Publish Year: 2022 Title: Gemological Characteristics of Low-Temperature “Gel-Filled” Turquoise Abstract: Figure 1. Untreated rough turquoise material produced in Zhushan County, Hubei Province, China, including one piece (indicated with the dotted line) that was selected to be cut into several square pieces. Photo by Andi Zhao.
In the past decade, low-temperature “gel-filled” turquoise (X. Yating and Y. Mingxing, “Filling material and characteristic of polymer-impregnated turquoise in Anhui Province,” Journal of Gems and Gemmology, Vol. 21, No. 1, 2019, pp. 20–30) has been sold in the Chinese market. This special gel filling treatment is quite different from previous resin-filling or impregnation treatments (L. Liu et al., “Technical evolution and identification of resin-filled turquoise,” Spring 2021 G&G, pp. 22–35). The rough turquoise materials are soaked in a polymer composite gel at –10° to –15°C (without pressure) for filling and enhancement of appearance. According to the information obtained from a turquoise factory in Shiyan city, Hubei Province, the process can be generally summarized as follows:

The rough turquoise material is selected, cut, washed, and dried at about 100°C.
The material is immersed in a polymer composite gel solution, then put in the refrigerator and soaked at –10° to –15°C for 7–10 days.
The turquoise material is removed from the refrigerator and heated from room temperature to 80° at 1°C/min, followed by soaking at 80°C for four hours.
The material is further heated by ramping the temperature from 80° to 120°C at 1°C/min, followed by soaking at 120°C for eight to ten hours.
The turquoise material is then cooled from 120°C to room temperature at 3°C/min.
After removal from the furnace, the gel residue is removed by polishing off the surface layer.

Figure 2. These images show the untreated turquoise, the gel-filled turquoise, and the gel solution in glassware under normal light (A–C) and under UV light (D–F). Photos by Andi Zhao.
The authors selected a piece of rough turquoise material (figure 1) produced in Zhushan County in Hubei Province, China, and cut it into several square pieces. According to the above treatment process, the turquoise was filled using the gel solution provided by the turquoise factory in Hubei. The material before treatment (N-1) was light whitish blue, with uneven color distribution, and black impurities were locally distributed. After treatment, the material’s color deepened to a more desirable blue-green and became more uniform (figure 2), still retaining the original black impurities. After polishing, the surface of the gel-filled turquoise had a waxy luster and the hydrostatic specific gravity changed from approximately 2.32 to 2.21 due to the lower SG of the gel (approximately 1.00). The turquoise before treatment showed medium-light bluish white fluorescence with an abundance of white spots. After treatment, it showed uniform medium bluish white fluorescence (figure 2) under long-wave UV fluorescence. The turquoise was inert to short-wave UV before and after treatment. The light yellow gel solution showed a strong bluish white fluorescence along the edge of the glassware under long-wave UV and was inert under short-wave UV.

Figure 3. FTIR spectra of the gel, untreated turquoise, and low-temperature gel-filled turquoise. The characteristic peaks for gel-filled turquoise are a series of peaks at 2966, 2928, 1727, 1637, 1456, 1405, 1378, 1324, and 1297 cm–1 that are caused by the gel.
Fourier-transform infrared (FTIR) spectra of the gel and turquoise samples (before and after treatment) are shown in figure 3. Typical peaks for turquoise were observed, namely two absorption peaks at 3509 and 3463 cm–1 caused by the stretching vibration of hydroxyls (OH) (Q. Chen et al., “Turquoise from Zhushan County, Hubei Province, China,” Fall 2012 G&G, pp. 198–204). Due to strong hydrogen bonding associated with the hydroxyl groups, the absorption peaks are relatively sharp. The absorption peaks at 3288 and 3077 cm–1 caused by OH stretching of water molecules are relatively flat, while the peak associated with the bending vibration of water is near 1637 cm–1 and the intensity of the absorption peak is relatively weak. There are four absorption peaks produced by the PO4 stretching vibration between 1000 and 1200 cm–1, which appear near 1153, 1006, 1056, and 1010 cm–1. In addition, the gel-filled turquoise showed a weak absorption peak (2928 cm–1) caused by a CH2 stretching vibration and a strong stretching vibration peak (1727 cm–1) caused by C=O (Yating and Mingxing, 2019). A series of weak small absorption peaks also appeared at 1456, 1324, and 1297 cm–1. These spectral peaks are consistent with the FTIR spectra of the gel. The spectral peaks can also be used to distinguish between untreated and gel-filled turquoise. Gas chromotography–mass spectrometry identified the main components of the gel as methyl isocrotonate (C5H8O2, 46.05 wt.%), cyclooctatetraene (C8H8, 35.8 wt.%), and oxirane (C2H4O, 5.93 wt.%). @topic:3


