Title: Diamond Research Gives Clues to the Formation of the Continents Abstract: This rough type Ib diamond, from Zimmi in West Africa, near the Sierra Leone-Libera border, contains a sulphide inclusion with compositions that give clues to how the West African continent formed. Photo by Karen Smit/GIA.

This is a summary of the article "Sulfur Isotopes in Diamonds Reveal Differences in Continent Construction" by Karen V. Smit, Steven B. Shirey, Erik H. Hauri and Richard A. Stern published on April 26, 2019, in Science.
Diamonds, one of the most valuable gemstones, are also very valuable to geoscientists. Mineral inclusions in diamonds are the most direct samples we have from the inaccessible depths of Earth. Inclusions in diamonds have given geoscientists information about water in the earth’s interior, mineralogy of the deep earth and metallic phases in the deep earth. Also, because there is no direct way to determine a diamond’s age from the diamond itself, mineral inclusions trapped within diamonds provide the only way to date diamonds. So, although inclusions in diamonds are often considered to be undesirable in the gem trade, they are extremely valuable scientific samples.
In our study, we measured the sulphur and rhenium-osmium isotopes in sulphide inclusions in diamonds from the Zimmi region of Sierra Leone. The sulphides are tiny minerals, often between 100 and 300 microns across, trapped in the diamonds during growth.
We found that the sulphides recorded two episodes of subduction in the West African continent. Subduction is when the oceanic crust is thrust under another tectonic plate during collision into the deep earth. The first subduction event recorded by Zimmi sulphides occurred around three billion years ago and the second was around 650 million years ago.

Sulphide inclusions still trapped in the Zimmi diamonds. Sulphides are silver-grey in appearance and are surrounded by blackened fracture systems. These fractures develop during kimberlite ascent because the sulphides expand more than the diamond. Photo by Karen Smit/GIA
3 billion-year-old subduction
The sulphides have isotopic compositions that indicate the sulphur was cycled through the ancient atmosphere prior to the rise of oxygen 2.5 – 2.3 billion years ago (Farquhar et al., 2001). This is indicated by mass-independently fractionated (MIF) sulphur isotopes. Any modern sulphur (or sulphur that did not cycle through the ancient atmosphere) will not have these MIF isotopes1. The presence of MIF sulphur in these sulphide inclusions indicates that they have a surficial origin in the earth’s ancient atmosphere. The sulphides were likely emplaced into the deep earth around 3 billion years ago – a time that has been well established for subduction and incorporation of oceanic crust material into the mantle2,3.
650 million-year-old subduction
We also measured the rhenium-osmium isotopes in these sulphide inclusions. Rhenium-osmium is the most widely used technique to date the time of diamond formation4. Zimmi diamonds were found to have 650-million-year-old ages5, an age that overlaps with subduction and collisional mountain building in the region, between 700 and 550 million years ago. Subduction of oceanic crust and subsequent dehydration of the oceanic crust would have introduced carbon-bearing fluids into the deep earth for diamond formation6.
Why do we find this interesting?
Earth’s oldest continents (called cratons) are stabilized by lithospheric mantle keels. The stability of Earth’s continents in the face of destructive tectonic activity is an essential geologic backdrop for the emergence of life on our planet. Since this is the only tectonically active, rocky planet that we know, understanding the geology of how our continents formed is a crucial part of discerning what makes Earth habitable.
The stability of cratons depends on the underlying mantle keels that are around 150 – 200 km thick. The processes for how these mantle keels form are still debated, and there are several different theories for their origin. Some of the models for craton formation involve subduction-style plate tectonics where plates are subducted into the deep earth and stabilize the cratonic keels. Other models do not invoke subduction, and instead, require deeper mantle processes like melting in mantle plumes or melting at oceanic plateaus.
Luckily these mantle keels have the ideal conditions for diamond formation. The majority of natural diamonds form in these cratonic mantle keels. Diamonds become important samples that can be used to investigate how the stabilizing keels below the oldest continents are formed.
Sulfur isotopes in diamonds, combined with their Re-Os ages, can be used to track multiple subduction events during craton growth, even those separated by billions of years. Subduction processes were essential to the growth and modification of the West African craton over a period of 2 billion years.
We compared our results to diamonds from southern Africa and northern Canada. We found that this combined isotopic approach also reveals differences in craton construction worldwide. Similar to the Zimmi diamonds, diamonds from the Jwaneng and Orapa mines in southern Africa do contain MIF sulfur1,7. This indicates that subduction was also an important process in the construction of the cratonic mantle in southern Africa.
But diamonds mined in northern Canada do not show the same sulphur chemistry. Diamonds from the Ekati mine have 3.5-billion-year-old rhenium-osmium ages and do not have MIF sulphur8,9. This means that the mantle keel in this region originated in some way that did not incorporate surface material. The sulphur in the Canadian diamonds does not tell us how the mantle keel formed, only how it did not.
Our work shows that sulphide inclusions in diamonds are a powerful tool to investigate craton construction processes.

Sulphide inclusion that has been broken out of a diamond and imaged in a scanning electron microscope. This sulphide has cubo-octahedral morphology and trigons on its surface. Both these features were imposed on the sulphide by the diamond. Image by Karen Smit/GIA

How did we do this?
To characterize the diamonds and image the inclusions, we first laser cut and polished double-sided plates of the diamonds.
Rhenium-osmium isotopes
We broke the diamond plates using a small hammer and a steel cracker to release the sulphide inclusions. The inclusions are tiny and weighed between 3 and 162 micrograms. After breaking each inclusion out of the diamond, we imaged it and analyzed its major element composition using a scanning electron microscope.
In a clean laboratory, we then dissolved the sulphide in some acid along with a known amount of tracer solution known as an isotopic spike. Chemical procedures are done to separate rhenium and osmium into different acidic solutions. The solutions that contain rhenium and osmium are each dried down on a hotplate.
The dried-down salt of osmium is placed on a metallic filament, which is then placed in a thermal ionization mass spectrometer (TIMS). The filament is heated to produce ions that are then accelerated through the instrument and the different osmium isotopes are measured on a very sensitive detector.
The dried-down salt of rhenium was taken up into a dilute acid solution. That solution was introduced into a multi-collector inductively coupled mass spectrometer (MC-ICP-MS). The solution was ionized in a plasma and those ions were accelerated through the instrument, where the two different rhenium isotopes were measured simultaneously on very sensitive detectors.
The amount of rhenium and osmium that we measured in the sulphides is in the femtogram to picogram range - where 1 femtogram is 10-15 g or 1 part per quadrillion (ppq) and 1 picogram is 10-12 g or 1 part per trillion (ppt). Because we are measuring such tiny amounts, any small amount of contamination can ruin the sample. This is why it is essential to do this work in a clean laboratory with dedicated supplies for diamond inclusion work.
Rhenium-osmium analyses were done using chemistry labs and a Thermo-Fisher Triton instrument at the Department of Terrestrial Magnetism at the Carnegie Institution for Science.
Sulphur isotopes
Sulphide inclusions were not broken out of the diamonds for sulphur isotope measurements. Instead, we polished the diamond plates down further with a diamond scaife to expose the sulphide inclusions. It took a few hours to a day to expose each inclusion.
Diamond plates with the exposed sulphide inclusions were placed in a secondary ion mass spectrometer (SIMS). The samples were bombarded with a cesium ion beam to create small pits in the sulphides. The material released from the sulphides was then accelerated through the instrument and the four different sulphur isotopes were measured simultaneously on very sensitive detectors.
Sulphur isotope measurements were done using a Cameca IMS 1280 instrument at the University of Alberta. Preliminary measurements were done using a Cameca NanoSIMS at the Department of Terrestrial Magnetism at the Carnegie Institution for Science.
About the diamonds themselves
Diamonds for this study are from the Zimmi alluvial deposit in Sierra Leone. The Zimmi mining area is located south of the town Zimmi, near the Libera-Sierra Leone border. The Zimmi locality is known for producing yellow diamonds with abundant sulphide inclusions.
The Zimmi diamonds have nitrogen impurities in the rare isolated form that classifies them as Type Ib diamonds. Type Ib diamonds are exceptionally rare among natural diamonds and account for less than 0.1% of worldwide natural diamonds.
The Authors
Karen V. Smit has been a research scientist at the Gemological Institute of America (GIA) since 2014. She is interested in using diamonds and their mantle host rocks to understand diamond formation processes in the deep earth. Her research focuses on the origin of the earth’s continents, how plate tectonic processes influence diamond stability, and most recently in using the spectroscopic features of natural diamonds to distinguish them from lab-grown and treated diamonds.
Steven B. Shirey has been a staff member at the Department of Terrestrial Magnetism of the Carnegie Institution for Science for 34 years. Shirey's research focuses on the evolution of Earth's continents, especially as a function of mantle evolution. His interest in diamonds began more than 20 years ago as a way to examine continent formation and plate tectonics from the deepest possible perspective in the mantle.
Erik H. Hauri (now deceased) was a staff member at the Department of Terrestrial Magnetism of the Carnegie Institution for Science for 24 years. He passed away in 2018. Hauri was interested in the geochemical cycles of volatiles on the earth and moon and their relationship to planetary dynamics. Hauri's remarkable expertise in secondary ion mass spectrometry led to breakthroughs in understanding the water content of the moon, and the analysis of stable isotopes in diamonds and their mineral inclusions.
Richard A. Stern is a research scientist and ion probe facility manager at the University of Alberta. His research over the last 25 years has focused on developments and applications of secondary ion mass spectrometry to a broad range of topics in geochemistry and geochronology, most recently emphasizing light stable isotopes.

