite-related nephrite from the four most important sources worldwide. This determination relies on hydrogen and oxygen stable isotope ratios. Isotope analysis is an emerging method in gemological research.
As always, our regular columns offer an illuminating array of insights. Highlights of the Lab Notes section include an exceptional purple sapphire from Montana, a vivid blue hemimorphite cabochon resembling Paraíba tourmaline, and interesting observations on an irradiated blue diamond and a rough diamond crystal with irradiation staining. Micro-World reveals rare and breathtaking observations from the inner landscapes of gemstones, including what is believed to be the first reported inclusion of fluorophlogopite in spinel (or any other gem material). In Gem News International, you’ll find a characterization of purplish pink diaspore reportedly from a new deposit in Afghanistan, a look at the cutting and identification of the world’s largest faceted kunzite, a study of petrified woods from the Russian Far East, and much more.
On a final note, the G&G Facebook group (www.facebook.com/groups/giagemsgemology) is now more than 10,000 members strong. We thank you for your participation and your continued interest in the journal. Source: GIA @topic:4


Title: Carnegie Scientists Use Diamond Presses to Study Planet Formation Abstract: The Carnegie Institution’s Geophysical Lab uses high-pressure, high-temperature (HPHT) presses for a variety of purposes, including geological research into the earth and other planets, as well as exotic new materials for technological applications. Here, scientists Steve Shirey and Stevce Stefanoski prepare to load an experiment into of one of the lab’s multi-anvil presses. Duncan Pay © GIA, courtesy Carnegie Institution of Washington.

                      To gemologists, the high-pressure, high-temperature (HPHT) press speaks of synthetic diamond growth or newfangled methods of diamond color treatment.

For Valerie Hillgren, a research scientist at the Carnegie Institution of Washington’s Geophysical Laboratory, the presses that create these conditions are a means to another end: studying how the terrestrial planets of our solar system might have formed.

We’re standing in a large machine room Geophysical Laboratory with Hillgren and her colleague, Dr. Steven Shirey, from the Carnegie’s Department of Terrestrial Magnetism.

The air rings with the hum of heavy equipment and the rhythmic tick of incremental pressure building in a myriad of pipes. The smell of oil is strong, and dials line the walls. Around us are four enormous multi-anvil presses—each the size of a small Volkswagen—that researchers use to simulate conditions deep inside the earth or other planets. Each apparatus can bring to bear pressures equal to that at the core of the planet Mercury.

The interiors of these machines can accommodate pressures measured in gigapascals (GPa). They’re capable of 25 GPa, the equivalent of 700 km (435 miles) beneath the earth’s surface. Pressures of this magnitude allow scientists to study rock-forming systems in the earth’s mantle.

Although this sounds impressive, it’s only a fraction of the depth of the earth’s layers: the center of the earth’s core is 6,378 km (3,963 miles) below the surface.

“When you want to start looking at things that happen in the deep earth, well, 25 GPa only gets you to the top of the lower mantle,” says Hillgren.

Just for comparison, the pressure inside the earth’s core is 360 GPa or 3.64 million bar. The pressure at the earth’s surface, about 1 bar, equals 0.0001 GPa.

	HPHT Research

	Valerie Hillgren was able to combine the two subjects she loved, astronomy and geology, into a dream job: studying planetary geology at Carnegie using the Geophysical Lab’s HPHT presses. Pedro Padua © GIA, courtesy Carnegie Institution of Washington.
Hillgren’s work focuses on separation of a planet’s mantle and core, specifically when they start to differentiate into metal-rich and silicate-rich portions. “What we’re looking at is how the chemistry of different elements is partitioned between the mantle and the core of a planet, and how that happens under higher pressure,” she says.

Hillgren tells us that the experiments can run anywhere from a few minutes to a day or two, depending on the objectives. “We usually start out with mixtures of oxides and metals in proportions that we think are reasonable for the compositions of the planets,” she explains, “and we put them inside the capsule and heat it up.”

After sufficient heat and pressure, she notes, “It separates into a metal portion and a silicate portion, and then we recover that and study the chemistry.”

View Gallery

	In this sequence of photos, you’ll take a glimpse at the inner workings of the Geophysical Lab’s multi-anvil presses.
Hillgren adds, “We look at what our results tell us about the materials that must have formed the planets, what sort of conditions must have existed, when the cores segregated, and perhaps also what has happened after the segregation of the core.”

“One of the things we can look at to understand that process is the chemistry of the mantle, which leaves a signature behind from when the metal segregates,” she continues. “So we just try to recreate that by using these presses, here, looking at the conditions in the deep interiors of the planets.”

Currently Hillgren is studying the solar system’s innermost planet: Mercury. “Mercury is a very unusual planet with proportionately a very large metal core compared to other similar terrestrial planets in the solar system—Mars, Earth, and Venus.

“It’s a mystery—why does Mercury have such a large core? Is it the innate chemistry of the planet, or is it some process that happened after the planet formed?”

Hillgren and her colleagues consider the compositions of the various meteorites as potential starting materials for planetary formation: “We have lots of different meteorite classes, and we’re looking to see if any of those make sense to be the starting materials that Mercury was made out of.”

	The Chergach meteorite, of which this is a part, fell in Mali in 2007. It’s representative of a class of meteorites called chondrites. These stony (non-metallic) meteorites have not been modified by melting and are considered pretty close to the starting material for many of the planets. Valerie Power © GIA, courtesy H. Obodda Precious Gems and Minerals.
She explains that they’ll experiment with different pressure and temperature conditions. “If we apply different conditions to materials, do we end up with different compositions of mantles and cores? We look at not just the earth, but other planets.”

We ask Hillgren which presses she uses. With a laugh she tells us she uses them all. “Depends on what pressure I want to go to! Right here is a piston cylinder, which can go to 2–3 GPa—which would be very shallow. The other presses are multi-anvils, where we can go up to 25 GPa if you want to go deeper.

Hillgren says the interesting thing about Mercury is its core-mantle boundary. “So if you want to look at the segregation of the core,” she explains, “it’s only 7 GPa, which makes it a very easy and accessible planet to study using these presses with very routine methods.”

Finally, we ask Hillgren how she became interested in this field. She feels very fortunate things turned out the way they did: “When I was young, I was always interested in astronomy, and once I got into college, I became very interested in geology…In my last year in undergraduate school, they had a course on planetary geology, and for me it was just combining two things that I really loved…outer space and geology.”

To see more on high-pressure research at the Carnegie Institution of Washington’s Geophysical Lab, visit: https://www.gl.ciw.edu/research/high_pressure_research

	Other High-Pressure Research at Carnegie
According to Dr. Steven Shirey, the Carnegie Institution’s Geophysical Lab has long been a leader in high-pressure research. It started with experiments in the early 1900s at much shallower pressure and higher temperature to look at rock-forming mineral systems in the earth. Scientists were looking to gain a basic understanding of their thermodynamics to work out how rocks and magmas form in the deep earth.