Publish Year: 2022 Title: Barite-Calcite Composite as Imitation “Wulanhua” Turquoise from Hubei Province, China Abstract: Figure 1. The bracelet submitted as “Wulanhua” turquoise. Photo by Shu-Hong Lin.
“Wulanhua” turquoise is well known in the Taiwan and mainland China market. It has also been called “Ulan flower” turquoise in previous publications (L. Liu et al., “Unique raindrop pattern of turquoise from Hubei, China,” Fall 2020 G&G, pp. 380–400). The term “Wulanhua” is a Chinese transliteration that means black orchid, and it usually refers to turquoise of medium dark to very dark blue color with a black spiderweb pattern found in Hubei Province.
A bracelet recently submitted to Taiwan Union Lab of Gem Research (TULAB) as Wulanhua turquoise (figure 1) contained dark blue opaque beads with a black spiderweb pattern on the surface. The spot refractive index of these beads was about 1.62–1.63, close to that of turquoise. EDXRF analysis determined that the composition of the beads was inconsistent with that of turquoise (CuAl6(PO4)4(OH)8•4H2O). Instead, it was composed mainly of barium (Ba) and calcium (Ca).

Figure 2. A bead from the bracelet was cut into two halves. One half was immersed in 95% ethanol for 72 hours, clearly extracting the blue dye. Photos by Yu-Ho Li.

Figure 3. Raman spectra comparisons between the bead, the blue dye precipitate, and those of barite and calcite from the RRUFF database suggest that the bead consisted of barite, calcite, and blue dye. The stacked spectra are baseline-corrected and normalized.
To further identify the composition, Raman spectra (785 nm laser) were analyzed and compared with those from the RRUFF database. The beads displayed mixed spectra of barite, calcite, and other unknown materials. With the consent of the client, a bead was cut into two halves and polished for more testing. One half was immersed in 95% ethanol for 72 hours to extract the dark blue dye (figure 2). After the ethanol volatilized, the blue precipitate was analyzed with Raman spectroscopy and the spectrum was compared with that of the bead and the spectra from the RRUFF database. Raman analysis and the extraction experiment revealed that this material was composed of barite and calcite with an unidentified blue dye (figure 3). Microscopic observation of the cross section suggested that the beads were made of irregularly shaped barite and barite with minor calcite particles with an unknown black filling as a bonding material (figure 4).

Figure 4. The cross section of one bead showed irregularly shaped barite and barite with minor calcite particles, along with a black filling that could be some unknown bonding material. Photomicrograph by Shu-Hong Lin; field of view 8.56 mm.
The beads could be defined as a composite material made of barite (BaSO4), calcite (CaCO3), and blue dye. While visual observation and refractive index might not be enough to distinguish these beads from true Wulanhua turquoise, Raman spectroscopy and EDXRF analysis were able to reveal their true identity. @topic:3


Publish Year: - Title: Revealing “The Angel in the Stone”: The Largest Known Square Cushion-Cut Tsavorite Abstract: Figure 1. The 283.74 ct rough tsavorite was mined in Merelani, Tanzania, by Bridges Tsavorite. Photo by Robert Weldon/GIA, courtesy of Bruce Bridges.

More than 50 years after Campbell Bridges discovered the green grossularite garnet later named tsavorite, the company that bears his name carries on his legacy of ethical sourcing and mine-to-market transparency. At the 2019 AGTA Tucson gem show, Bridges Tsavorite unveiled the largest known square cushion-cut tsavorite, weighing 116.76 ct. In March 2018, a GIA team traveled to Bridges Tsavorite’s Tucson office for a look at world-renowned gem cutter Victor Tuzlukov’s approach to cutting this rare gem.
The 283.74 ct rough stone (figure 1) was mined by Bridges Tsavorite in Merelani, Tanzania, in September 2017. Bruce Bridges, the company’s CEO and son of the late Campbell Bridges, told us that the rough was extremely clean for its size. It had several very well-terminated euhedral faces, unusual for tsavorite, which typically has more fragmented face formation.
The company had already received many inquiries from around the world about purchasing the stone post-cutting. Bridges said the buyer would likely be a knowledgeable collector or a jewelry connoisseur; retail jewelers rarely purchase stones of this value except on request from a high-end client.
Bridges Tsavorite sorts and cuts all of its production in-house. Bridges said they have always prided themselves on having a transparent mine-to-market supply chain. “The public nowadays really wants to know more about a gemstone: Where did it come from? How did it get from raw to cut?” he said. “I’m really happy about documenting the entire process, from rough to finished product.”