References
1. Farquhar et al., 2002
https://science.sciencemag.org/content/298/5602/2369

2. Barth et al., 2002
https://www.sciencedirect.com/science/article/pii/S0301926802001110

3. Aulbach et al., 2019
https://academic.oup.com/petrology/advance-article-abstract/doi/10.1093/petrology/egz011/5364029

4. Pearson et al., 1998
https://www.sciencedirect.com/science/article/pii/S0012821X98000922

5. Smit et al., 2016
https://www.sciencedirect.com/science/article/pii/S0301926816300882

6. Smit et al., 2019
https://www.sciencedirect.com/science/article/abs/pii/S0009254119301895

7. Thomassot et al., 2009
https://www.sciencedirect.com/science/article/pii/S0012821X09001447?via%3Dihub

8. Westerlund et al., 2006
https://link.springer.com/article/10.1007%2Fs00410-006-0101-8

9. Cartigny et al., 2009
https://www.sciencedirect.com/science/article/pii/S0024493709002497?via%3Dihub Source: GIA @topic:7


Title: Laboratory-Grown Diamonds: Demand Rises, Prices Fall Abstract: This 5.19 ct near-colorless type IIa CVD synthetic diamond is one of the largest faceted CVD synthetics seen at GIA. GIA photo

The proliferation of laboratory-grown diamonds into the market continues to dominate industry news.
A new report says demand for lab-grown diamonds has experienced “significant growth” from attractive marketing, but that prices for such goods have declined 70% in the past two years. The report, compiled by Bain & Co. and published by Rapaport, says the price decline is caused by improving technology that lowered production costs.
The consulting firm also noted that its consumer survey found that demand for lab-grown diamonds falls off sharply when their price tops $1,000 per carat.
Lab-grown producers, other than De Beers/Lightbox, claimed in the report that demand is running above supplies for their products, so prices are not dropping – especially for larger stones that remain difficult to produce.
The Bain view, however, is that prices will likely continue to decline to the point where the two markets “separate themselves,” similar to what happened with colored stones.
NATURAL DIAMONDS
The world’s two largest diamond miners – De Beers and Alrosa – continued cautious supply policies into the first third of the year. Both cut back on rough sales compared to last year, as their clients – diamond manufacturers – complain of softening prices and rising inventories, especially of small, lower quality goods.
The De Beers February/March cycle totaled $490 million, a 13% decline from the same period last year, but the firm held the line on prices after lowering them on some goods last fall. The trade generally welcomed the lower allocations, which include sight sales and individual deals, but claimed that softening polished prices have cut margins.
De Beers production also slid about 10% in 2018 – 32 million cts compared to 35 million cts in 2017 – although revenues increased 4% as the company shifted more of its sales toward higher quality goods.
De Beers noted: “The outlook for 2019 global diamond jewelry consumer demand faces a number of headwinds, including the risk of a potential intensification of U.S.-China trade tensions, the Chinese government’s ability to rebalance economic growth towards consumption, and further exchange rate volatility,”
Alrosa announced that its February rough sales were $340.6 million, up 23% over its January allocation. While the headline stated it was an increase, sales for the first two months of the year were more than 35% below the same period of 2017. The company did note improving demand from some Indian manufacturers, despite “some challenges hampering access to bank financing for the industry.”
KIMBERLEY PROCESS
The United Nations (U.N.) approved a resolution aimed at expanding the mandate of the Kimberley Process (K.P.) to exclude diamonds produced in a climate of “systemic violence” in addition to civil conflicts. This means that diamonds produced in areas where workers and local residents are killed, injured or abused by government, local militia or private security forces may be sanctioned if the measure is adopted. This is a major expansion that can allow, for the first time, diamonds from countries not engaged in civil wars to be excluded by the K.P.
Although the U.N. adopted the resolution and the World Diamond Council approved it, it’s hardly a done deal. The K.P. itself has to adopt the change, and, since that requires unanimous approval from every member country, nothing is guaranteed.
The U.S. tried to push this expansion a decade ago to no avail – it was met with fierce opposition from many African producer countries, particularly those bordering Zimbabwe, who feared reprisals from their larger neighbor. At that time, Zimbabwe’s government was under fire for major human rights abuses at the Marange mining area and assumed (not entirely wrongly) the change in the K.P. was directed at them.
After the U.N. approved the resolution, a coalition of non-governmental organizations (NGOs), The Civil Society Coalition, issued a call to ban diamonds from Zimbabwe based on the fact that the country’s army is involved the mining process. The army violently assumed control of the diamond deposits in 2006 after hundreds of artisanal miners had settled into the area to dig for stones. An estimated 180 people died in the conflict, while human rights abuses allegedly continued for years afterward.
An effort to expel Zimbabwe from the K.P. a decade ago was defeated on the grounds that Zimbabwe’s government was the recognized authority and that sanctions were only applied to rebel groups. Source: GIA @topic:8


Title: GIA Researchers Look Inside Black Diamonds Abstract: The contrast of black and white is a favorite in fashion, including jewelry. This ring, left, has 1.5 carats of black diamonds and 1.50 carats of colorless diamonds. The earrings have 1.69 carats of black diamonds and 1.76 carats of colorless diamonds. All three pieces are set in 18K gold. Courtesy of Nanci Knott & Co. Photo by Robert Weldon/GIA

The stark beauty of black diamonds has intrigued jewelry designers for decades, offering a striking contrast to their colorless counterparts in rings, necklaces and bracelets. Truly black diamonds, however, are not very common in nature and as a result, the majority in the market are treated to achieve a uniform black color.

An important source of black diamonds, both natural and treated, is the Marange deposit in eastern Zimbabwe. It is a relatively new and controversial diamond source yielding large quantities of diamonds with a combination of brown radiation stains and graphite inclusions that make them appear black or give them the ability to be treated to achieve that color. The source was discovered in 2001 by De Beers but not worked until 2006. A 2018 study by GIA researchers Karen V. Smit, Elina Myagkaya, Stephanie Persaud and Wuyi Wang reports in detail on the unique properties used to identify the color origin of Zimbabwe black diamonds and how to identify potential treatments.

Table-up images of the 40 natural Fancy Dark brown to Fancy black Marange diamonds from this study. The diamonds range between 0.39 and 3.11 ct, and between 4.47 and 8.75 mm in diameter (see table 1). All the diamonds have a dark appearance due to graphite needles and abundant radiation stains, except for four with dark clouds comprised of micron-sized inclusions of graphite. Photos by Jian Xin (Jae) Liao.
The GIA researchers analyzed a suite of 40 natural Fancy Dark brown to Fancy black diamonds, weighing 0.39 carats to 3.11 carats, for the study published in the Summer 2018 edition of Gems & Gemology, GIA’s quarterly professional journal.  All of the round cut diamonds were acquired from the trade polished and untreated. Photos show that the color is distributed unevenly in the majority of them, making them less suitable or unsuitable for jewelry.

The researchers subjected the diamonds to various tests, including several different spectroscopy methods to identify impurities and defects in the diamond crystal lattice. Inclusions (such as graphite) are normally distinguished from defects such as GR1, an irradiation-related defect that is also reviewed in the paper. DiamondView imaging was used to map the growth zoning.

DiamondView and visible light images of two diamonds that show radiation stains within fractures in the diamond. Non-luminescent regions in the DiamondView images are associated with extensive radiation damage along fractures in the diamonds. Photos and images by Karen Smit.
The black hue in many naturally colored diamonds is caused either by exposure to radiation or by inclusions of sulfides, graphite, magnetite, hematite or iron-bearing materials. Many treated black diamonds are so heavily irradiated that they look black, but instead are extremely dark green. The dark color in the Zimbabwe samples is caused by inclusions of graphite, methane or other dark minerals that are so prevalent within the stone that all or most of the diamond takes on that color. A number of them also contained brown colored radiation stains centered in the fractures.

The GIA researchers found that the majority of their Marange samples derived their dark colors from the abundant graphite needles and brown radiation stains in large fractures that reached the surface. The brown stains are likely the result of the diamonds residing at the Earth’s surface for at least 1 billion years and their exposure to radioactive fluids and minerals. While most diamonds exposed to radiation turn green, after heating to around 500-600°C these stains turn brown. While the fractured diamond probably would not survive the HPHT treatment process, they could withstand low pressure, high temperature treatment to turn them into gem-quality black diamonds.

The center of this ring features 1.13 carats of black diamonds and .56 carats of colorless diamonds. Courtesy of Four Seasons Jewelry Corporation. Photo by Valerie Power/GIA
Four of the samples had an unusual internal structure – they contained two different growth structures, octahedral and cuboid, which are called mixed-habit diamonds. The cuboid area of the diamonds had clusters of micron-sized graphite inclusions that appeared as a dark cloud. Another GIA study has shown that when heated above 1200°C, however, the graphite inclusions expand to 10 to 16 times their original size, that can create a uniform opaque black color. This makes Marange a potentially important source for treated fancy black diamonds.

The aim of the study was both to document the properties of black diamonds from Marange and to better understand how such unusual diamonds were formed. Because Marange produces a large amount of diamonds – several million carats yearly – these lower-quality graphite-containing diamonds represent a potentially major source for both treated and untreated black diamonds – especially because they tend to be larger than average run-of-mine diamonds, 5 to 7 carats.

Le Vian’s Sunflower Collection features black diamonds, which it calls Blackberry Diamonds®, and colorless diamonds, which it calls Vanilla Diamonds®. The ring, left, features .625 carats black diamonds and .375 carats colorless diamonds set in 14K gold. The earrings feature .25 carats black diamonds and .625 carats of colorless diamonds. Photos courtesy of Le Vian.
Lead author Karen V. Smit and a different team of researchers examined another group of mixed-habit diamonds from the same deposit to better understand diamond growth processes. The mixed-habit diamonds contained inclusions of ancient fluids of methane (carbon and four hydrogens). The study conducted by Smit, Steven B. Shirey, Richard A. Stern, Andrew Steele and Wuyi Wang appeared in the April 2016 issue of Lithos. Interestingly, these methane fluids were only located in the cuboid sectors of the diamonds, while the octahedral portions were free of them, due to the much faster growth rate of the cuboid sectors relative to the octahedral. These Marange diamonds are the first diamonds in which methane has been described, and has provided important constraints on how diamonds form in the deep Earth. Source: GIA @topic:7


Title: Nominal Type IaB Diamond with Detectable Uncompensated Boron Abstract: Figure 1. This 0.30 ct K-L diamond with faint brown color, mounted in an 18K gold prong setting, is a nominal type IaB diamond with detectable uncompensated boron. Photo by Wenqing Huang.

In recent years, nominal type IaAB and IIa diamonds with transient 2800 cm–1 FTIR absorption peaks arising from uncompensated boron produced under UV radiation have been reported (J. Li et al., “A diamond with a transient 2804 cm–1 absorption peak,” Journal of Gemmology, Vol. 35, 2016, pp. 248–252; Winter 2016 Lab Notes, pp. 412–413). The National Center of Supervision and Inspection on Quality of Gold and Silver Products recently examined a type IaB diamond that exhibited instantaneous 2803 cm–1 FTIR absorption shortly after exposure to an ultra-short-wave (< 230 nm) UV source.

Figure 2. DiamondView imaging shows blue fluorescence (left) and greenish blue phosphorescence (right) in the natural type IaB diamond. Images by Wenqing Huang.