Shirey tells us there hasn’t been a lot of work on natural diamonds at the Geophysical Lab, but that there’s likely to be more in the future. Much of the lab’s work has been focused on synthetic diamonds—especially CVD-grown—and experiments into exotic new materials for use as semiconductors and other technological applications.

	Early Research Using the Piston Cylinder
Research in the 1960s used the piston cylinder, a simpler type of high-pressure device. As Shirey describes it, “You have a cylinder, that’s the confining jacket, and there’s an inner ring and then a subsidiary ring and then another ring. These confinement rings are assembled at pressure, so that they can handle the potential expansion as you push the piston.”

	Piston Cylinder

	Dr. Steven Shirey explains the Geophysical Lab’s early forays into the realm of high-pressure, high-temperature research, beginning with the earth’s rock-forming systems.
“The sample goes in a cylinder of various materials with a central region,” he says. “It’s usually some sort of capsule made out of a noble metal—could be gold or platinum, or it could be graphite. And then there’s a bunch of compressible components—could be salt or pyrophyllite—and then a jacket around that.”

Pyrophyllite is a phyllosilicate mineral composed of aluminum silicate hydroxide—Al2Si4O10(OH2)—that’s widely used in high-pressure experiments, both as a gasket material and as a pressure-transmitting medium.

Shirey explains that a resistance heating system goes in through the holes in the cylinder: “When you compress the whole thing, you get the pressure from compression and you get the heating from the application of a voltage across this resistance.”

These devices can get into the 50 kilobar (5 GPa) range or thereabouts, which would be about 150 km (93 miles) inside the earth, he says: “That’s about the top end of a piston cylinder.”

That’s miniscule compared to a multi-anvil press, Shirey says, gesturing at the larger apparatus behind him: “Nonetheless, the early problems attacked with the piston cylinder were basic things—the melting relations of the mantle, the kinds of melts that were formed, and this would simulate a lot of the experimental work you’d see in mantle xenoliths that are brought up in kimberlites.”

	Multi-Anvil Presses
Any work done on natural diamond formation would require use of the multi-anvil presses, which can hold larger volumes of experimental materials, Shirey says. Just like the piston cylinder, scientists can apply a voltage across a resistance to heat the ample to high temperatures to replicate those inside the earth or another planet.

	Multi-Anvil Presses

	In this video, Dr. Shirey shows us the Carnegie lab’s multi-anvil presses and explains their advantages over earlier devices like the piston cylinder.
But multi-anvil presses work in a different way, he says: “Here we have these opposed, cubic pieces that float in a larger containment, and then inside them are boron nitride cubes that then have a cutout in the corner and the sample goes in the corner of the cubes.”

Shirey holds the octahedral sample holder—made from a compound of magnesium and chromium oxides (MgO and Cr2O3)—between his thumb and forefinger. It nests at the center of the eight cubes that might be composed of either boron nitride or tungsten carbide. It’s rather tiny, given the bulk of the press. A diagonal hole pierces the sample holder, and that’s where the actual experiment occurs. Shirey tells, without a hint of irony, that this is a “larger-volume apparatus.”

“The virtue of these guys is that they can go to much higher pressures with a volume that’s big enough to put into an electron microprobe to do a pretty good analysis.” Source: GIA @topic:7


Title: Coronavirus May Cut Chinese Demand, Diamond Companies See Better Times Abstract: The coronavirus epidemic prompted the management of the Hong Kong Gem and Jewellery Show to move the March event to May, fearing the large crowds it draws may spread the disease. Photo by Russell Shor/GIA

Images of empty commercial streets and shopping malls in China fill the news as the coronavirus spreads throughout the country. The management of the Hong Kong Gem and Jewellery Show has moved the event from early March to mid-May because of concerns about the epidemic. In addition, the Hong Kong government has cut off 10 of 13 entry points at the Hong Kong-mainland border and many flights have been suspended in an effort to slow the spread of the disease.
The impact of this will likely cut deeply into the economies of mainland China and Hong Kong, where stock markets have plunged more than 8% after reopening following the New Year’s break. Mainland tourism accounts for about 70% of Hong Kong’s retail business. Retailers, including jewelry sellers Chow Tai Fook and Pandora, have shut stores throughout the country.
While it is too early to get specific data from retailers and suppliers, gold dealers said demand from China hit “record lows” in the last two weeks of January ‒ usually a time when the New Year boosts sales. On the mainland, the government extended the New Year holiday to keep people home – and home they stayed, with city streets deserted, even in the capital of Beijing. The government has injected some $22 billion into the economy in the form of credit to tide it through the crisis.
The World Health Organization predicts that the virus epidemic is only in its early stages and that it will spread well beyond the affected areas of the country. According to economists, this could have a profound effect on the world economy. Beyond its leading consumer market role, China is an integral part of the global supply chain and prolonged disruptions there could adversely affect many markets around the world, especially electronics which, in time, could slow world economic growth several percentage points. Hyundai, the Korean automaker, announced that it is closing its factories because they have run out of key components from China.
DIAMOND ROUGH
The major diamond producers believe the crisis in the rough market ‒ oversupplies bringing softening prices and cutbacks in bank credit ‒ has eased. Some diamond cutting firms who find their credit restricted and cash flow spotty aren’t so sure, but for now De Beers, Alrosa and others have reopened the spigots.
De Beers’ January cycle of $545 million was 9% higher than the first sale of 2019 and the highest in nine months, reflecting the company’s confidence that the supply overhang that depressed prices and demand last year has abated. Alrosa has not yet announced the results of its Jan. 17-21 sales, but the company stated it believes the diamond market is close to “alignment.”
De Beers’ CEO Bruce Cleaver said in a statement that demand for rough diamonds was up following the fourth quarter holiday season because clients needed to restock. De Beers’ sales plunged by 25% last year.
The company, however, clearly has no plans to go back to business as usual. It has been widely reported that De Beers will be shaking up its client list at the end of the year. While few details have been forthcoming, it is probably a 2020 version of its “fewer, stronger, hands” policy that it adopted following the 1980s crisis, with goods that flow more toward dealers without large factories to support, rather than manufacturers.
De Beers’ criteria for becoming a client, which it calls “demonstrated demand,” basically requires firms to purchase a contracted quantity of rough each cycle during the length of the agreement. Many clients, however, had to defer purchases last year, or even sold goods back to De Beers, because they were unprofitable to cut.
Indeed, the 2019 crisis was hardly the first crisis set off by overstocking ‒ it also happened in 2015 and, of course, 2009-2010, when the world economy itself was in crisis. Even before then, many analysts believed that there was an excess of diamond manufacturing capacity of 20% or more, but with the banks supplying credit, manufacturers could afford to store the excess stones.
Alrosa, the world’s largest producer by volume, stockpiled diamonds last year instead of trying to sell them to over-stretched clients – its rough inventory increased by 33%, according to Alrosa’s latest earnings announcement.
The company’s sales were down 26% by value at $3.27 billion, and 12.4% by volume (33.4 million carats) last year. Its inventory grew by five million carats to 22.6 million – or two-thirds of its 2019 sales volume. The size of Alrosa’s inventory suggests that, ironically, it has taken De Beers’ former role of market custodian, stockpiling goods in slow times.
Rio Tinto, the third largest diamond producer, announced that its diamond production declined 8% to 17 million carats last year as the company shifted production to lower grades in both Diavik (Canada) and Argyle (Australia) – often a strategy to avoid over-production.
While Rio Tinto’s Argyle Mine is known for the few hundred carats of fancy color pink diamonds it produces each year, the majority of the 14 or so million carats it produces are small, lower quality stones that have been under considerable price pressure.
It is encouraging, however, that Rio Tinto wants to stay in the diamond business after Argyle closes at the end of this year and Diavik closes in 2023. It wants to take a 60% stake in the Canadian Orion South project, which is a producer of higher-value diamonds. The deposit could be an important source of Type IIa colorless diamonds.
GOLD JEWELRY
Weakening currencies and slowing economic growth pushed demand for gold jewelry to its lowest point in a decade during the final quarter of 2019, according to the World Gold Council.
The group reported demand in India fell 17% in the final quarter of the year, compared to the same period of 2018. Chinese demand also fell 10% as trade disputes with the U.S. and rising prices took their toll. In addition, young buyers have been shying away from plain gold toward more fashion-oriented designs that use much less of the metal, according to the Council.
In the U.S., demand for gold rose 2%, but that was not enough to offset the declines in India and China.
Global demand for gold from all industries – electronics, financial, medical and investment ‒ fell 1% for the year. Source: GIA @topic:8