	Bruce Bridges shows the rough tsavorite and talks about the importance of ethical sourcing.

Along with the rough stone, Bridges showed us two cut tsavorites (figure 2): a 31.57 ct square cushion cut and a 58.52 cushion cut. Tuzlukov had just finished cutting the 31.57 ct tsavorite (figures 3 and 4). Planning the cutting process took six weeks; he then spent five days cutting the stone, working from 9 to 11 hours each day. Bridges said that along with the rough, these were the three finest tsavorites he had ever seen in their respective sizes. For Tuzlukov, cutting the 31.57 ct stone was a timely preparation for cutting the larger square cushion cut.

Figure 2. This 58.52 ct cushion cut and 31.57 ct square cushion cut, along with the 283.74 ct rough, were the three finest tsavorites in their respective sizes that Bruce Bridges had ever seen. Photo by Duncan Pay.

Figure 3. The 31.57 ct square cushion-cut tsavorite and schematic diagrams offer a glimpse into the cut planning process for the large rough tsavorite. Photo by Duncan Pay.

Figure 4. Victor Tuzlukov examines the 31.57 ct square-cushion-cut tsavorite. Photo by Duncan Pay.

	Bridges tells us about the 31.57 ct square cushion-cut and 58.52 ct cushion-cut tsavorites.

“Somebody said ‘I saw an angel in the stone and cut until I let him be free,’” Tuzlukov said. “I also try to see something inside the stone.”
Bridges and Tuzlukov began discussing the approach to cutting the 283.74 ct rough in early February 2018. Tuzlukov showed us on the rough tsavorite where he envisioned the table, the crown, and the pavilion. He said sometimes he knows immediately upon looking at a rough stone what the cut stone will look like (figure 5). Other times he thinks about it “for months or longer.” His approach to cutting gemstones is undeniably metaphysical. “I try to join my consciousness with the stone,” he said. “I try to explain to him that we go to perfection together. Sometimes when I get full contact with the stone, the stone begins to help me. Not by words—just by feeling. I feel when I have to stop when cutting.”

Figure 5. Left: Tuzlukov examines the rough tsavorite. Right: Another view of the rough, with the 58.52 ct cushion cut and 31.57 ct square cushion cut. Photos by Duncan Pay.
Originally from Russia, Tuzlukov lives in Bangkok, where he facets top-quality gemstones, creates original designs, and teaches faceting at the Gem and Jewelry Institute of Thailand. He worked as a marine navigator and an economist before being introduced to gemstone cutting by a friend of a friend. He obtained his G.G. from GIA in Moscow and began faceting gemstones in 1998. In 2006 he participated in the United States Faceters Guild Competition for the first time, and in 2010 he won the International Individual Faceting Championship in Australia (with a world record of 299.17 out of 300 points). Later that year he founded the Russian Faceters Guild and the faceting competition the Russian Open.
Tuzlukov said he tells his students “in the worst case you should be just two, you and the stone. In the best case, you should be one.” Sometimes he starts cutting, and then stops and comes back after some time—perhaps weeks—because he has not achieved what he calls “full contact” with the stone.

	Tuzlukov tells us about his approach to cutting.

Tuzlukov used the 3D model of the rough tsavorite to cut a test stone from yttrium aluminum garnet (YAG), a synthetic material. Angles and indices were calculated following the shape of the rough to save as much weight as possible, and were adjusted to account for YAG’s refractive index, which is higher than tsavorite’s. After the YAG stone was cut, the real work began.
Tuzlukov began to cut the tsavorite during our visit (figure 6). The remainder of the cutting was accomplished over the course of about a month.
“The material is amazing,” Tuzlukov said. “It’s not only a pleasure but an honor for me to cut this.”

Figure 6. Tuzlukov touches the rough tsavorite to the lapidary wheel for the first time. Photo by Duncan Pay.

	Tuzlukov begins to preform the rough tsavorite.

At the AGTA show, Bridges said the tsavorite (figure 7) could be a once-in-a-lifetime stone. Despite seeing most of the finest tsavorites in the world above 20 carats, he had never seen one comparable to this size in a square cushion cut. The square cushion and round cuts are the rarest shapes for tsavorite because the rough typically lends itself better to other shapes. Square cuts in particular result in the greatest loss of weight in cutting, he said. The tsavorite also has the distinction of being the largest tsavorite, and the largest gemstone of any kind, cut in the United States.