Figure 3. The FTIR spectra reveal low concentrations of the hydrogen peak (3107 cm–1) and nitrogen impurities in the B aggregates (1174 cm–1) (blue line). Shortly after ultra-short-wave (< 230 nm) UV exposure, the transient boron-related absorption was recorded at 2803 cm–1 (red line). Spectra have been offset vertically for clarity.
Under ultra-short-wave UV excitation, the 0.30 ct K-L diamond with faint brown color, mounted in an 18K gold prong setting (figure 1), showed strong blue fluorescence and strong greenish blue phosphorescence that lasted for approximately eight seconds (figure 2). Infrared absorption spectroscopy showed low concentrations of the hydrogen-related peak (3107 cm–1) and nitrogen impurities in the B aggregates at 1174 cm–1 (figure 3), indicating a type IaB diamond (C.M. Breeding and J.E. Shigley, “The ‘type’ classification system of diamonds and its importance in gemology,” Summer 2009 G&G, pp. 96–111); prior to ultra-short-wave UV excitation, we were unable to detect the presence of the B center. No boron-related absorption was detected before UV radiation exposure, due to uncompensated B concentrations below the detection level of the FTIR spectrometer. But shortly after ultra-short-wave UV exposure, the transient boron-related absorption peak was recorded at 2803 cm–1 (again, see figure 3). Nitrogen-related peaks were detected at 415.7, 428.5, 439.0, and 452.4 nm using photoluminescence (PL) spectroscopy (figure 4); the peak at 415.7 nm belongs to the zero-phonon line (ZPL), while the others belong to its associated phonon replicas (A.M. Zaitsev, Optical Properties of Diamond: A Data Handbook, Springer-Verlag, Berlin, 2000). PL and FTIR spectra confirmed the diamond’s natural origin.

Figure 4. The photoluminescence spectrum of the sample excited at room temperature with a 405 nm laser reveals an N3 center with its zero-phonon line (ZPL) at 415.7 nm and its associated phonon replicas with peaks at 428.5, 439.0, and 452.4 nm.
The generally accepted mechanism for interpreting the phosphorescence in type IIb diamonds is donor-acceptor pair recombination processes involving boron and other defects (P.J. Dean, “Bound excitons and donor-acceptor pairs in natural and synthetic diamond,” Physical Review, Vol. 139, 1965, pp. A588–A602). Boron is deemed as the acceptor in the model, where the donor is believed to be nitrogen related, either as isolated nitrogen, aggregated nitrogen, or a plastic deformation–related defect (S. Eaton-Magaña and R. Lu, “Phosphorescence of type IIb diamonds,” Diamond and Related Materials, Vol. 20, 2011, pp. 983–989; E. Gaillou et al., “Boron in natural type IIb blue diamonds: Chemical and spectroscopic measurements,” American Mineralogist, Vol. 97, 2012, pp. 1–18). When almost all of the boron impurities received electrons from donors, almost no uncompensated boron (B0) was left behind, and therefore no boron-related absorption peaks were recorded. When the diamond was exposed to ultra-short-wave UV excitation, some of the compensated boron converted to an uncompensated state due to a charge transfer process between compensated boron and ionized donors, which could be recorded before the phosphorescence decayed. This mechanism is also suitable for interpreting the observed phenomenon of this specimen.
Natural diamonds with long-lasting phosphorescence under UV excitation are typically type IIb or chameleon diamonds (J.M. King et al., “Characterizing natural-color type IIb blue diamonds,” Winter 1998 G&G, pp. 246–268; T. Hainschwang et al., “A gemological study of a collection of chameleon diamonds,” Spring 2005 G&G, pp. 20–35). It is rare to find diamonds of other types, especially type IaB diamonds, showing this phenomenon. Finding a detectable, if temporary, B0 defect in a type IaB diamond is also unusual. Source: GIA @topic:4


Title: Pink Diamonds, Russia’s Amber Room, and More… Abstract: The beauty and desirability of pink diamonds is exemplified by the Winston Pink Legacy, a stunning 18.96 ct Fancy Vivid pink diamond that realized US$50 million at auction in November 2018. Such sought-after diamonds are the subject of the third installment of our colored diamonds series. GIA researchers Sally Eaton-Magaña, Troy Ardon, Karen Smit, Christopher Breeding, and James Shigley summarize the current science on natural-color pink to red diamonds and detail the cause of their color. The authors provide an unprecedented gemological and spectroscopic characterization by presenting absorption and luminescence spectra drawn from a representative sample of 1,000 diamonds from GIA’s database.

“An unprecedented characterization of naturally colored pink to red diamonds…”

Our second paper, by GIA’s Russell Shor, surveys the history of the legendary Amber Room. Originally commissioned for Prussia’s King Frederick I in the early 1700s and presented to Czar Peter I of Russia in 1716, the amber panels disappeared from St. Petersburg during the Second World War. In 1979, the Soviet Union initiated a painstaking reconstruction of this cultural treasure. Besides its rich history, the author provides firsthand accounts from those who participated in its recreation.
Next, Che Shen, a graduate student at the Gemmological Institute of China University of Geosciences in Wuhan, and Ren Lu investigate the color origin of gem-grade diaspore using LA-ICP-MS spectrometry.
A reaction rim or “corona” results from alteration of a crystal’s exterior after its formation due to changes in geological conditions. In our fourth paper, researchers led by Nguyen Ngoc Khoi, from the Hanoi University of Science, provide a study on corundum with spinel corona from northern Vietnam. The authors explain the genesis of the corona by examining its reaction textures, chemical composition, and mineral inclusions and applying thermodynamic phase equilibria calculations.
Our fifth paper offers a gemological characterization of pipi pearls from the bivalve mollusk Pinctada maculata. Authors Nanthaporn Nilpetploy, Kwanreun Lawanwong, and Promlikit Kessrapong detail the internal structures and further investigate these small, sometimes strongly colored natural pearls using microradiography and UV-Vis, Raman, and photoluminescence spectroscopy.
Our final article is a brief summary of diamond inclusions by GIA’s Nathan Renfro, John Koivula, Jonathan Muyal, Shane McClure, Kevin Schumacher, and James Shigley. A foldout wall chart with photomicrographs showcasing remarkable inclusions in natural, synthetic, and treated diamonds accompanies this article.
Besides our six articles and the chart, there’s plenty to enjoy in our regular features: Lab Notes offers analysis of three freshwater blister pearls attached to their host shells, De Beers’ Lightbox CVD-grown diamonds, and an exceptionally rare Montana ruby. Our new Diamonds from the Deep section provides an examination of how diamonds form in the deep earth. Micro-World serves up an array of internal features observed in gem materials, while Gem News International reports on sapphire treated with high pressure and high temperature, coated rough and faceted synthetic moissanite, and gemological conferences around the world.
Finally, don’t forget to check our listing of the 2018 G&G Challenge winners, and please do remember to cast your vote for the Most Valuable Article of 2018. Source: GIA @topic:4


Title: Mixed-Type Treated Red HPHT Synthetic Diamond Abstract: Figure 1. This 0.27 ct Fancy Dark red specimen is a multi-step treated HPHT synthetic diamond. Photo by Meili Wang.

A multiple-treatment process involving irradiation and HPHT annealing can produce pink to red color in natural and synthetic diamonds; specimens treated by this process have been on the market for over 10 years. To the best of our knowledge, nearly 95% of the studied red HPHT synthetic diamonds treated by the multi-treatment process are classified as type Ib or type IIa. Recently, we examined a treated red HPHT-grown synthetic diamond that was confirmed to be mixed type (IaA + IaB + Ib).

The 0.27 ct round brilliant sample, graded as Fancy Dark red (figure 1), had a metallic inclusion under the table. The DiamondView image showed strong red fluorescence and cuboctahedral growth structure; the latter is a typical feature of HPHT-grown diamonds (figure 2). Ni-related defects at 883.1/884.8 nm and 793.6 nm were revealed by a photoluminescence (PL) spectrum at liquid-nitrogen temperature with two different laser excitations (532 and 785 nm). The H2 defect corresponding to a sharp peak at 986.2 nm and the NV center associated with a strong peak at 637 nm were also found. In addition, the Fourier-transform infrared (FTIR) absorption spectrum (figure 3) confirmed the material was an uncommon type of IaA + IaB + Ib, with absorptions at 1282 cm–1 (A center), at 1175 cm–1 (B center), and at 1131 and 1344 cm–1 (C center), respectively (again, see figure 56). This mixed type is similar to that observed in treated natural diamonds. A moderate 1450 cm–1 absorption (H1a), which correlates with irradiation and subsequent annealing (Clark et al., “Absorption spectra of natural and irradiated diamonds,” Proceedings of the Royal Society of London A, Vol. 234, 1956, pp. 363–381), was also present. Thus, this diamond was identified as a multi-step treated HPHT synthetic diamond, with irradiation and HPHT annealing indicated as treatment processes.

Figure 2. The DiamondView fluorescence image shows cuboctahedral growth structure, a typical feature in HPHT-grown diamonds. Photo by Wen Han.

Figure 3. FTIR spectroscopy reveals that this diamond is type Ia + Ib, with the existence
of aggregated nitrogen atoms (A center at 1282 cm–1 and B center at 1175 cm–1) and
isolated nitrogen (C center at 1131 and 1344 cm–1) impurities. The H1a absorption
at 1450 cm–1, correlating with irradiation and subsequent annealing, is also observed.
Although most of the recent treated red HPHT synthetic diamonds are reported to be type Ib or type IIa (e.g, Fall 2016 Lab Notes, pp. 308–309; C.M. Breeding and J.E. Shigley, “The ‘type’ classification system of diamonds and its importance in gemology,” Summer 2009 G&G, pp, 96–111), such diamonds with mixed type Ia + Ib are available in the jewelry market, as exemplified by this study. Therefore, caution is still needed to distinguish such treated synthetic diamonds from treated stones of natural origin, as they may show similar characteristics. Source: GIA @topic:4


Title: Very Large Artificially Irradiated Yellow Diamond Abstract: Figure 1. This 59.88 ct Fancy Vivid yellow diamond was treated through artificial irradiation and annealing. Photo by Jian Xin (Jae) Liao.

Artificial irradiation and annealing to enhance or change color is one of the oldest diamond treatments. English chemist Sir William Crookes first discovered the effects of radiation on a diamond’s color, conducting experiments using radium salts in 1904. Today, only a very small percentage of all natural diamonds are irradiated, typically with an electron beam. Because of the risk of damage, diamonds subjected to this treatment are typically under 10 carats.

A 59.88 ct yellow diamond (figure 1) recently examined at the New York laboratory received clarity and color grades of SI1 and Fancy Vivid yellow. While the face-up color distribution was classified as even, we observed a moderate color concentration along the culet typical of some artificially irradiated diamonds (figure 2). Microscopic examination showed noticeable crystal inclusions at 10× magnification as well as extensive burn marks across the entire surface of the stone. The diamond showed chalky blue fluorescence under long-wave UV excitation and medium yellow fluorescence under short-wave UV.