Title: Large HPHT-Grown Synthetic Diamonds Examined in GIA’s Hong Kong Laboratory Abstract: These two large synthetic diamonds were produced using HPHT growth methods by the Russian firm New Diamond Technology. The 4.30 ct specimen on the left has D color and SI1 clarity. On the right is a 5.11 ct sample with K color and I1 clarity. Photo by Ming Yin Poon.

              Over the last decade, the jewelry industry has seen rapid improvement in the quality of synthetic diamond grown by the CVD (chemical vapor deposition) method. Colorless and near-colorless CVD synthetics with sizes up to 3.04 ct, with I color and SI1 clarity, have been reported. GIA’s Hong Kong laboratory recently examined two large synthetic diamonds created using the HPHT (high-pressure, high-temperature) method that demonstrated parallel progress in the two growth technologies. These samples, shown above, were produced in Russia by New Diamond Technology.

The first was a 4.30 ct cushion shape with D color and a clarity grade of SI1, based on three small clusters of metallic inclusions. The other was a 5.11 ct cut-cornered rectangular modified brilliant. It had K color and a clarity grade of I1, the result of a few metallic inclusions and two small fractures in the girdle area. Neither one showed reaction to long-wave UV radiation. When they were exposed to short-wave UV, a medium to strong green-yellow fluorescence was observed. Both showed strong yellow-green phosphorescence lasting more than 20 seconds. One noteworthy feature was the absence of pinpoint inclusions, which are common in HPHT synthetic diamonds and often distributed throughout the crystal.

Absorption spectra in the infrared region demonstrated these were type II diamonds, with no absorption band detected in the one-phonon region (approximately 1350–1000 cm–1) where nitrogen impurities occur. A very weak 2800 cm–1 band was attributed to trace substitutional boron. A higher boron concentration was recorded in the D-color synthetic diamond (7 ± 1 ppb, compared to 1.2 ± 0.2 ppb). Photoluminescence spectra collected at liquid-nitrogen temperature with varying laser excitations revealed an emission doublet at 736.6/736.9 nm from the silicon-vacancy defect, and an 882.7/884.4 nm doublet from the well-known Ni-related defect. Very weak emissions from nitrogen-vacancy centers at 575.0 and 637.0 nm were detected only in the K-color sample. Besides metallic inclusions, another important identification feature of HPHT synthetics is fluorescence. Typical fluorescence patterns showing multiple-sector growth were observed in both samples.

These two diamonds were disclosed as HPHT synthetic when submitted for examination. Tested using the GIA DiamondCheck device, both were referred for further testing. Gemological observations and spectroscopic features confirmed they were HPHT synthetics.

Examination of these improved HPHT synthetic diamonds, the largest synthetic diamonds produced by any method that GIA has examined so far, demonstrated significant progress in this growth technology. In addition to their use as gem materials, crystals of this size have many potential industrial applications. Source: GIA @topic:4


Title: Two Large CVD-Grown Synthetic Diamonds Tested by GIA Abstract: Figure 1. The I-color 3.23 ct round on the left (9.59–9.61 × 5.83 mm) and H-color 2.51 ct round on the right (8.54–8.56 × 5.43 mm) are the largest CVD synthetic diamonds GIA has tested. Photos by Jian Xin (Jae) Liao.

	The quality and size of near-colorless and colorless synthetic diamonds grown by chemical vapor deposition (CVD) have rapidly improved in recent years due to advances in growth techniques and the introduction of post-growth decolorizing treatments. Near-colorless CVD synthetics have now passed the three-carat threshold. In September 2015, a 3.09 ct sample (I color, VS2 clarity) of unknown provenance was submitted to HRD Antwerp. This was preceded by Pure Grown Diamonds’ announcement of a 3.04 ct synthetic (I color, SI1 clarity) in December 2014.

	GIA’s New York laboratory recently tested two large CVD synthetic diamonds (figure 1) submitted for grading services. These synthetics, weighing 2.51 and 3.23 ct, are the largest CVD-grown diamonds GIA has examined to date. The results of the examination underscore the continued improvements in CVD synthetic diamonds.

	The 2.51 and 3.23 ct round brilliants received H and I color grades, respectively. Microscopic examination revealed pinpoint and black inclusions in both, while small fractures along the girdle were only observed in the 2.51 ct round (figure 2). The 3.23 ct synthetic contained a small black inclusion measuring approximately 125 µm. As a result, SI1 and VS2 clarity grades were given to the 2.51 and 3.23 ct samples, respectively. Both revealed irregular stress patterns with high-order interference colors when viewed under cross-polarized light (figure 3), indicating high levels of strain.