Figure 7. Victor Tuzlukov’s cutting process yielded a 116.76 ct square cushion cut, one of the rarest cuts for tsavorite. Photo by Robert Weldon/GIA, courtesy of Bruce Bridges. @topic:2


Publish Year: 2014 Title: Natural-Color Tanzanite and Yellow Sapphire – Tucson 2014 Abstract: Figure 1. These large, reportedly unheated tanzanites possess fine color. Photos by Eric Welch; courtesy of Advanced Quality.

              At the GJX show, Kobe Sevdermish (Advanced Quality, Ramat Gan, Israel) displayed fine unheated tanzanite (figure 1), untreated yellow sapphire, and heated pink zircon.

While it is easier to buy unusual-colored tanzanite rough today, the material still is not available in abundance. Sevdermish informed us that what he calls “fancy-color” tanzanite comes from the same area as the familiar blue to bluish purple tanzanite. The rough pieces he displayed in Tucson had greenish, golden, green blue, pink, and purplish pink colors. The rarest are greens, followed by golden hues. These stones were best sellers for the company in 2013.

	Kobe SevdermishAdvanced Quality, Ltd.

	In these three videos, Israeli dealer Kobe Sevdermish introduces us to the subtle beauty of unheated tanzanite, bright yellow African sapphire much in demand among his clientele as a fancy color diamond substitute, and the rich earthy colors of heated zircon from Tanzania.
According to Sevdermish, the U.S. market is full of “regular” heated tanzanite, and people are looking for something unique. Clients are especially taken with sets where each stone displays a slightly different color. In his opinion, the luster of the unheated stones is significantly better. Sevdermish ensures that no heating is performed on any of the rough he selects. All stones are polished at the company’s factory in Bangkok.

After describing a large piece of highly transparent rough that took a week to purchase, Sevdermish showed us the two significant pieces cut from it: a 50.61 ct green-blue oval and a spectacular 19.80 ct greenish blue heart with arresting green and blue green pleochroism cut from the top part of the crystal.

	Figure 2. Precision-cut unheated yellow sapphire sold well to buyers looking for yellow diamond substitutes. Photo by Eric Welch; courtesy of Advanced Quality.
He called our attention to precision-cut unheated yellow sapphires (figure 2) arranged as sets or as precisely cut calibrated shapes, including ovals, pears, and princess cuts. Sevdermish described this corundum as a “true canary color,” which is unusual in a natural-color sapphire. He said most of the strong yellow sapphire on the market is either heated or beryllium-treated.

All the rough is carefully selected for color consistency in order to avoid greenish or grayish hues. Sevdermish estimated they select about 5% of the rough production, suitable for cutting into 2–5 mm finished stones, from a small mine in Africa. Material for 0.50 or 1 ct sizes is very rare. Sevdermish said his clients like the material because its clarity, color, and polish give it the look of fancy-color diamond.

	Figure 3. These heated Tanzanian zircons displayed a range of warm pinkish to yellowish brown colors. Photo by Eric Welch; courtesy of Advanced Quality.
Finally, Sevdermish showed us what he described as “fancy vivid” pink zircon from Tanzania (figure 3). The zircon was heat-treated, lightening the original color of the rough to reveal pinks with cinnamon tints. Further heating lightens the color a little more, producing very bright, lively stones. The only downside, Sevdermish remarked, is the name “zircon.” Customers tend to confuse the name with “cubic zirconia,” which makes them reluctant to purchase the gems until they understand that zircon is a natural stone. @topic:2


Publish Year: - Title: Characterization of Blue Sapphires from the Mogok Stone Tract, Mandalay Region, Burma (Myanmar) Abstract: Iridescent arrowhead needles and thin film, a characteristic inclusion found in Mogok Burmese blue sapphires.
Oblique illumination, field of view 1.80 mm. Photo: C. Khowpong © GIA.

The Mogok Stone Tract of central Myanmar (Burma) is one of the world’s most famed sources of colored stones, particularly ruby, sapphire, and spinel. Researchers from GIA’s Bangkok laboratory recently investigated 69 blue sapphires from the northern, western, eastern and northwestern areas of Mogok. They performed microscopic examination, FTIR and UV-Vis-NIR spectroscopy, and chemical analysis by LA-ICP-MS to establish identifying characteristics and properties of blue sapphires from Mogok.

The results are available in a study titled “Characterization of blue sapphires from the Mogok Stone Tract, Mandalay region, Burma (Myanmar).” The authors concluded that blue sapphires from Mogok possess a variety of internal characteristics and chemistry features that may support their identification as Burmese. @topic:2


Publish Year: - Title: Bench Tip #17: Avoid Stone Loss with Quality Assurance Benchmarks Abstract: Avoiding Stone Loss

Fine jewelry represents much more than its trade value in diamonds, gemstones and precious metals. It is a personal representation of the owner’s lifestyle, status, emotion, recognition, commitment and more. That significance only amplifies how devastating the loss of a gemstone is for the owner. Even one missing accent stone renders the jewelry unwearable. Loss of a significant gemstone will also impact the retailer who sold the piece and the manufacturer who engineered and produced it.