Figure 2. Strong color concentration along the diamond’s culet is evidence of artificial irradiation. Photo by Christopher Vendrell.
Using a desktop spectroscope, the diamond’s visible absorption spectrum revealed a series of absorption lines between 415 and 477 nm, indicative of a “cape” diamond. Additionally, an unusually strong peak at 503.2 nm (H3) was noted using a UV-visible spectrometer (figure 3). The enhancement of this H3 center is responsible for the very desirable yellow color. The infrared absorption spectrum showed high concentrations of nitrogen in the one-phonon region, indicating type Ia diamond. Further examination of the infrared region revealed a minor hydrogen defect as well as weak to moderate peaks at approximately 4935 cm–1 (H1b) and 5165 cm–1 (H1c), further evidence of treatment.

Figure 3. The yellow diamond’s Vis-NIR absorption spectrum shows a strong peak
corresponding to the H3 defect observed at about 503 nm.
These features led to the conclusion that the diamond was artificially irradiated and annealed (by introducing the H3 defect) to induce a more desirable yellow color. This was by far one of the largest artificially irradiated diamonds identified at GIA, surpassing previous examples by several carats (see Summer 2012 Lab Notes, p. 132; Winter 2014 Lab Notes, p. 295). This diamond reiterates the importance of careful analysis, since even the largest stones may have undergone treatment. Source: GIA @topic:4


Title: Evidence of Focused Beam Irradiation in Treated Pink Diamond Abstract: Figure 1. This DiamondView image of the table of a pink diamond shows two distinct pink spots. Field of view approximately 5 mm. Image by Troy Ardon.

	A Fancy pink diamond, confirmed as natural-grown, was found to be type IIa and colored by
	NV– centers. As part of routine testing, DiamondView fluorescence images were collected to check for synthetic growth features. These images showed unusual patterning in the form of two pink spots near the edge of the table facet (figure 1). Both spots were approximately 0.9 × 0.7 mm, and the table facet was approximately 3.0 mm in diameter. The orange fluorescence throughout most of the table was likely due to NV0 centers, whereas the pink components were likely due to NV– centers.

	To further investigate the spatial distribution of the NV0/– centers, we acquired a photoluminescence (PL) image of the diamond’s table using a 532 nm laser. Figure 2 shows the distribution of the NV0 and NV– centers. The distribution of the NV centers confirms the presence of two spots on the table. Figure 3 shows the average PL spectra from inside one of the spots and the average PL spectra from the region outside the spots. Figures 2 and 3 demonstrate that the intensity of the NV centers was greater inside the spots than in the rest of the table. Inside the spots, the average peak area intensity of the NV0 center was approximately two times greater and the average peak area intensity of the NV– centers was approximately three times greater. The spots were comparable in both size and defect concentrations.

	Figure 2. Left: A PL map showing the peak area distribution of the NV0 center. Field of view is approximately 3 mm; scale is relative intensity. Right: A PL map showing the peak area distribution of the NV– center. Field of view is approximately 3 mm; scale is relative intensity.

	Figure 3. A comparison between average PL spectra from inside one of the spots and the area outside the spots. The y-axis scale is the same for both spectra, so it is apparent that the intensity inside the spot is higher for both NV0 and NV– centers.

	To determine the vertical distribution of the NV– center, a 500 µm PL depth profile was acquired through each spot. This is an automated process the instrument can perform in which a series of spectra are collected along a line spanning the diameter of the spot. The stage is then offset 5 µm in the vertical direction to focus farther into the diamond, and another series of spectra are collected. The process was repeated 100 times until the target depth of 500 µm was reached. This achieved a depth profile of NV– luminescence, indicating how deeply the irradiation beam had penetrated into the stone. One spot showed an average penetration depth of 100 µm and the other 50 µm. It is important to note that this is axial displacement, which in confocal microscopy is an approximation of the true depth of the illuminated feature. Nevertheless, this demonstrated the shallow penetration of the irradiation beam.

	The intensity variation in the NV centers strongly demonstrated that this diamond was HPHT annealed and isolated nitrogen was subsequently introduced due to disaggregation of the A-form nitrogen (pairs of nitrogen atoms) or B-form nitrogen (four nitrogen atoms around a vacancy). It also indicated that this diamond was irradiated by a focused electron beam with relatively low energy (≤1 MeV) prior to annealing. These multiple processes introduced high concentrations of NV centers into the localized shallow areas. Furthermore, an increase of electron donor defects at the incident beam area would lead to the observed patterned distribution of the NV– centers. The narrow, focused nature of the electron beam is responsible for the distribution of the defects into the two spots and therefore the reason why the pink spots are observed in the DiamondView image. The two spots may be the result of two separate beams in the irradiation setup. Alternatively, the second spot may be from an additional round of treatment designed to further enhance the color. It is also unusual for the treatment to be done through the table rather than on the culet. It is unknown what benefits the focused beam will have over wide-beam irradiation. Source: GIA @topic:4


Title: Screening of HPHT Synthetic Melee With Natural Diamonds Abstract: Figure 1. This parcel of 3,005 melee diamonds with a total weight of 70.56 carats was submitted for analysis. Photo by Ivana Petriska Balov.

Significant amounts of melee-size synthetic diamonds produced by both HPHT and CVD technologies are manufactured for the jewelry industry. The “salting” of natural diamond melee parcels with HPHT-grown synthetic melee is seen more frequently in the trade today. This presents a threat to the integrity of diamond dealers and manufacturers who might unknowingly sell or use synthetic diamonds and represent them as natural. In response, GIA has introduced a melee analysis and screening service aimed at helping the trade combat this problem. The screening is rapid and relatively inexpensive. This service can screen large quantities of diamond melee and separate natural diamond from synthetic material (both HPHT and CVD grown), natural HPHT-processed diamond, and diamond simulants such as cubic zirconia or moissanite. In addition, a color grade within the D–Z range can be assigned to each diamond.

In August 2016, a group of 3,005 melee with a total weight of 70.56 carats (figure 1) was submitted to GIA’s New York lab for screening service. Initial testing using our fully automatic screening device, which is based on spectroscopic methods, passed 2,969 (98.7%) of them as natural diamond. Of the remaining 36, 12 were subsequently identified as natural material by methods including photoluminescence (PL) spectroscopy, and only 24 were referred for further testing to confirm their identity as natural, treated, or synthetic diamond.

Additional testing with Fourier-transform infrared (FTIR) absorption spectroscopy, Raman PL spectroscopy, and fluorescence imaging techniques identified 21 of these 24 melee as natural diamond. This analysis also confirmed that three (0.1%) of the melee in the parcel were HPHT-grown synthetic diamonds (figure 2).

Figure 2. From an initial screening of 3,005 melee diamonds, 24 specimens were
referred for further testing. Of these, three were HPHT-grown synthetic diamonds. Photo
by Jian Xin “Jae” Liao.
This highlights the practice of “salting” parcels of natural diamond melee with a small percentage of synthetic diamond melee, and the importance of advanced testing to identify them. Source: GIA @topic:4


Title: Synthetic Moissanite Imitations of Synthetic Colored Diamonds Abstract: Figure 1. Submitted as synthetic diamonds, the 0.99 ct blue-green emerald step cut (left), 0.85 ct brown-yellow standard round brilliant (center), and 1.90 ct deep green standard round brilliant (right) were all identified as synthetic moissanite. Photo by Yanjun Song.

Three faceted specimens were recently submitted to the Earth Science and Resources College of Chang’an University by a client who acquired them as synthetic colored diamonds (figure 1). All three specimens were relatively clean to the unaided eye. The RI of the specimens was over the limit of the gem refractometer. The average hydrostatic SG value was 3.21, and all samples were inert under long-wave and short-wave UV radiation. Microscopic examination revealed clear doubling of numerous stringers and some needle-like inclusions (figure 2). All of these features were consistent with synthetic moissanite (K. Nassau et al., “Synthetic moissanite: A new diamond substitute,” Winter 1997 G&G, pp. 260–275). Raman spectra of the samples were obtained using 785 nm laser excitation from three different orientations: parallel to the c-axis, perpendicular to the c-axis, and random orientation (one specimen’s spectra is shown in figure 3). Results for all three samples indicated synthetic moissanite, with the peaks at 149, 767, 789, and 967 cm–1 obtained from the random orientation (see rruff.info).

Figure 2. Needle-like inclusions (left) and doubling of numerous stringers (right) are shown here in the emerald step cut. Photomicrographs by Yanjun Song; field of view 4.22 mm (left) and 2.26 mm (right).

Figure 3. Raman analysis of the emerald step cut from three different optical orientations,
using a near-infrared wavelength of 785 nm, confirmed its identity as synthetic moissanite.
Moissanite (silicon carbide, or SiC) has many polytype structures, including cubic (C), hexagonal (H), and rhombohedral (R). Hexagonal structure 4H-SiC and 6H-SiC (space group P63mc) are the most common polytypes used as gem material. In this study, the characteristic peaks at 149, 767, 789, and 966 cm–1, obtained from the orientation parallel to the c-axis, were consistent with those previously reported for 6H-SiC (S. Nakashima and H. Harima, “Raman investigation of SiC polytypes,” Physica Status Solidi A, Vol. 162, No. 1, 1997, pp. 39–64).

High-quality colorless and black synthetic moissanites are common diamond imitations in the jewelry trade. As the growth techniques of synthetic moissanite continue to improve and the popularity of fancy-color diamonds increases in the Chinese market, we anticipate that high-quality synthetic colored moissanite will become more prevalent. Source: GIA @topic:4


Title: Yellow Synthetic Diamond with Nickel-Related Green Fluorescence Abstract: Figure 1. Under darkfield illumination, the pinpoint flux cloud is seen throughout the diamond. Photo by Lisa Kennedy; field of view 3.57 mm.

Gem-quality yellow synthetic diamonds have been a part of the industry for some time now. The gemological properties used to identify these synthetics have been extensively documented (see J.E. Shigley et al., “A chart for the separation of natural and synthetic diamonds,” Winter 1995 G&G, pp. 256–264).