Figure 2. Left: These pinpoint inclusions were observed in the 2.51 ct synthetic diamond. Right: A small black inclusion measuring approximately 125 µm was observed in the 3.23 ct sample. Image widths 4.72 mm (left) and 6.27 mm (right). Photomicrographs by Caitlin Dieck.

Figure 3. Irregular stress patterns were observed under the microscope with cross-polarized light. Both the 2.51 ct (left) and 3.23 ct (right) synthetic diamonds showed high-order interference colors. Image widths 5.76 mm and 6.27 mm, respectively. Photomicrographs by Caitlin Dieck.

	The synthetics showed weak orange fluorescence to conventional short-wave UV and were inert to long-wave UV radiation. Exposure to the deep UV radiation ( 230 nm) of the DiamondView revealed an overall strong red-pink fluorescence attributed to nitrogen-vacancy centers with dislocation bundles that fluoresced violet-blue (figure 4), followed by weak greenish blue phosphorescence. Both samples were characterized by a layered growth structure, suggesting that the crystals were grown using a multi-step technique to maximize their volume. The sharp boundaries between the different growth layers are a result of changes in the fluorescent impurity uptake during the starting, stopping, and restarting of growth. These images clearly revealed that at least five growth layers were applied to produce these large crystals. The patterns suggest that the table of the 2.51 ct samples was cut parallel to the growth layers, while the table of the 3.23 ct synthetics was cut at an angle to the growth layers. The dislocation bundles are seen to propagate through the different growth layers. The formation of the two blue bands of highly concentrated dislocations crossing the table of the 2.51 ct specimens is not understood.

Figure 4. DiamondView imaging of both samples revealed strong red-pink fluorescence superimposed with dislocation patterns that fluoresced violet-blue. A layered growth structure indicating start-stop growth was clearly observed on the pavilion of both. The orientation of the layers reveals that the 2.51 ct sample (top) was cut with its table approximately parallel to the growth plane, whereas the layers intersect the table facet in the 3.23 ct sample (bottom). Images by Caitlin Dieck.

	Infrared absorption spectroscopy in the mid-IR range (6000–400 cm–1) showed no major nitrogen-related absorption in the one-phonon region, which classified both samples as type IIa. No hydrogen-related defects were detected, either. UV-Vis-NIR absorption spectra collected at liquid-nitrogen temperature revealed a smooth increase in absorption from the infrared region to the high-energy end of the spectrum, with a 737 nm peak in both samples and a small absorption peak at 596 nm in the 3.23 ct synthetic. The 737 nm peak is an unresolved doublet at 736.6/736.9 nm attributed to [SiV]–. This center is often inadvertently introduced during CVD growth (P. Martineau et al., “Identification of synthetic diamond grown using chemical vapor deposition (CVD),” Spring 2004 G&G, pp. 2–25; W. Wang et al., “CVD synthetic diamonds from Gemesis Corp.,” Summer 2012 G&G, pp. 80–97) but is rarely observed in natural diamonds, especially using absorption methods. The 596 nm feature is particularly useful for identification purposes, as it has only been reported in CVD synthetic material (Martineau et al., 2004).

	Photoluminescence (PL) spectra acquired with 514 nm laser excitation at liquid-nitrogen temperature revealed a doublet at 596/597 nm, nitrogen-vacancy centers at 575 [NV]0 and 637 [NV]– nm, and [SiV]– at 736.6/736.9 nm for both samples, with the [NV]0/– luminescence dominating. The strength of the [NV]0/– centers was consistent with the red-pink fluorescence colors (figure 4). Although the 596/597 nm doublet is not thought to arise from the same center as the 596 nm feature seen in the absorption spectrum of the 3.23 ct sample, it has only been detected in CVD synthetics, thus revealing the samples’ CVD origin (Martineau et al., 2004). The doublet also indicated that the samples had not undergone post-growth HPHT (high-pressure, high-temperature) processing to improve their color, as the treatment would have removed this feature.

	The distribution of [SiV]– centers was investigated through PL mapping of the 736.6/736.9 nm doublet at liquid-nitrogen temperature using 532 nm laser excitation (figure 5). The distribution was different between the two samples, forming patterns that corresponded directly with their DiamondView images (figure 4). For the 2.51 ct sample, the [SiV]– luminescence decreased along the bands with higher concentrations of dislocation bundles. This may indicate that there are fewer [SiV]– centers in this region, or an increased concentration of defects (either structural or impurity-based) that effectively quench the [SiV]– luminescence. Where the growth layers intersect the table in the 3.23 ct sample, the [SiV]– luminescence appeared to be highest at the start of a layer’s growth, decreasing as the growth progressed. This could mean that the concentration of silicon in the growth gas fell over time, or that the concentration of defects that may quench the [SiV]– luminescence increased during growth. Notably, the concentration of dislocations increased as growth progressed.

Figure 5. PL [SiV]- distribution map maps were collected with 532 nm laser excitation. Left: Less luminescence from [SiV]- centers is observed in two broad bands on the 2.51 ct sample. Right: More intense [SiV]- luminescence is found at the diamond layer boundaries in the 3.23 ct sample. Images by Lorne Loudin.

	Analysis of these two large samples demonstrates that high-quality CVD synthetic diamonds can be produced even without post-growth decolorizing HPHT treatment, marking a significant improvement in CVD growth. Using advanced spectroscopic and fluorescence imaging technologies, it is nevertheless possible to detect low concentrations of impurity centers, allowing conclusive determination of these samples’ synthetic origin. GIA is monitoring the development of laboratory-grown diamonds and conducting research to ensure that we can continue identifying every single synthetic diamond. Source: GIA @topic:4


Title: Natural Colorless Type IIa Diamond With Bright Red Fluorescence Abstract: Figure 1. This 0.40 ct, D-color type IIa round brilliant diamond showed very bright red fluorescence due to strong emission peaks from the nitrogen-vacancy centers. Photo by Nuttapol Kitdee.

The nitrogen-vacancy (NV) center is produced in nitrogen-bearing diamond through the combination of a single nitrogen atom and a vacancy. It can exist in neutral (NV0) and negatively charged (NV–) states. Using photoluminescence (PL) spectroscopy, NV centers can be detected by the occurrence of zero-phonon lines (ZPL) at 575 nm for NV0 and 637 nm for NV–. In natural type IIa diamonds, the emissions of NV centers are usually weak, and the relative intensity of NV0 (575 nm) is typically stronger than that of NV– (637 nm). As a result, the vast majority of natural type IIa diamonds show blue fluorescence, attributed to the occurrence of defects such as N3 or dislocations, when excited by the short-wave UV radiation of the DiamondView. Recently, however, the Bangkok laboratory examined a natural colorless type IIa diamond that showed very bright red fluorescence due to high concentrations of NV centers.