The loosening, damage or loss of gemstones in jewelry can be attributed to two factors: poor workmanship or the absence of benchmarking standards for setting. Benchmarks are specific parameters used to compare and evaluate the acceptability of a finished product for market.

Stone loss can be avoided. Inspecting each piece and comparing it against established benchmarks for signs of vulnerability in normal wear gives the jeweler/manufacturer an opportunity to address potential problems before jewelry is offered for sale. Adopting consistent task-specific benchmarks encourages sound design and good workmanship, assuring the quality of jewelry for the consumer.

Examples of the quality assurance benchmarks presented here are for setting round brilliant gemstones in traditional angled prongs.

	This drawing shows benchmarking criteria for angled prongs on a center stone.
Prong Setting Benchmarks – Traditional Angled Prongs

A:  Prong angle is 70-80 degrees.

B:  Sufficient prong thickness is needed to secure the stone in place, so 40-50% of the metal is removed from the prong thickness at the bearing.

C:  Diamond is seated level in the bearing just above the gallery wire. There are no gaps in any bearing – the bearing is the cut made in a prong and must precisely fit the stone contour when properly set. Any gaps will allow the stone to move or loosen.

D:  Finished prong height is 75-85% of table height. Ample prong height allows the prong to hold up through normal wear.

E:  Prong contact is 33-50% of total crown distance. Adequate prong contact over the crown is critical to a stable setting.

F:  Prongs are rounded, polished and consistent in size and shape.

Potential Errors in Workmanship for Traditional Angled Prongs
Example 1: Using benchmarking quality assurance benchmarks, you will note a bearing was not cut (lower blue arrow) and the diamond is not seated. Prong contact is insufficient (upper blue arrow) and barely secures the diamond.

	This center stone has no bearing.
Example 2: The bearing does not conform to the crown and pavilion angles of the diamond, so there are large gaps. Too much metal was removed from the prong thickness.

	This prong is overcut and there is visible open space at the bearing.
Understanding what to look for and following consistent quality assurance practices will enable our industry to ensure that our global consumers have the best possible jewelry experiences. @topic:6


Publish Year: - Title: Bench Tip #7: A Modified Tool to Bezel-Set Round Faceted Stones Abstract: Bezel-set round faceted stones

This is a follow-up to Bench Tip #6, “Using a Split Mandrel for Finishing Fabricated Round Bezels,” which showed you how to modify a standard split mandrel to make an effective holding device to finish several fabricated bezels of the same dimensions. The same split mandrel can also be adapted into an efficient tool for setting multiple round faceted stones into those bezels.

Secure the modified split mandrel in a ring clamp. Insert a 3.5 mm ball bur into the No. 30 hand piece of a flex shaft and burr a hollow into the top center of the mandrel, cutting to a depth of about 2.0 mm. Follow with a 2.5 mm ball bur, centering and burring to a total depth of around 3.0 mm. You will create a void that provides clearance for the pavilion and culet of each stone to be set.

	Further modification of the split mandrel for setting is required. Using two ball burs, create a clearance for the pavilion during setting.
The total depth of the bezel must be at least 4.0 mm to accommodate the depth of the stone when set. Choose a finished bezel and position it on the mandrel. Secure the mandrel in a ring clamp. Measure the stone to be set and select the proper size setting bur. You will be cutting the depth of the bearing so that the top of the bezel flange is no less than 50 percent of the crown height. Cut the bearing and check the fit of the stone to make sure it is level and at the correct depth for setting.

	The depth of the bearing should be 50 percent or more, depending on the cut and proportions of the stone.
Remove the mandrel and bezel from the ring clamp and tighten it in the hand piece on your flexible shaft. While spinning the hand piece, use a file to bevel and reduce the thickness of the bezel flange. Clean any debris from the bezel and place a small amount of wax in the bearing to help hold the stone during the setting process. Pack and level the stone.

The bezel contact should be no less than 10 percent of the crown distance, which is the dimension along the surface of the crown from girdle (0%) to table (100%). Rotate the hand piece as you use a burnisher to apply pressure to the beveled edge of the flange, pushing the metal over the stone. Look closely to make sure there is complete 360 degree contact against the crown.