GIA’s New York laboratory recently tested a 0.99 ct synthetic diamond with Fancy Vivid yellow color, disclosed as a product of HPHT (high-pressure, high-temperature) growth, which showed some unusual gemological features. Its UV-Vis absorption spectra showed a smooth rise from 500 nm to higher energy. The mid-IR absorption spectra indicated a type I diamond with isolated nitrogen (C-center) responsible for the intense yellow color. The sample displayed a moderate greenish yellow fluorescence under long-wave UV and slightly stronger greenish yellow fluorescence under short-wave UV. It had a noticeable pinpoint flux cloud throughout (figure 1) and obvious yellow color zoning following the growth sectors—both characteristic gemological features of a yellow HPHT-grown synthetic diamond.

Unlike other yellow HPHT-grown synthetics, the DiamondView images showed an unusual green fluorescent crosshatched pattern within the hourglass structure (figure 2). This closely resembles the pattern seen in natural diamonds, which means the synthetic could have easily been mistaken for a natural diamond. Under cross-polarized light, it showed a mottled strain pattern with moderate birefringence colors (figure 3). Most yellow HPHT-grown synthetics do not show a clear strain pattern and have weak birefringence colors. Further examination with PL spectroscopy using blue (457 nm) laser excitation showed that the green fluorescence was caused by the S3 defect (496.7 nm, shown in figure 4), which is due to the presence of nickel—a very unusual feature for an HPHT-grown synthetic diamond.

Figure 2. This DiamondView image shows the unusual green crosshatched pattern in
the hourglass structure of the HPHT-grown synthetic. Image by Lisa Kennedy.

Figure 3. Under cross-polarized light, the HPHT synthetic exhibited a mottled strain pattern with moderate birefringence colors. Photo by Lisa Kennedy; field of view 4.79 mm.

Figure 4. PL spectroscopy with blue (457 nm) laser excitation shows the S3 emission
band (496.7 nm), which is responsible for the HPHT synthetic diamond’s green
fluorescence.
This yellow HPHT-grown sample with gemological features we had not seen before shows once again how synthetic diamonds can be mistaken for natural diamonds. Caution must be taken, and careful gemological and spectroscopic analysis is essential. Source: GIA @topic:4


Title: Very Large Type Ib Natural Diamond Abstract: Figure 1. The yellow color of this gem-quality 13.09 ct type Ib natural diamond rough is due to the presence of isolated nitrogen (C centers). Photo by Jian Xin (Jae) Liao.

Nitrogen is the main impurity in diamond and during growth it is initially incorporated in the diamond lattice as isolated nitrogen atoms (C centers). Diamonds where the majority of nitrogen occurs in C centers are known as type Ib. While C centers are common in lab-grown HPHT diamonds, the occurrence of C centers in natural cratonic diamonds is extremely rare (<1% of all natural diamonds). Natural diamonds form deep in Earth’s mantle, where high temperatures result in nitrogen aggregating to form A centers (NS) and B centers (N4V).

GIA’s New York laboratory recently tested a large 13.09 ct gem-quality natural type Ib rough diamond. The diamond measured 13.51 × 11.56 × 10.18 mm, with rounded dodecahedral morphology and clear dissolution pits on some faces in a symmetrical pattern (figure 1). The diamond had a highly saturated, slightly orangy yellow color evenly distributed throughout the whole crystal. The diamond contained two tiny sulfide inclusions with their associated graphitic rosette fracture systems.

The infrared absorption spectrum revealed typical features of natural type Ib diamonds: a sharp peak at 1344 cm–1 and a broad band at 1130 cm–1. The absorption attributed to the A center (1280 cm–1) was rather weak. Spectral fitting showed that 75% of the nitrogen existed as C centers and 8% as A centers. This diamond did not contain any amber centers, which is consistent with the lack of plastic deformation lines or brownish hue.

The UV-Vis-NIR absorption spectrum, collected at liquid nitrogen temperature, showed a smooth and gradual increase in absorption from the near-infrared region to about 560 nm, and then a sharp increase to the high-energy side. C centers were the only color-introducing defect in this large diamond.

Photoluminescence (PL) spectra were collected at liquid nitrogen temperature with various laser excitations. Under 514 nm laser excitation, [N-V]0 at 574.9 nm and [N-V]– at 637.0 nm were detected. Many sharp emissions with unknown assignments were also observed (figure 2). With 830 nm laser excitation, weak emissions at 882/884 nm from Ni-related defects were observed.

Figure 2. The diamond’s PL spectrum, collected at liquid nitrogen temperature with 514 nm
laser excitation, showed emissions related to N-V centers along with many sharp peaks
of unknown assignment.
Large type Ib diamonds with intense yellow color are rarely seen. GIA continues to study these rare diamonds to understand the geological processes that allow isolated nitrogen to be preserved in some natural diamonds. Preservation of C centers in these natural diamonds is typically attributed to very young formation ages or to storage of these diamonds at cooler temperatures in Earth’s mantle than most other diamonds. Ongoing isotopic age dating of sulfide inclusions, combined with temperature constraints, will provide the opportunity to evaluate how these enigmatic type Ib diamonds are preserved in natural cratonic settings. Source: GIA @topic:4


Title: Polished Freeform Topaz Imitating Diamond Rough Abstract: Figure 1. The 13.70 ct topaz under daylight-equivalent light. Note the triangular features on each of the octahedral faces. Photo by Jian Xin (Jae) Liao.

Topaz is one of many near-colorless diamond simulant materials that may be faceted to bear a closer resemblance to diamond. Although most diamond simulants in the marketplace are faceted, every now and then, one comes across what appears to be a near-colorless octahedron diamond rough (see Lab Notes: Fall 1996, p. 205; Fall 1997, pp. 217–218; Fall 2007, p. 250; Fall 2009, pp. 230–231). A near-colorless 13.70 ct stone (figure 1) was recently submitted to the New York laboratory as a rough diamond from an alluvial source. At first glance, even with a well-trained eye, this stone could easily be misidentified. It bore a striking resemblance to diamond rough, with a “well-formed” octahedral shape and trigon-like formations on the surface of each of the faces. To further complicate the identification of this stone, topaz and diamond have the same heft due to overlapping specific gravities: 3.52 (+/-0.10) for diamond, 3.53 (+/-0.04) for topaz. The material was doubly refractive, with a spot RI reading of 1.61, properties consistent with topaz. Final confirmation came from Fourier-transform infrared (FTIR) spectroscopy, which revealed the distinctive topaz absorption spectrum shown in figure 2, with peaks at 4802 and 3650 cm–1 (K. Shinoda and N. Aikawa, “IR active orientation of OH bending mode in topaz,” Physics and Chemistry of Minerals, Vol. 24, No. 8, 1997, pp. 551–554).

Figure 2. Many absorption peaks related to the hydroxide ion in the crystal structure of
topaz are detected in this infrared absorption spectrum, including those at 4802 and
3650 cm–1. These have never been documented in any diamond absorption spectrum.
Although topaz can be easily shaped and polished into an octahedral shape, the trigon-like figures observed on the surface require an additional fabrication step and are not typically seen in octahedral-shaped simulants. Intentional material processing steps to mask a stone’s identity remind gemologists of the caution and care that need to be taken when dealing with gemstone identification—even when the identity of the material initially seems obvious. Source: GIA @topic:4


Title: CVD Synthetic Diamond with Unstable Color Centers Abstract: Figure 1. Left: These growth planes were observed in a CVD synthetic diamond; fine pinpoints were found along the growth planes. Photomicrograph by Meenakshi Chauhan; magnified 30×. Right: Pinpoints along the growth plane were also visible from the table. Photomicrograph by Meenakshi Chauhan; magnified 10×.

The Indian Gemological Institute – Gem Testing Laboratory, New Delhi recently examined a 1.42 ct (7.06–7.08 × 4.49 mm) round brilliant. Viewed perpendicular to the pavilion facets with its table down, the sample displayed a grayish yellow color, but a slight rotation changed the color to pinkish. On viewing the specimen parallel to the direction of the growth planes, the sample appeared grayish yellow; viewing perpendicular to these same planes, the sample appeared pinkish.

Infrared spectroscopy showed features typical for type IIa diamond. Magnification revealed no internal features except for a feather on the girdle and the two growth planes, which appeared textured. There are very fine pinpoint-like inclusions lying just along the planes (figure 1, left). These planes of pinpoints were also visible from the table (figure 1, right). Examined in the DiamondView (using less than 225 nm short-wave UV radiation) to reveal its growth patterns, the round brilliant showed parallel striations indicative of CVD growth (figure 2). It also exhibited moderate phosphorescence under the UV lamp for approximately 20–25 seconds. (figure 2, inset), confirming synthesis by a CVD process.

Figure 2. In the DiamondView, the 1.42 ct round showed striations typical of CVD growth. Notice the two parallel planes fluorescing stronger than the bulk of the crystal. The sample also showed moderate phosphorescence (inset), another indication of CVD growth. Images by Meenakshi Chauhan.
Upon removal from the DiamondView after approximately two minutes of exposure time, it showed a distinct grayish blue color. After exposure to a 100-watt halogen bulb for about three minutes, the synthetic diamond regained its initial color (figure 3).

Figure 3. The CVD synthetic diamond before (left) and after exposure (right) to the
short-wave UV radiation of the DiamondView. Photos by Meenakshi Chauhan.
This process was repeated, and the sample turned a grayish blue color after a single minute of exposure to the short-wave UV radiation of the DiamondView and regained its initial color in approximately one minute under the halogen light.

UV exposure produced unstable color centers in this CVD synthetic diamond, which gave it a grayish blue color. Heat removed the color centers, restoring the CVD synthetic diamond to its initial grayish yellow color. Source: GIA @topic:4


Title: Analysis of Melee Diamonds Using FTIR Spectroscopy Abstract: Figure 1. This 0.00054 ct colorless round brilliant was submitted for identification as a natural or synthetic diamond. Despite the specimen’s small size, an FTIR microscope can focus a beam through the facets to capture a high-quality infrared spectrum. Photo by Jian Xin (Jae) Liao.

The jewelry industry has expressed increasing concern over the possibility of treated or synthetic diamonds being mixed in with natural melee goods (those weighing less than 0.20 ct). Recently, GIA’s laboratory has seen a surge in notably small faceted melee diamonds submitted for identification. In melee sizes less than 0.01 ct, a standard Fourier-transform infrared (FTIR) spectrometer provides a less stable environment for analysis and produces an indistinct spectrum. Diamonds smaller than 0.01 ct prove challenging for other screening devices as well. Meanwhile, there is heightened pressure to identify both loose and mounted melee diamonds in the laboratory quickly and reliably so that each stone can be analyzed. In late 2014, GIA developed a new protocol to use an FTIR microscope to focus on melee diamonds as small as 0.00054 ct (figure 1) to produce high-quality spectra suitable for diamond typing.