This 0.40 ct round brilliant diamond received a D color grade and an SI1 clarity grade based on surface-reaching fractures at the girdle and on the pavilion (figure 1). The infrared absorption spectrum confirmed a type IIa diamond with no measurable defect-related absorptions. Microscopic examination with cross-polarized light revealed a relatively strong tatami strain pattern with a weak interference color (figure 2). Further examination with the DiamondView showed that this stone exhibited an unusual red fluorescence (figure 3), similar to that of nitrogen-doped CVD synthetic diamonds. However, the DiamondView images revealed dislocation networks of typical natural type IIa diamond along with a tree-ring growth pattern, which is very rare for natural type IIa diamond but typical for natural type Ia diamond.

Figure 2. Viewing the diamond under cross-polarizing filters revealed a tatami strain pattern with a weak interference color, a characteristic of natural growth. Photo by Charuwan Khowpong; field of view 3.1 mm.

Figure 3. DiamondView images of the 0.40 ct diamond showed red fluorescence, which is unusual for natural type IIa stones. This red fluorescence was related to the intense emissions of the NV centers. Also observed was a dislocation network typical of natural type IIa diamond, along with a tree-ring growth pattern. Photo by Wuyi Wang.
In order to detect any possibility of treatment, we employed PL spectroscopy at liquid nitrogen temperature with several laser excitations. With 514 nm laser excitation, the PL spectrum revealed very strong emission peaks from NV0 (575 nm) and NV– (637 nm) (figure 4). This is very rare in natural type IIa diamonds. The higher intensity of the NV0 emission was observed. For this diamond, short-wave UV excitation close to 230 nm was very effective in exciting fluorescence from the NV–, which has a ZPL at 637.0 nm and its strong side bands at longer wavelengths. Due to the relatively high concentration of the NV– defect, strong red fluorescence was observed.

Figure 4. The photoluminescence spectrum at liquid nitrogen temperature using 514 nm
laser excitation displayed strong emission peaks at 575 and 637 nm due to NV0 and
NV– centers, respectively. In natural type IIa diamonds, the intensity of NV centers is
usually weaker than the diamond Raman peak at 552 nm.
Both spectroscopic and gemological features clearly indicated a natural diamond. The excellent color and the red fluorescence, which is rare for a natural colorless type IIa diamond, make this a notable stone. Source: GIA @topic:4


Title: CVD Synthetic Diamond Over 5 Carats Identified by GIA Abstract: Figure 1. This 5.19 ct CVD synthetic diamond (10.04 × 9.44 × 6.18 mm, with J-equivalent color and VS2-equivalent clarity) is the largest GIA has identified to date. Photo by Johnny Leung and Tony Leung.

Chemical vapor deposition (CVD) technology has accelerated over the last several years, and the rapidly improving techniques have produced large, high-quality near-colorless and colorless synthetic diamonds. Two samples over 3 carats were reported in early 2016 as the largest CVD synthetics. GIA recently tested a CVD-grown synthetic diamond that weighed over 5 carats, marking a significant milestone.

The 5.19 ct cushion modified brilliant measuring 10.04 × 9.44 × 6.18 mm (figure 1) was submitted to GIA’s Hong Kong laboratory for grading service. The stone was not disclosed as a synthetic diamond. Using the lab’s standard screening and testing processes, it was identified as CVD synthetic. Following examination, a GIA Identification Report was issued and the stone was inscribed on the girdle with the report number and the words “Laboratory Grown,” following GIA’s protocols for undisclosed synthetics.

This is the largest CVD synthetic diamond GIA has examined to date, and the largest reported in the jewelry industry. It had J-equivalent color grade and VS2-equivalent clarity, comparable to a high-quality natural counterpart. Natural-looking internal inclusions such as needles and clouds were the major features (figure 2). Strong graining and a fracture in the table were also clearly observed under the microscope. It is worth noting that black inclusions, often contained in synthetic diamond, were not found in this CVD specimen, which could have been mistakenly identified as natural based on microscopic examination alone. This case therefore highlights the importance of using advanced spectroscopic instruments as well as conventional gemological techniques to ensure an accurate identification.

Figure 2. Needles and pinpoints were the major internal features. Black inclusions, a
common feature of CVD synthetic diamond, were not observed. Photo by Billie “Pui
Lai” Law.
Viewing the sample under a binocular microscope with cross-polarized light revealed irregular birefringence patterns with high-order interference colors, a common feature of CVD synthetic diamond (figure 3). Fluorescence images under the short-wave UV radiation of the DiamondView showed strong red fluorescence with irregularly distributed areas of violet-blue (figure 4). The images also revealed a layered growth structure, indicating a start-stop cycling growth process typical of CVD synthesis. Up to six growth layers basically parallel to the table were identified from the fluorescence features. These multiple growth segments make it possible to grow such a thick sample.

Figure 3. Microscopic examination between crossed polarizers revealed high-order
interference colors, attributed to strong lattice dislocation. Photo by Billie “Pui Lai” Law.

Figure 4. Fluorescence imaging from the DiamondView showed strong red fluorescence
with bundles of violet-blue. Up to six growth layers basically parallel to the table were
revealed. Photo by Billie “Pui Lai” Law.
Infrared absorption spectroscopy identified the sample as type IIa. Except for a very weak absorption at 1332 cm–1, no other absorption features (such as hydrogen-related defects) were detected. Photoluminescence (PL) spectra were collected at liquid nitrogen temperature with various excitation wavelengths. The SiV– doublet at 736.6 and 736.9 nm, a common feature of both CVD and HPHT synthetics and only rarely seen in natural diamond, was observed using 457, 514, and 633 nm laser excitation, suggesting the sample’s synthetic origin. Spectra acquired with 514 nm laser excitation also showed emissions from NV centers at 575.0 nm (NV0) and 637.0 nm  (NV–), with the NV0 center dominating in intensity (figure 5). The occurrence of a weak emission pair at 596.5 and 597.2 nm, in combination with the absence of H3 emission, unequivocally identified this as an as-grown CVD synthetic diamond. No post-growth annealing had been applied to improve its color appearance.