	The amount of metal burnished over the crown should be 10 percent or more of the crown distance.
The completed bezels are ready to become a part of your fine jewelry creations. If the stones you use can take heat, the bezels can be soldered into jewelry by the traditional torch method. If they are vulnerable to heat, use a laser welder to set the bezels in place. @topic:6


Publish Year: 2013 Title: The “Glet Filling”: The Filling of the Cracks in Precious Stones Under Scrutiny Abstract: This short article discusses several important aspects of fracture filling in colored stones and diamonds: the difference in market value between included and filled stones, especially in high-quality goods; the impact of nondisclosure within the supply chain; different methods of filling and their limitations; and methods of detection.

Several similar methods of filling diamond cracks (“glets”) have been developed under such names as Yehuda and Koss (Israel) and Diascence, Genesis Enhanced, and Goldman Oved (New York). One of the filling methods discussed in more detail, the Koss system created more than ten years ago, limits the rainbow or “flash” effect, the yellow-orange color flashing into electric blue under darkfield microscopy) characteristic of many other filling methods.

Regardless of the method, the visual improvement achieved from filling cracks with oils or the modern vitreous, high-RI materials is temporary: After a few months or a few years, the tears and cracks become visible. Fillers degrade with time and by environmental conditions. Some dry out to reveal noticeable residue; others deteriorate with exposures to ultrasound, ultraviolet, heat, acids, and chemical cleaners.

Several methods of detecting fillers are briefly mentioned. Gemologists commonly use magnification to observe bubbles, filler textures, the flash effect, and filler deterioration. Advanced methods such as scanning electron microscopy, X-ray fluorescence analysis, and Raman spectroscopy easily reveal the presence of filled glets.

Abstracted by Edward R. Blomgren @topic:10


Publish Year: 1983 Title: The Identification of Turquoise by Infrared Spectroscopy and X-Ray Powder Diffraction Abstract: A combination of infrared spectroscopy and X-ray powder diffraction methods is suggested for the identification of natural, treated, and synthetic turquoise as well as imitation turquoise. Both techniques require powdering only a very small quantity of the specimen (approximately 3 mg), which means minimal damage to the piece. New experimental results on treated turquoise and imitation turquoise are given. @topic:3


Publish Year: - Title: The “Glet Filling”: The Filling of the Cracks in Precious Stones Under Scrutiny Abstract: This short article discusses several important aspects of crack-filling in colored stones and diamonds: the differences in market values between included and filled stones, especially in high quality goods; the impact of nondisclosure within the supply chain; a brief discussion of different methods of filling and their limitations; and, finally, methods of detection.

Several similar methods of filling cracks (“glets”) have been developed under such names as Yehuda and Koss (Israel) and Diascence, Genesis Enhanced, and Goldman Oved (New York). One of the filling methods discussed in more detail, the Koss system developed at least ten years ago, limits the rainbow or “flash” effect (the yellow-orange color flashing into electric blue under dark field microscopy) characteristic of many other filling methods, and useful for identifying the presence of a filler.

Regardless of method, the visual improvements achieved from filling cracks with oils or the more modern vitreous, high-RI materials is temporary; eventually the tears and cracks become visible after a few months or years. Fillers degrade with time and by environmental conditions. Some dry out to reveal noticeable residue; others deteriorate with exposures to ultrasound, ultraviolet, heat, acids, and chemical cleaners.

Several methods of detecting fillers are briefly mentioned. Gemologists commonly use magnification to observe bubbles, filler textures, the flash effect, and effects of deterioration. Advanced instruments such as the scanning electron microscope, X-ray fluorescence analysis, and Raman spectroscopy easily reveal the presence of filled glets.

Abstracted by Edward R. Blomgren @topic:10


Publish Year: - Title: Bench Tip: Avoid Stone Loss With Quality Assurance Benchmarks Abstract: Bench Tip: Avoid Stone Loss With Quality Assurance Benchmarks

Fine jewelry represents much more than its trade value in diamonds, gemstones and precious metals. It is a personal representation of the owner’s lifestyle, status, emotion, recognition, commitment and more.

That significance only amplifies how devastating the loss of a gemstone is for the owner. Even one missing accent stone renders the jewelry unwearable. Loss of a significant gemstone will also impact the retailer who sold the piece and the manufacturer who engineered and produced it.

The loosening, damage or loss of gemstones in jewelry can be attributed to two factors: poor workmanship or the absence of benchmarking standards for setting. Benchmarks are specific parameters used to compare and evaluate the acceptability of a finished product for market.

Stone loss can be avoided. Inspecting each piece and comparing it against established benchmarks for signs of vulnerability in normal wear gives the jeweler/manufacturer an opportunity to address potential problems before jewelry is offered for sale. Adopting consistent task-specific benchmarks encourages sound design and good workmanship, assuring the quality of jewelry for the consumer.