Operating the FTIR microscope in reflection mode allows for fine-tuned aligning of the beam within a sample, improving the detail of the infrared spectra. Once a faceted round brilliant melee is stationed on a slide, the microscope beam can be focused either through the pavilion (if the melee is table-down) or through the table at an angle to reflect off an inner pavilion facet (if the melee is resting on the pavilion). Many of the samples were so small that the position of the stone remained unknown until the microscope was focused. Nevertheless, spectral quality was independent of stone position.

All 70 melee examined were natural round brilliants, the smallest a 0.00054 ct colorless sample identified as a type Ia diamond (figure 2). A few screening devices for treatment and synthetics have been introduced for diamonds over 0.01 ct. The FTIR microscope has proved very effective in analyzing melee smaller than this size, either loose or mounted.

Figure 2. This infrared spectrum of the 0.00054 ct diamond in figure 4, obtained using an FTIR microscope, shows the detail that can be captured from very small melee sizes.
The knowledge that GIA can type such small stones and determine their origin, either loose or mounted, apart from being an impressive test of FTIR microscopy, will increase consumer confidence in these remarkable melee diamonds. Source: GIA @topic:4


Title: Screening of Small Yellow Diamond Melee for Treatment and Synthetics Abstract: Figure 1. This group of 359 intensely colored round yellow diamonds (0.02–0.03 ct) was screened by GIA’s New York laboratory. Among these, the majority were natural (left), 14 were HPHT synthetics (middle), and one was HPHT-treated natural diamond (right). They all displayed uniform appearance and could not be distinguished visually. Photo by Sood Oil (Judy) Chia.

Diamond treatment and synthesis have undergone significant developments in the last decade. During this time, the trade has grown increasingly concerned about the mixing of treated and/or synthetic diamonds with natural melee-sized goods. Because it is often not feasible to test every small diamond in a parcel, many of these products could be traded without being tested individually by a gem lab. GIA’s New York laboratory recently tested two large groups of melee yellow diamonds submitted for screening of treatments and synthetics. The results will likely have profound implications for how melee diamonds are handled in the trade.

A parcel of 359 round diamonds between 0.02 and 0.03 ct was submitted for identification. They showed uniform appearance, intense yellow color, and good clarity. Based on spectroscopic analysis, each sample’s color was attributed to trace concentrations of isolated nitrogen. Gemological observations, infrared absorption spectroscopy, and DiamondView analysis confirmed that 344 of them were natural diamonds, 14 were grown by HPHT (high-pressure, high-temperature) synthesis, and one was an HPHT-treated natural diamond (figure 1).

Of the 14 synthetic diamonds, eight were dominated by A-aggregate form nitrogen with trace isolated nitrogen, while the other six showed negligible amounts. All had widespread pinpoint inclusions, a feature typical of HPHT synthetic diamonds. Characteristic growth features of HPHT synthesis were confirmed using a DiamondView fluorescence instrument on six of them. The synthetic diamonds with a high concentration of A-aggregate form nitrogen were produced at much higher temperatures, indicating more than one producer.

To gain perspective on the surprisingly high prevalence of synthetic and treated diamonds found in this parcel, we analyzed an additional parcel containing 525 samples, with similar results. One of these was HPHT-processed, while 10 displayed the spectral, microscopic, and fluorescence characteristics typical of HPHT synthetics; we concluded that the remaining 514 were natural and untreated. Typical DiamondView characteristics of HPHT synthetics were observed, but most of the HPHT synthetics showed fluorescence patterns similar to those of natural diamonds (figure 2). This observation emphasizes the importance of infrared absorption spectroscopy, in addition to DiamondView imaging, when determining diamond origin.

Figure 2. These DiamondView fluorescence images show (A) growth sector patterns typical of HPHT synthetic diamonds, (B) HPHT treatment, and (C and D) uncharacteristic HPHT synthetic patterns. Images by Martha Altobelli and Caitlin Dieck.
This study indicates that melee diamonds in the marketplace are being contaminated by synthetic and treated diamonds. Screening analysis by gem labs is essential to ensuring the correct identification. An efficient and reliable screening can be performed using infrared absorption spectroscopy, DiamondView fluorescence imagery, and optical microscopy. From our analysis of 883 melee samples in all, we concluded that 857 were natural diamond (97.1%), 24 were HPHT synthetic diamond (2.7%), and two were HPHT-processed natural diamonds (0.2%). Source: GIA @topic:4


Title: A Larger, Higher-Quality NPD Synthetic Diamond Abstract: In February 2014, these authors reported the first example of a synthetic nano-polycrystalline diamond (NPD) detected by a gemological laboratory. The 0.9 ct marquise was small and so heavily included with graphite crystals as to receive a Fancy Black color grade. The East Coast laboratory recently detected another undisclosed NPD synthetic diamond, a 1.51 ct Fancy Black round.

This NPD specimen was larger and had a much better transparency than the previous NPD, though it still graded as Fancy Black (figure 1). Infrared spectroscopy showed a diagnostic absorption pattern for diamond, with strong absorption in the one-phonon region (approximately 400–1332 cm–1). Absorption in this region is usually attributed to nitrogen impurity in different aggregation states, but careful observation showed otherwise.

Figure 1. This 1.51 ct Fancy Black nano-polycrystalline diamond (NPD) synthetic, submitted undisclosed, was larger and showed much better transparency than a previously detected NPD synthetic. Photo by Jian Xin (Jae) Liao.
The specimen’s infrared absorption pattern matched that of known NPD samples (figure 2). Further testing, including Raman spectroscopy and DiamondView imaging, confirmed the sample to be a NPD synthetic diamond. Microscopic observation revealed that the host material had the yellow color typical of previously reported NPD samples (see E.A. Skalwold, “Nano-polycrystalline diamond sphere: A gemologist’s perspective,” Summer 2012 G&G, pp. 128–131). The sample was heavily included with graphite, but less so than the previously reported 0.9 ct marquise, and therefore it had a better transparency (figure 3).

Figure 2. The mid-FTIR spectrum of the 1.51 ct black NPD synthetic diamond (red) displayed absorption in the one-phonon region similar to that of known NPD samples (green).

Figure 3. These photomicrographs, magnified 35× (left) and 40× (right), show abundant inclusions of graphite inclusions. Note the yellow color of the host material. Photomicrographs by Paul Johnson.
The origin of this synthetic diamond is not known, but it showed obvious improvements in size and quality compared to the marquise reported in February 2014. In the future, NPD synthetics could pose an identification challenge to the gem and jewelry industry. Careful gemological observations and advanced testing techniques were required to identify this undisclosed synthetic diamond. Source: GIA @topic:4


Title: Survey Shows: Diamond Sales Increased Last Year Abstract: Retail diamond jewelry sales topped $77 billion worldwide, according to a recent survey. The U.S. accounted for about half of that total. Above, a sales associate at Finell's Jewelers in Carlsbad, California shows a diamond ring to a customer. Photo by Valerie Power/GIA

Retail sales of diamond jewelry worldwide totaled an estimated US $77.5 billion in 2017, up from $74.6 billion in 2016, according to a survey by Tacy/Pharos Beam Consulting. This was the first sales increase in two years, according to the survey.

On the mining side, Tacy reports that the total mine production cost of rough diamonds was $7.5 billion last year, which nearly doubled to $14.72 billion in mine sales to the industry. De Beers sold $5.27 billion; Alrosa sold $4.17 billion; and other sales totaled $5.28 billion.

Diamond manufacturers’ polished output totaled $20.15 billion at wholesale prices, but sold $19.7 million into the market, leading to a supply overhang. Tacy estimates that some $300 million in recycled diamonds re-entered the market last year. Some sources peg that total at more than $1 billion, however.

De Beers’ Diamond Insight estimate of world diamond retail sales last year is $82 billion, with the U.S. accounting for $42.5 billion. Tacy puts U.S. sales at $37.3 billion. Tacy combines China with Hong Kong/Macau and Taiwan ($11.89 billion) while De Beers lists China mainland sales only ($9.85 billion.)

De Beers’ rough sales at its July cycle were lower than expected, about 8% below the July 2017 allocation and well below June’s totals. The $530 million sales total “reflected the seasonally quieter summer sales period for the midstream (diamond manufacturing) sector,” said CEO Bruce Cleaver.
DE BEERS MINES
De Beers is closing or selling mines at a much greater rate than it is commissioning new ones. Three years ago, it sold off nearly all of its South African operations and last year closed the Snap Lake Mine in Canada. It will also close the Victor mine in Canada and possibly shut its Namibian land operations next year.

De Beers will have only one operating diamond mine in South Africa by the end of this year: the Venetia operation, which is undergoing a $1.5 billion conversion to an underground mine. The company decided to close the Voorspoed mine in December, after 10 years of operation, because of high operating costs. Continuing production would have involved an expensive enlargement of the open pit and the grade was far below average, with revenues averaging less than $50 per ton, which is only about 20% the grade of its most profitable operations. The mine produces about 800,000 carats yearly and is a partnership between De Beers and the South Africa Black-Empowerment enterprise, Ponahalo Holdings.

The company’s only new mine this decade is the Gahcho Kue mine in Northern Canada, which it commissioned early last year. Source: GIA @topic:8


Title: Robust Demand Brings Increased Rough Diamond Sales Abstract: An array of rough diamonds, averaging about 0.4 ct each, from the Letseng Mine, Lesotho. Photo Russell Shor/GIA

Demand for diamonds and jewelry has been good around the world this year, and De Beers and Alrosa are betting it will carry through to 2019. Both companies have increased their sales volumes of rough diamonds significantly this year, based on this assumption.

De Beers announced it sold $575 million at its June 18-21 cycle (sight) and other allocations, a 6% increase over the same period last year. De Beers rough sales for the first six months of the year are even with or slightly behind last year’s total because of caution in the early months. The company often restates its monthly sales totals upwards, however, to account for deals made after the announcements, which usually come in the final week.

Alrosa, the Russian diamond agency, sold $390.3 million worth of rough in June, an 8% increase over sales for the same month last year. The company’s rough sales for the first half of the year are also up 8%. Alrosa markets nearly all diamonds produced in its home country and the Catoca deposit in Angola. The higher totals came from increased sales volumes and not as a result of price hikes.

“Sentiment in the diamond industry’s midstream is positive following the JCK Las Vegas trade show at the start of the month, and we continued to see good demand for our rough diamonds across the product range,” said De Beers CEO Bruce Cleaver in announcing the cycle totals.
PRODUCTION
Boutique diamond producers continue to find very large diamonds.