Figure 5. The photoluminescence spectrum acquired with 514 nm laser excitation
revealed strong emissions from NV centers in addition to emissions from SiV–.
Emissions at 596/597 nm indicated that this synthetic diamond was not annealed
after growth.
CVD synthetics are available from several sources. The gemological and spectroscopic features of this 5.19 ct sample are very similar to those GIA has examined from Washington Diamonds (now known as WD Lab Grown Diamonds). As diamond growth techniques continue to advance, we expect to see more high-quality samples, both in size and clarity. Source: GIA @topic:4


Title: Two Natural Type IIa Diamonds with Strong Phosphorescence and Ni-Related Defects Abstract: Figure 1. DiamondView images of two unusual diamonds (0.18 and 0.30 ct, respectively). Left: Unevenly distributed grayish blue fluorescence and strong blue phosphorescence. Right: Vivid red fluorescence, strong blue phosphorescence, and a dislocation network can be seen in the table. Images by Shi Tang.
Strong phosphorescence under UV excitation is rarely seen in natural diamond and normally limited to hydrogen-rich type Ia or type IaA/Ib chameleons and type IIb diamonds (T. Hainschwang et al., “A gemological study of a collection of chameleon diamonds,” Spring 2005 G&G, pp. 20–35; S. Eaton-Magaña and R. Lu, “Phosphorescence in type IIb diamonds,” Diamond and Related Materials, Vol. 20, No. 7, 2011, pp. 983–989). When seen in other diamond types, an even rarer occurrence, it is shorter and less intense. Recently, the National Gemstone Testing Center (NGTC) in Beijing encountered two natural diamonds that showed extraordinarily strong blue phosphorescence and uncommon fluorescence colors under the DiamondView.

The diamonds weighed 0.18 and 0.30 ct and were both graded as E color. Both were type IIa, with neither nitrogen absorption between 1100 and 1400 cm–1 nor boron-related absorption in their infrared spectra. Magnification and examination with a standard UV lamp showed no abnormal phenomena for natural type IIa diamonds. Instead of the deep blue fluorescence and inert phosphorescence that natural type IIa diamonds typically show in DiamondView imaging, the 0.18 ct diamond emitted unevenly distributed grayish blue fluorescence and strong blue phosphorescence, similar to that of a colorless HPHT synthetic diamond. The 0.30 ct diamond displayed vivid red fluorescence and strong blue phosphorescence, which is unusual for a natural colorless to near-colorless diamond (figure 1). Red fluorescence is rare in natural type IIa diamond and seldom reported (Summer 2016 Lab Notes, pp. 189–190).

Photoluminescence (PL) spectra collected with 532 nm laser excitation at liquid nitrogen temperature revealed something even more interesting. Along with the GR1 center emission at 741 nm typically seen in natural type IIa diamonds, the 883.0/884.7 nm doublet that is related to nickel impurity appeared in both samples’ PL spectra (figure 2). This doublet, often referred to as the “1.40 eV center,” is frequently seen in the {111} growth sectors of HPHT synthetic diamonds produced using Ni-based solvents/catalysts. Ni-related defects are more often seen in natural chameleon and greenish yellow diamonds (W. Wang et al., “Natural type Ia diamond with green-yellow color due to Ni-related defects,” Fall 2007 G&G, pp. 240–243; Summer 2014 Lab Notes, pp. 151–152) but seldom found in colorless to near-colorless natural diamonds (e.g., Spring 2017 Lab Notes, pp. 95–96). For natural diamonds with such strong phosphorescence, the presence of Ni-related emissions is unusual.

Figure 2. PL spectra of the two samples with 532 nm laser excitation. Both showed weak Ni-related doublets at 883.0/884.7 nm and strong NV centers at 575 and 637 nm, as well as the GR1 center at 741 nm.
The PL spectrum of the 0.30 ct sample also presented an extremely strong NV center at 575 nm, compared to the diamond emission at 572 nm, which explained the reddish fluorescence in the DiamondView image. In each sample’s PL spectrum, the relative intensity of NV0 (575 nm) is significantly stronger than that of NV– (637 nm), another sign of natural origin.

Figure 3. The PL spectrum of the 0.30 ct sample emitted with a 532 nm laser, at higher excitation energy. The NV0 center peak is saturated, and emissions at 648 and 776 nm are clearly seen.
Furthermore, when we exposed the 0.30 ct sample to higher-energy excitation with the 532 nm laser to reveal more subtle features, the PL spectrum showed moderately strong emissions at 648/649 nm and 776 nm (figure 3). According to previous research, PL peaks at 648.2 and 776.4 nm are associated with boron in phosphorescing type IIb natural diamonds (Eaton-Magaña and Lu, 2011). Later studies ascribed the 648.2 nm defect to a boron-interstitial complex, while the 776.4 nm peak was assigned to a B-V complex (S. Eaton-Magaña and T. Ardon, “Temperature effects on luminescence centers in natural type IIb diamonds,” Diamond and Related Materials, Vol. 69, 2016, pp. 86–95). These emissions may partly explain the strong phosphorescence of the 0.30 ct sample. Since they were not detected in the 0.18 ct sample, which also exhibited strong phosphorescence—the same is true of other phosphorescent natural IIa diamonds the authors have encountered before—this cannot be the full explanation.

Despite the synthetic-like luminescence color in DiamondView imaging and the Ni-related emissions in the PL spectra, the samples’ Fourier-transform infrared (FTIR) spectra, UV-visible spectra, PL spectra, features observed under the crossed polarizing microscope, and UV reaction indicated that they are natural instead of synthetic. These two samples demonstrated the diversity of luminescence and spectral features found in natural diamond. Their identification also highlights the importance of a comprehensive understanding of diamond origin. Source: GIA @topic:4


Title: One Natural Melee Diamond Found in Large Batch of HPHT Synthetic Melee Abstract: Figure 1. Out of a parcel of 1,102 diamond melee received at GIA’s New York lab for testing, 1,092 were identified as HPHT synthetic melee. Photo by Sood Oil (Judy) Chia and Towfiq Ahmed.

Over the last decade, the production methods used to create synthetic diamond melee have improved substantially, along with the quality of the specimens themselves. The increase in the amount of synthetic melee submitted—both disclosed and undisclosed—to GIA’s laboratories for identification has exponentially increased since GIA began offering its Melee Analysis Service in 2016. Parcels of melee are often submitted with a mixture of naturals and synthetics. Typically, a few synthetics are detected in batches of natural melee diamonds, known in the trade as “salting” (e.g., S. Eaton-Magaña and J.E. Shigley, “Observations on CVD-grown synthetic diamonds: A review,” Fall 2016 G&G, pp. 222–245).
GIA’s New York laboratory received a batch of 1,102 melee diamonds with a total weight of 9.67 carats for the melee analysis service. The tested melee ranged from 0.98 to 1.52 mm in diameter. Preliminary testing using GIA’s fully automated screening device referred 1,093 for further testing, while nine were found to be outside of the service criteria. Further analysis using detailed spectroscopic analysis confirmed 1,092 (figure 1) out of the 1,093 to be HPHT synthetics. Fourier-transform infrared (FTIR) absorption spectroscopy performed on the referred melee revealed an absorption band at approximately 2800 cm–1 from trace boron in the diamond lattice, classifying these melees as type IIb (boron-bearing), typical of HPHT synthetic diamonds. Due to the relatively high concentrations of boron, these melee diamonds showed a clear blue hue, which is very different from most of the melee diamonds we have tested.
Further examination using photoluminescence (PL) spectroscopy showed no detectable peaks of nickel, often a catalyst used to grow HPHT synthetic diamonds (e.g., Spring 2017 Lab Notes, pp. 95–96). These spectra were in fact atypical of HPHT synthetic diamonds. Distinctive HPHT growth patterns were observed in the DiamondView (figure 2) along with strong phosphorescence following exposure to short-wave UV radiation (figure 3).