Examples of the quality assurance benchmarks presented here are for setting round brilliant gemstones in traditional angled prongs.

	This drawing shows benchmarking criteria for angled prongs on a center stone.

Prong Setting Benchmarks – Traditional Angled Prongs

A: Prong angle is 70-80 degrees.

B: Sufficient prong thickness is needed to secure the stone in place, so 40-50% of the metal is removed from the prong thickness at the bearing.

C: Diamond is seated level in the bearing just above the gallery wire. There are no gaps in any bearing – the bearing is the cut made in a prong and must precisely fit the stone contour when properly set. Any gaps will allow the stone to move or loosen.

D: Finished prong height is 75-85% of table height. Ample prong height allows the prong to hold up through normal wear.

E: Prong contact is 33-50% of total crown distance. Adequate prong contact over the crown is critical to a stable setting.

F: Prongs are rounded, polished and consistent in size and shape.

Potential Errors in Workmanship for Traditional Angled Prongs

Example 1: Using benchmarking quality assurance benchmarks, you will note a bearing was not cut (lower blue arrow) and the diamond is not seated. Prong contact is insufficient (upper blue arrow) and barely secures the diamond.

	This center stone has no bearing.

Example 2: The bearing does not conform to the crown and pavilion angles of the diamond, so there are large gaps. Too much metal was removed from the prong thickness.

	This prong is overcut and there is visible open space at the bearing.

Understanding what to look for and following consistent quality assurance practices will enable our industry to ensure that our global consumers have the best possible jewelry experiences. @topic:8


Publish Year: 2023 Title: Spotted Diamond Abstract: Numerous metal sulfide crystals scattered throughout a 3.05 ct Fancy Light gray diamond. Photomicrograph by Michaela Damba; field of view 14.52 mm.
The author recently examined a large 3.05 ct Fancy Light gray diamond featuring dark crystals scattered throughout (see above). It had a clarity of I3, the lowest grade for gem-quality diamond, but demonstrated that low-clarity diamonds can sometimes be more intriguing than their higher-clarity cousins. Stones with numerous eye-visible crystal inclusions such as this are sometimes referred to in the trade as “salt and pepper” diamonds.
Numerous attempts to identify the dark crystals using Raman spectroscopy proved unsuccessful. X-ray fluorescence revealed high levels of iron, leading the author to conclude that they were likely metal sulfides rather than graphite. This presumption has not been confirmed with Raman spectroscopy. @topic:10


Publish Year: 2023 Title: Breyite in Diamond Abstract: A well-formed colorless breyite crystal reminiscent of a stone making a splash in water. Photomicrograph by Aprisara Semapongpan; field of view 1.07 mm.
The author recently examined a 0.71 ct D-color type IaB diamond with an interesting inclusion reminiscent of a stone splashing in water (see above). Raman analysis identified the well-formed colorless transparent crystal as breyite (CaSiO3), a calcium-rich silicate mineral commonly found in sublithospheric or superdeep diamonds. It was hypothesized that this diamond formed in the lower part of the transition zone or the lower mantle beneath the earth’s crust.
Since the majority of diamonds in the jewelry industry come from the lithosphere, each one provides a window into Earth’s intricate geology. Inclusions such as this one serve as a reminder that beauty and flaws may coexist peacefully, whether they add to a diamond’s charm or provide scientific insight. @topic:10


Publish Year: 2023 Title: “Snail” in Diamond Abstract: This “snail” inclusion was viewed through the upper half facet of a 4.00 ct near-colorless diamond. The purple-red “shell” was identified as pyrope garnet, while the green “body” was determined to be diopside. Photomicrograph by Christopher Vendrell; field of view 1.99 mm.
While different types of inclusions often occur independently within diamond, it is quite rare to find more than one occurring simultaneously, let alone in contact with each other. In the figure above we have a unique example of a purple-red pyrope garnet crystal and green diopside crystal suspended together, having been captured within this natural 4.00 ct near-colorless diamond during formation. Such inclusions can be utilized to verify what environment a diamond may have formed in. In this case, the diamond’s genesis was likely in an ultramafic peridotite environment. The appearance of this unique inclusion series is playfully reminiscent of a snail. @topic:10


Publish Year: 2023 Title: Musical Diamond Abstract: A crystal with a stress halo and a smaller adjacent crystal resembles a dotted quarter note. Several reflections of such crystals with stress fractures are visible. Photomicrograph by Michaela Damba; field of view 2.90 mm.
Recently the author examined a 0.95 ct diamond with a special note. It only took one and a half beats to discover a dark crystal with a straight stress cleavage crack shaped like a dotted quarter note (see above).
Crystals, cleavages, and other inclusions are common occurrences that impact a diamond’s clarity grade. This diamond received a clarity grade of SI1, or slightly included with inclusions noticeable to a skilled grader at 10× magnification. @topic:4


Publish Year: 2015 Title: Diamond Slices Abstract: Figure 1. These AGTA Spectrum Award–winning earrings, designed by Michael Endlich, incorporate three matched pairs of diamond slices totaling 7.07 carats into a platinum setting. Photo courtesy of Michael Endlich.