Lucapa discovered a 114 carat (ct) diamond at its Lulo Mine in Angola on July 11 and an 89 ct yellow at its Mothae Mine in Botswana last month. Canada’s new Gahcho Kue mine produced its largest diamond thus far, a 95 ct colorless crystal.

Lucara Mining, which found the 1,109 ct Lesedi La Rona diamond at its Kerowe mine in Botswana several years ago, is again concentrating its extraction activities in the portion of the kimberlite that produced the Lesedi La Rona and several other very large crystals. A recent bulk sample from the section found 47 diamonds weighing more than 10.8 carats, including a 100 ct-plus and six larger than 50 carats.

The Kimberley Process reported that world diamond production in 2017 increased 19% to 150.9 million carats, due in large part to two new mines in Canada, Gahcho Kue and Renard. Canada is the world’s second largest diamond producer with 23.2 million carats valued at $2.06 billion, behind Russia, which mined 42.6 million carats valued at $4.1 billion.
RETAIL
The recent Supreme Court decision allowing U.S. states to collect sales taxes for online sales is a victory some 30 years in the making for Jewelers of America (JA), a trade organization representing companies from all areas of the jewelry supply chain. Ever since U.S. catalog companies began to sell jewelry and not charge sales tax except to customers living in the companies’ home state, JA has argued that it gives remote sellers an unfair advantage. The situation grew much more acute with the rise of online sales.

The savings on a high value piece of jewelry can be considerable. Some 45 of the 50 states collect sales taxes, the highest topping 9%, with some local jurisdictions (New York City and Las Vegas, for example) tacking their own levies onto the state rates.

Exactly how much or how little brick and mortar retailers will win from the decision remains to be seen. As usual, the devil is in the details because every state has a different rate, different rules (some items are exempt from taxation, for example) and different processes for filing. Also, since many brick and mortar jewelers now have online businesses, this court decision could become a doubled-edged sword.

The court ruling, of course, does not bring immediate change because each state must enact its own online tax collection rules. And some states already charge sales tax for online transactions. For example, Blue Nile collects sales tax from customers in Hawaii, Maine, Mississippi, New York, Oklahoma, Virginia and Washington state because it has physical presences (nexus) in these states, and Amazon collects sales taxes from every state that has a sales tax. Source: GIA @topic:8


Title: 2018: A Good Year for Finding Mega-Diamonds Abstract: The 472 ct diamond from Lucara Diamond’s Kerowe mine is the largest found at the mine this year, which has, thus far, yielded five diamonds over 100 carats. Photo courtesy of Lucara Diamond Corp.

It’s turning out to be a good year for very large diamonds.

The three diamond mining companies that specialize in digging up large stones have found some really big ones during the first quarter of the year, ending a relative drought.

Gem Diamonds unearthed five diamonds over 100 carats in January after finding “only” eight such stones in all of 2017. One of those five was the 910 carat (ct) Letseng Legend (named after the company’s mine in Lesotho), which it recently sold for $40 million at a special auction. Then, in March, the same company recovered a 152 ct diamond.

Lucara Diamond Corp., which operates the Kerowe mine in Botswana, found five 100 ct-plus diamonds during the first quarter. And in April, the company announced it had discovered a 472 ct diamond in the same section of the mine where it discovered the 1,100 ct Lesedi la Rona diamond two years earlier. The 472 ct is the third largest diamond to come from the mine. Lucara executives described the color as “top light brown,” which means it is likely to polish out as an M-to-O color stone.

Shortly after this discovery, Lucara mined three more 100 ct-plus diamonds, including a 327 ct rough it described as a “high-color” stone, referring to D-E-F color grades on the GIA scale. The company will sell both diamonds at a special tender auction in June.

Kerowe’s output declined 27% last year due to production problems that forced the company to shift operations away from the richest area of the mine where most of the very large diamonds have been found.

Angola’s Luo Mine yielded a 46 ct fancy pink rough in April, reported Lucapa Diamond Company, the Australia-based operator of the mine. Luo, one of the smaller mines (producing fewer than one million carats yearly) specializing in major diamonds, has produced stones as large as 404 carats. The 46 ct diamond is the largest fancy color diamond it has produced since it came onstream four years ago.

The mysterious 6.16 Fancy Dark gray-blue Farnese Blue diamond was kept in a small wooden box away from the public eye for more than two centuries. The French script on the silver plaque on the box reads: “Remarkable blue brilliant. This historical stone was offered by the Philippine Islands to Elisabeth Farnese, Queen of Spain, wife of Philippe V, great-grandfather of the Comte of Villafranca, current owner of that stone.” Photo courtesy of Sotheby's.
AUCTIONS
The royal-provenance 6.16 ct pear shape Farnese Diamond drew a top bid of $6.7 million at Sotheby’s May 15 auction in Geneva, a price well above its high estimate of $5 million. The diamond, graded Fancy Dark grayish-blue by GIA, was a gift from King Phillippe V of Spain to his bride Elisabeth Farnese after they married in 1714. After her death, the diamond passed through royal houses in Italy and Austria, most of the time hidden in a small wooden box.

At the same auction, a GIA-graded 51.71 ct D Fl Type IIa diamond sold for $9.24 million; a 14.01 ct Kashmir sapphire sold for $1.8 million; and a 9.7 ct Fancy Light purple pink diamond soared far beyond its high estimate of $672,000 to sell for nearly $2.6 million.
LAS VEGAS
The industry is anticipating respectable demand for diamonds and colored gemstones at the upcoming JCK Show in Las Vegas. Retail demand is steady in the U.S. and climbing again in China.

In the U.S., the Conference Board Consumer Confidence Index rose in April.

“Consumers’ assessment of current conditions improved somewhat, with consumers rating both business and labor market conditions quite favorably,” said Lynn Franco, director of economic indicators at the Conference Board. “Consumers’ short-term expectations also improved, with the percent of consumers expecting their incomes to decline over the coming months reaching its lowest level since December 2000 (6%). Overall, confidence levels remain strong and suggest that the economy will continue expanding at a solid pace in the months ahead.”

In China, first quarter jewelry and watch sales climbed 8% on the mainland and 22% in Hong Kong, the China and Hong Kong statistics bureaus reported. Sales at the end of the quarter were particularly strong in both regions. Source: GIA @topic:8


Title: Fancy Deep Brown-Orange CVD Synthetic Diamond Abstract: Figure 1. A face-up image showing the deep brown-orange bodycolor of a CVD-grown synthetic that has been irradiated and annealed. Photo by Robison McMurtry.

A 0.56 ct diamond (figure 1) was color graded as Fancy Deep brown-orange. The diamond was found to be a CVD-grown synthetic that had been irradiated and annealed, perhaps multiple times. DiamondView imaging (figure 2) showed the telltale striations of the CVD growth process, and the PL spectrum showed the SiV– (736/737 nm doublet) commonly found in CVD synthetics. The Vis-NIR spectrum (figure 3) showed a GR1 defect (the neutral vacancy center) and a peak at 594 nm that is commonly seen in diamonds that have been irradiated and annealed. This is in contrast to the normal irradiated and annealed CVD synthetic diamonds that show features related to nitrogen vacancies. The PL spectrum shows the NV0 (575 nm) and NV– (637 nm) peaks in relatively high concentrations compared to the diamond Raman line. In the infrared spectrum, a clear band at 1130 cm–1 and a peak at 1344 cm–1 indicate the presence of single substitutional nitrogen.

Figure 2. A DiamondView image reveals the characteristic growth striations of a CVD-grown synthetic diamond. Photo by Nicole Ahline.

Figure 3. The visible-NIR spectrum of the irradiated and annealed CVD synthetic shows the GR1 and 594 nm defects.
CVD-grown synthetic diamonds have been known to be irradiated (Fall 2014 Lab Notes, pp. 240–241; Fall 2015 Lab Notes, pp. 320–321) and also irradiated and annealed (J. Shigley et al., “Lab-grown colored diamonds from Chatham Created Gems,” Summer 2004 G&G, pp. 128–145). The irradiation and annealing performed on CVD synthetics is generally done on those with isolated nitrogen and produces a pink to red bodycolor. This color is caused by nitrogen-vacancy centers created when the vacancies produced by irradiation combine with the isolated nitrogen during the annealing process. In this case, the diamond showed a brown-orange bodycolor due to the combination of the isolated nitrogen and irradiation features. The stone in question contained isolated nitrogen, so it is possible that the intent was to create a pink to red color, but the treatment did not produce the expected results. Brown-orange color as a result of treatment has not been seen in a CVD synthetic diamond before, so the intentions of the treatment are as yet unknown. Source: GIA @topic:4


Title: Exhibition Review: Green Diamonds: Natural Radiance Abstract: Figure 1. Loose and mounted stones are part of the Natural History Museum of Los Angeles’s Natural Radiance green diamond exhibition. Left: A 4.17 ct Fancy Vivid yellowish green unmounted diamond. Center: A 1.53 ct Fancy Intense green diamond ring set in platinum. Right: An unmounted 1.92 ct Fancy Vivid green yellow diamond. Photos © Optimum Diamonds.

                      Green is among the rarest colors found in natural diamond; this hue is caused by gamma radiation while the stones are still deep within the earth. Since there are comparatively few of these specimens available, it is remarkable to find an entire exhibition dedicated to them. Green Diamonds: Natural Radiance, at the Natural History Museum of Los Angeles (NHMLA), showcases eight displays of more than 60 loose and mounted diamonds in various shades of green (figure 1). The exhibition was curated in partnership with New York–based Optimum Diamonds, which specializes in rare and exotic natural-color diamonds. The stones on display were collected over the course of 20 years as part of Optimum’s Gamma Green collection.

	Figure 2. Unmounted green diamonds on display include a 0.47 ct Fancy Deep bluish green (left), a 0.58 ct Fancy Vivid green (center), and a 1.92 ct Fancy Intense yellow green. Photos © Optimum Diamonds.

The exhibit itself is in a private room in the back of the museum’s esteemed Gem and Mineral Vault. While other gem materials are displayed in the room, the green diamonds rightfully take center stage. More than 30 loose faceted stones are on display, in hues ranging from greenish blue to green-yellow (figure 2), a valid representation given how rarely these colors are found in natural diamond. One display was set aside for chameleon diamonds, which change from their natural greenish yellow color to brown or orange when exposed to heat or light. Of particular interest among these rarest of gemstones was a 3.08 ct Fancy Dark gray greenish yellow chameleon diamond (figure 3).

	Figure 3. These two pear-shaped stones, a 3.08 ct Fancy Dark gray greenish yellow on the left and a 2.15 ct Fancy Deep brownish green yellow on the right, were included in the chameleon diamond display. Photos © Optimum Diamonds.