Figure 2. This diamond shows characteristic growth patterns of HPHT-grown material. Photo by Stephanie Persaud.

Figure 3. These HPHT-grown synthetic diamond melee, from the parcel of 1,102 specimens, display strong phosphorescence following exposure to short-wave UV radiation. Photo by Sood Oil (Judy) Chia and Towfiq Ahmed.
One sample out of 1,093 was confirmed as a natural diamond. Infrared absorption spectroscopy indicated this stone was type Ia, with a hydrogen peak at 3107 cm–1. DiamondView imaging displayed a typical blue fluorescence and no detectable phosphorescence, both typical for a natural type Ia diamond.
It is interesting to note that only one natural was found in this parcel of melee. This has been the largest percentage of undisclosed synthetic melee that GIA has seen. The majority of the HPHT synthetic melee had no detectable traces of Ni, demonstrating the importance of advanced testing to identify these melees. Source: GIA @topic:4


Title: Rough Diamond Crystal with an Unusual Coating of Fake Green “Radiation Stains” Abstract: Figure 1. This 6.49 ct rough diamond with patchy green surface color was submitted to GIA’s Carlsbad laboratory for a Colored Diamond Grading Report. Photo by Diego Sanchez.

Due to their rare occurrence and the environment required to create their color, natural green diamonds are some of the world’s most beautiful and sought-after gems. Most diamonds acquire their color from impurities or defects incorporated into the diamond lattice when the material is hundreds of kilometers deep in the earth’s mantle. But most natural green diamonds are colored by radiation damage that occurs at very shallow depths in the earth’s crust over long periods of time. Commonly accompanying this exposure to radioactive minerals and fluids are surface patches of green or brown color that gemologists call “radiation stains.” These are simply areas of extreme damage to the diamond structure caused by alpha particle radiation. Initially green, they turn brown immediately after exposure to temperatures above 500°C. These surface features indicate that a diamond has been exposed to a source of natural radiation; green stains are commonly associated with naturally colored green diamonds.

Figure 2. The diamond’s patchy green coloration is caused by interlocking platy crystals of chromium oxide, visible with magnification. Photomicrograph by Nathan Renfro; field of view 0.72 mm.

Figure 3. The Raman spectrum (514 nm laser excitation) of the rough diamond’s green coating shows clear peaks from chromium oxide (552 and 613 cm–1) as well as the underlying diamond (1332 cm–1). The specific positions of the chromium oxide peaks suggest the coating has been annealed to ~700°C (Mohammadtaheri et al., 2018).
Recently, GIA’s Carlsbad laboratory examined an interesting attempt to imitate a natural green diamond when a 6.49 ct green crystal was submitted for a Colored Diamond Grading Report (figure 1). The surfaces of the resorbed octahedron were covered by uneven patches of green color. Fourier-transform infrared (FTIR) analysis revealed a typical type Ia diamond with abundant nitrogen and hydrogen impurities. However, the ultraviolet-visible (UV-Vis) spectrum was very unusual and did not show any of the bands that are produced by radiation damage in diamond (e.g., the GR1 defect). Careful examination under magnification found that the green color was not due to radiation stains, but instead to groupings of emerald-green platy crystals, ~40 μm in size, attached to the diamond surface (figure 2). Individual platy crystals could easily be flaked off using tweezers or a pointer probe, but they remained adhered to the surface under normal gem testing situations, including wiping the diamond with a stone cloth. X-ray fluorescence (XRF) analysis indicated high concentrations of chromium, and Raman analysis identified the green plates as chromium oxide (figure 3). The Raman peak positions correlated very well with chromium oxide powder that had been heated to ~700°C to produce a crystallized coating (M. Mohammadtaheri et al., “The effect of deposition parameters on the structure and mechanical properties of chromium oxide coatings deposited by reactive magnetron sputtering,” Coatings, Vol. 8, No. 3, 2018, Article No. 111). A small H1b defect present in the diamond’s FTIR spectrum supports this annealing temperature.
Most colored coatings encountered in the lab are on faceted stones and are pink, orange, red, or blue. The warmer hues are typically created by sputter-coating techniques involving metals and the colder hues by inks or other organic dyes. The use of chromium oxide powder to produce a green coating—along with annealing of the powder to produce crystallized plates that adhere to the rough surface to resemble radiation stains—represents a significant attempt to artificially reproduce the features seen on natural green diamonds. While the unique coating is easily discerned from natural green radiation stains under magnification, this stone is a strong reminder to carefully examine any green diamond, even rough crystals, in order to know exactly what you are buying. Source: GIA @topic:4


Title: Why are Pink Diamonds Pink?GIA Researchers Dive Deep into their Crystal Structure Abstract: These diamonds are from the 2016 Argyle Pink Tender in New York City. Left to right: 0.64 ct Fancy Deep pink oval, 0.75 ct Fancy Intense purplish pink trilliant, 0.91 ct Fancy Vivid purplish pink oval, 1.30 ct Fancy Intense pink heart, 1.35 ct Fancy Intense purplish pink cushion, 0.80 ct Fancy Vivid pink pear, and 0.45 ct Fancy Vivid purplish pink emerald cut. Courtesy of Argyle Pink Diamonds. Photo by Robert Weldon/GIA

Natural pink diamonds are among the most valuable and rare of Earth’s treasures. Top, vivid-colored stones can bring more than $2 million per carat at major auctions. Such prices come from their rarity as much as their beauty – only a tiny percentage of diamonds have pink color, and only a tiny percentage of these have a rich, vivid color.
Pink diamonds created in a laboratory, however, are quite different from most of their natural counterparts. Manufacturers can’t replicate the way the vast majority of these fancy colored diamonds formed in nature, according to GIA researchers.
Employing GIA’s immense database of more than 90,000 natural pink and related colored diamonds graded between 2008 and 2016, GIA researchers Dr. Sally Eaton-Magaña, senior research scientist; Troy Ardon, research associate; Dr. Karen V. Smit, research scientist; Dr. Christopher M. Breeding, senior research scientist and Dr. James Shigley, distinguished research fellow, produced the most detailed and comprehensive gemological analysis of pink diamonds to date, published in the Winter 2018 edition of the Institute’s quarterly journal, Gems & Gemology.