	Figure 4. Left: The Wild Orchid ring incorporates two green diamonds (weighing 0.86 and 0.76 ct) into a titanium setting. Right: The Caribbean earrings, inspired by the tropical locale, each have at their center a Fancy Vivid blue-green diamond weighing more than 4 ct. Photos © Optimum Diamonds.

The jewelry pieces chosen to showcase these diamonds—mostly rings—are nothing less than exquisite. While some, like the Wild Orchid ring and the Caribbean earrings (figure 4) use stones of multiple colors, shapes, and sizes to achieve a striking effect, many others use simple, classic-cut colorless stones as accents, allowing the green diamond to be the true centerpiece. Figure 5 shows two such examples: a 2.01 ct Fancy Vivid green-yellow square cut surrounded by a square border of colorless stones, and 4.94 ct Fancy Deep yellowish green oval in a timeless, elegant setting. The Nautilus ring and matching earrings merge these concepts, with a freeform design that features a Fancy Vivid blue-green stone at its center, to great effect (figure 6).

	Figure 5. Many of the jewelry pieces in the exhibit, such as the rings shown here, allow the green diamond to occupy center stage with designs that are simple yet elegant. Left: The color of the 2.01 ct Fancy Vivid green-yellow diamond is emphasized by the surrounding square border of colorless stones. Right: In this timeless ring, colorless diamonds frame the 4.94 ct Fancy Deep yellowish green center stone. Photos © Optimum Diamonds.

	Figure 6. The Nautilus ring and earrings, set in white gold, each have a Fancy Vivid green-blue diamond at its center. The diamond in the ring weighs 1.55 ct; the diamonds in the earrings are 1.04 ct and 1.20 ct. Photos © Optimum Diamonds.
The displays provide details about the general nature of diamonds and the causes of their color, along with each specimen’s carat weight. The museum notes briefly that radiation was identified as the source of the green color in 1904, when “an unnamed scientist” (Sir William Crookes) buried white diamonds in radioactive salts; there are also brief explanations of diamond geology and the nature of chameleon diamonds. It was a pleasant surprise to find this information available in both English and Spanish. However, it would have been nice to have more information on the formation and radiation of these rare stones, perhaps in the form of wall signage. The room is also rather darkly paneled and dimly lit; a brighter environment might have shown these stones to their best advantage. And while there are only a few well-known green diamonds, some basic information to educate the visitor on famous gemstones such as the Dresden Green, the Ocean Dream, and the Aurora Green would have been a welcome addition.

Green Diamonds: Natural Radiance adds a bit of panache to an already delightful trip to NHMLA. The exhibition is a must for any diamond aficionado with an eye toward color.

Green Diamonds: Natural Radiance is on view at the Natural History Museum of Los Angeles until April 1, 2018. Admission is $15 for adults; $12 for seniors 62 and over, students with school IDs, and youths ages 13–17; and $7 for children ages 3–12. Los Angeles County residents receive free museum admission Monday–Friday from 3:00 to 5:00 p.m. The museum is open from 9:30 to 5:00 p.m. seven days a week; it is closed New Year’s Day, Fourth of July, Thanksgiving, and Christmas Day. Source: GIA @topic:7


Title: Fracture-Filled Diamond with "Rainbow" Flash Effect Abstract: Figure 1. Large fractures in this diamond are exposed in high relief before treatment (left). After the fractures are filled, the same stone has a much improved apparent clarity (right). Photos by John I. Koivula.
A loose diamond submitted for a diamond grading report is evaluated and given a grade on a scale relative to each value factor. Clarity, defined as a diamond’s relative freedom from inclusions or blemishes, is graded on a scale of Flawless (least included) to I3 (most included). The most common inclusions in diamond are crystals, which are contained entirely within the stone, and fractures—also known as feathers—which are surface reaching. Various clarity treatments exist to mask or remove undesirable inclusions because high-clarity diamonds are considered more valuable. Some diamond clarity treatments are permanent, while others are not and may change drastically in appearance with time or improper care. For this reason, GIA does not issue grading reports for diamonds that have been treated with unstable, non-permanent treatments. Acceptable treatments such as laser drilling and internal laser drilling are always clearly disclosed on grading reports.

Figure 2. The classic flash effect appearance: a pink flash in darkfield lighting (left) and a complementary green flash in brightfield lighting (right). Photos by John I. Koivula.
One such unstable treatment is fracture filling. Large, deep fractures in a diamond will often appear white or reflective due to the difference in the refractive index of the diamond and the air within the fracture. In an effort to disguise this, a substance with a refractive index similar to diamond’s, such as highly refractive lead glass, is introduced into surface-reaching fractures to reduce the interference of air (figure 1). Several telltale signs, such as the flash effect, typically reveal the presence of a filled fracture. The classic flash effect displays a vivid pink color in darkfield illumination and a complementary green color in brightfield illumination (figure 2). In a different orientation in brightfield lighting, a filled fracture can also appear bright blue.

Figure 3. A face-up view of the near-colorless 1.21 ct fracture-filled square modified brilliant cut. Photo by Robison McMurtry.
A 1.21 ct near-colorless square modified brilliant diamond was recently submitted to GIA’s Carlsbad laboratory for a diamond grading report (figure 3). It was rejected for grading after examination revealed a large filled fracture. Interestingly, the flash effect looked noticeably different from the classic appearance described above. Rather than flashing a single color in darkfield lighting and a single complementary color in brightfield lighting, this filled fracture flashed multiple colors in darkfield and multiple complementary colors in brightfield (figure 4). The unusual effect may be due to a difference in ingredients used to manufacture the filling material. To the untrained eye, it could easily be mistaken for the natural iridescence very commonly seen in unfilled fractures. However, such iridescence typically appears when the viewing angle is nearly perpendicular to the fracture, while the flash effect is most visible when the viewing angle is nearly parallel to the plane of the fracture. In addition to the “rainbow” flash effect, this filled fracture showed a dendritic pattern at the fracture opening that is caused by air pockets in the filling substance (figure 5). This pattern is characteristic of incomplete fracture filling (J.I. Koivula, The MicroWorld of Diamonds, Gemworld International, Inc., Northbrook, Illinois, 2000, pp. 106–108) and provides further evidence of the treatment.

Figure 4. When viewed nearly parallel to the plane of the fracture, this filled fracture exhibits a multicolored “rainbow” flash effect in both darkfield illumination (left) and brightfield illumination (right), as opposed to a classic single-color flash effect. Photomicrographs by Nathan Renfro; field of view 2.21 mm.

Figure 5. In addition to a “rainbow” flash effect, this filled fracture displays a dendritic pattern (and its mirror reflection) at the opening of the fracture. This pattern occurs as a result of incomplete fracture filling. Photomicrograph by Nathan Renfro; field of view 1.83 mm. Source: GIA @topic:4


Title: Is the Swan Song for Argyle Pink Diamonds Close at Hand? Abstract: The 2.11 ct Argyle Everglow is the largest Fancy red diamond ever sold by Argyle at its tender sales. The Everglow was the cornerstone of Arglye’s 2017 Pink Diamond Tender that consisted of 58 stones totaling 49.39 carats. Photo courtesy of Rio Tinto/Argyle

The flow of those distinctive Argyle fancy pink diamonds may end in 2020 if prices of the more commercial stones the mine produces do not improve.

Argyle mined 17.1 million carats of diamonds last year, a 23% increase over 2016. The vast majority of its production comprises lower quality diamonds under 0.15 carats that are used in promotional jewelry – those $299 diamond studded bracelets and pendants, for example. Prices for these have declined slightly in the five years since the mining company completed its estimated $1 billion underground redevelopment.

In planning the redevelopment, the company had targeted 2020 as its closing date. However, in its original plan, Argyle had been scheduled to close in 2002 but rising diamond prices allowed Rio Tinto, its owner, to keep the mine open and, ultimately, redevelop it into an underground operation.

Closing the mine could cause economic difficulty in several cities in India that specialize in cutting Argyle goods and possibly create shortages in the very low end goods that sustain the commercial jewelry market, especially in the U.S.

The mine, however, is famous for the 100 carats or so of the fancy pink, red and other strongly colored diamonds it offers each year. Argyle selects the best of these colored diamonds for its highly publicized tender auctions. While the company does not reveal prices, they often fetch well in excess of $1 million per carat.

Last year’s October tender included some of the most spectacular fancy colored diamonds the company has offered since its first sale in 1984: a 2.11 ct Fancy red, which it named the Argyle Everglow; a 1.14 ct Fancy red; a 2.42 ct Fancy purple-pink; a 1.50 ct Fancy deep pink; and a 0.91 ct Fancy deep gray-violet. All were graded by GIA.

De Beers’ second cycle (Feb. 29-March 1) sales of $555 million reflects the company’s optimistic statements about the market. The total, which includes sight sales and individual sales to clients, is 17% below January’s total – traditionally the year’s largest – and slightly above its February 2017 sales totals. The company held the line on prices.

De Beers reported that the two largest consumer markets, the U.S. and China, both appeared strong.

Alrosa, the world’s largest producer by volume, nearly equaled De Beers’ rough sales in February with an allocation of $533 million, equaling its January sale.

Demand at the recent Hong Kong International Diamond, Gem & Pearl Show was slightly below expectations, because traffic was down from last year, even after a successful New Year’s selling season.

Despite the obvious pick-up in consumer demand, banks will certainly continue their tight rein on industry financing in the wake of the nearly $2 billion alleged fraud by Indian retailer Nirav Modi and a related diamond manufacturing and retailing company, Gitanjali. Some of Modi and Gitanjali’s issues stem from alleged defrauding of banks and Indian consumers, as well an ongoing investigation that has made international headlines. In addition, the companies are accused of involvement in “roundtripping” practices – exporting and importing the same parcels of diamonds to inflate a company’s balance sheet to obtain additional bank credit and better credit terms.

Gitanjali and Nirav Modi deny the accusations and neither company has filed for bankruptcy. Three U.S. affiliates, bridal jewelry manufacturer A. Jaffe, and jewelry manufacturers Firestar Diamond Inc. and Fantasy Inc., have filed Chapter 11 proceedings, but all expect to remain in business.

The banks are already further tightening credit, according to Indian gem dealers. Bidding at the Feb. 26 Gemfields auction of commercial and low-quality emeralds in Jaipur had fewer bidders because the investigations reduced their credit availability, the company said. Gemfields sold $10.8 million worth of emerald rough for an average of $3.08 per carat. The company said the results were satisfactory, despite the diminished bidder base. Source: GIA @topic:8