Natural-color pink diamonds are exceptional treasures. The lead article in this issue, based on GIA’s database of more than 90,000 diamonds in the pink, orangy pink, purple, red, and brown color continuum, summarizes their gemological and spectroscopic characteristics. Shown on the cover is the 18.96 ct Winston Pink Legacy, a Fancy Vivid pink emerald-cut diamond that recently sold at auction for more than $50 million. Winston Pink Legacy courtesy of Harry Winston, Inc. © 2018 Christie’s Images Limited
The sample set of 90,000-plus diamonds includes all those submitted to GIA from 2008 to 2016 with pink as a primary color, and also spans the color hue range from red to purple and saturation range from faint to dark, along with brown diamonds, which share a similar cause of color as pink and related stones. Many of those 90,000 diamonds were small, with low color saturation.
This research confirms that the color of 99.5% of pink diamonds comes from distortion in their crystal structure, not from trace elements, such as nitrogen, which causes yellow color in diamonds or boron, which causes blue. In pink diamonds containing nitrogen, the color is generally concentrated within parallel narrow bands called glide planes, lamellae, or pink/brown graining, depending upon the color. These lines are visible under a microscope and cutters orient them perpendicular to the table to maximize body color.
While many color-producing defects can be introduced through laboratory treatment processes, atomic level distortions in a diamond’s crystal structure created by plastic deformation cannot.
“We know that plastic deformation is associated with the vast majority of diamonds with these colors, but we still do not know the actual atomic structure of the defect causing the color,” says Breeding, who notes that the pink color is caused by a broad absorption band centered at 550 nanometer (nm) in spectroscopic analysis. Spectroscopic analysis is an important gemological tool to measure the impurities and other defects within a diamond (and other gemstones) that give rise to specific absorption peaks or bands in the visible spectrum. The researchers said that there is no known method of replicating plastic deformation with the 550 nm absorption band by a laboratory treatment or growth process.
All fancy colored diamonds submitted to GIA’s grading laboratories are subjected to rigorous analysis to be certain that the colors ‒ and the diamonds themselves ‒ are of natural origin, which makes the GIA database extensively detailed and valuable for research, Shigley said. He added that the team selected a representative sample of 1,000 pink diamonds to examine even more thoroughly for the Gems & Gemology article.

How are Laboratory-Grown Pink Diamonds Created?
There are laboratory-grown pink diamonds in the market, but they are created by three different methods, said Eaton-Magaña.
“The first, and by far the most common, is through irradiating (exposing to radiation) a laboratory-grown diamond that was grown with nitrogen impurities, then subjecting it to moderate temperatures (600°C to 1000°C) afterwards,” she said. “The vast majority of pink and related colors are made using this method.”
This process creates a defect in the crystal lattice (caused by a missing carbon atom adjacent to a nitrogen atom within the lattice) called a nitrogen-vacancy center that is responsible for the color. Eaton-Magaña said a tiny percentage of natural pink diamonds have this nitrogen-vacancy center, which is identifiable by spectroscopic lines at 575 nm and 637 nm.
“These nitrogen-vacancy pinks comprise about one half of one percent of the natural pinks in the GIA database,” she said. They are type IIa diamonds (a rare type of diamond with an exceptionally pure chemical composition: almost all carbon, with negligible amounts of nitrogen or boron) with a very uniform pink color and no visible colored lamellae. These stones are sometimes termed Golconda pinks, but they don’t necessarily have a connection to the Indian mine that closed in the late 18th century.
Generally, she noted, natural nitrogen-vacancy pinks have pale colors, while the laboratory-grown and treated diamonds are more highly colored. Additional testing, such as at a gemological laboratory, is essential to determine the cause of color in such diamonds.
The second method cited by the researchers occurs only in chemical vapor deposition laboratory-grown diamonds (CVD), where a 520 nm spectral band is created during growth that results in an orangy-pink color. GIA has only seen a few of these stones, they say, and the color was not as vibrant as other pink lab-grown diamonds.
The third method, which is even more rare, Eaton-Magaña said, is achieved by adding high amounts of silicon to the CVD growth process which, when exposed to UV illumination, creates reversible color change between the stable pink color and a temporary blue color.

Size and Color Statistics: Are Pink Diamonds Rare?
Of the group of diamonds in this study 47% were unmodified (no other color observed) pink; 28% were purplish pink to pinkish purple; 17% were brownish pink to pinkish brown; 10% were brownish orangy-pink to orangy-pink; 3% were brown; 1% were purple-brown, purple-gray and purple; and 0.9% were red, brown-red or orange red. Of the unmodified pink diamonds, 54% were graded faint to light pink.
While brown diamonds are among the most common fancy colors in nature, the low percentage of them in this group suggests that most are sold into the market without grading reports. The brown color is accompanied by other hues, such as pink or yellow, or the brown stones are treated to produce other colors.
The vast majority of the group (83%), weighed less than one carat, with 56% of them being under one-half carat. The dominant shapes were round (24%), pear (20%), rectangle (16%) and cushion (13%).
The research ‒ the most extensive ever carried out on pink and associated colored diamonds ‒ found that 25% are type IIa, which is much higher than with colorless to near-colorless diamonds (where the percentage is < 5%), Breeding said.
The majority of type Ia pink diamonds (diamond containing clusters or aggregates of nitrogen atoms as impurities in the crystal lattice) almost exclusively come from two sources: Australia’s Argyle mine and Russia, which also happen to be the most prolific and consistent producers of such stones. Type IIa pink and other type Ia pink diamonds come from other sources – such as Tanzania, South Africa, and Brazil – but there is no reported regular production from any mine.
“It’s unusual that these types are from very specific locales, especially because they are so rarely found in other sources,” Breeding noted, adding that because Argyle is the dominant source for highly saturated (colored) pink, purplish-pink and red diamonds; the decline in the numbers of such stones will be substantial after the mine closes next year.
Research Aids Automated Detection of Treatment/Lab Growns
This pink diamond study enables GIA to better understand how these rare and beautiful diamonds formed and the properties that give them their color. The researchers found many new details at the atomic level by analyzing the absorption spectroscopy and photoluminescence data. These findings add to the understanding of these amazing stones – which can enable faster, more accurate identification.
The research from this study reinforces GIA’s development of an upgrade for the GIA iD100® gem testing device that adds a function to accurately screen pink and related color diamonds for treatments and synthetics. Source: GIA @topic:4