Gem and mineral slices were very popular at this year’s Tucson shows, with opaque, translucent, clear, included, rough-edged, and finely shaped slices found in every color and price point. Materials such as fossilized coral, rutilated quartz, lacy agates, labradorite, chalcedony, watermelon tourmaline, sapphire, and diamond were on display. A wide variety of sizes were available as well, with pieces measuring several centimeters in diameter finding their way into dramatic necklaces, while some high-end jewelry and collector pieces used extremely thin and small gem slices.

Notably, the third-place winner in the bridal category of the 2015 AGTA Spectrum Awards was a pair of platinum and diamond earrings designed by Michael Endlich, featuring three pairs of diamond slices in addition to several pavé-set diamonds (figure 1). Endlich finds this gem material unusual, exciting, and subtle. Most of his clients have never seen these slices and are fascinated once they realize they are looking at diamonds. He goes through thousands of slices to select those he will incorporate into pieces. He particularly likes slices with patterns, such as concentric squares. This material is relatively new to the marketplace, and he first came upon it six years ago. Even though more diamond dealers offer them today, few slices have the distinct patterns Endlich looks for.

At the GJX show, Punya Malpani (Dynamic International, Hong Kong) discussed the diamond slice market with us and shared some particularly eye-catching and rare examples. He noted that the price of these goods has gone up approximately 20× in the past decade, as jewelry designers continue to go beyond traditional faceted gem shapes. There is also a strong collectors’ market for this material, as the unique nature of each piece adds to its appeal. In fact, there are very few larger slices of diamond in the marketplace, because the outer “skin” from the rough material was generally discarded before this niche market was identified. Unlike faceted diamonds, inclusions increase the value of slices, especially if they are unusual, striking, and highlight growth patterns.

Diamond slices today are mainly cut by laser and can vary widely in diameter and thickness, though diameters greater than one centimeter are difficult to come by, as rough in that size is much rarer. Many slices are slightly faceted to add some sparkle to the finished piece. Most of the diamond slices maintain the rough outline, as this can add to the appeal, but some are shaped into fanciful and matched sizes such as the “snowflakes” Malpani showed us.

Three-rayed “trapiche” diamond slices are among the most scarce and striking, as they contain a recognizable radiation-symbol pattern (figure 2). These are only found about once in a couple of thousand slices, and even then it is rare to find distinct coloring. The collection shown in the photo took years to assemble.

Figure 2. The three-rayed “trapiche” pattern is found in less than 0.1% of diamond slices, and rarely is it so distinct. The collection of nine slices, including these four samples, took years to assemble. Photo by Jennifer Stone-Sundberg, courtesy of Dynamic International.
Malpani’s most prized slices are the matched pair of large colorless diamond slices with dramatic white patterning (figure 3). These two pieces, separated from a skin cut of a large piece of rough, date back about 20 years. This is unusual, as such slices were not retained in the past.

Figure 3. These two large colorless diamond slices from the same piece of rough show dramatic patterning. Photo by Duncan Pay, courtesy of Dynamic International.
It appears that the use of gem slices in jewelry has penetrated the high-end market. Since diamond is clearly a prominent material capitalizing on this gem “cut” with natural appeal, we can expect this trend to continue. @topic:10


Publish Year: 2018 Title: Diamond Identification Abstract: Figure 1. The canary yellow diamonds from this study showed much lower concentrations of isolated nitrogen than regular type Ib yellow diamonds, which usually show brownish and greenish hues linked to plastic deformation. Photo by Sood Oil (Judy) Chia.

Canary Yellow Diamonds
Wuyi Wang1 and Terry Poon2
1GIA, New York
2GIA, Hong Kong
Isolated nitrogen is one of the major defects in producing yellow color in natural diamonds. In regular type Ib yellow diamonds, isolated nitrogen is normally the dominant form, with limited aggregations in A centers (nitrogen pairs). Type Ib diamonds normally experienced strong plastic deformations. In addition to vacancy clusters, many other optic centers were introduced during annealing over their long geological history, such as GR1, NV, and H3 centers. Diamonds from the Zimmi area of West Africa are a typical example (Smit et al., 2016). As a result, clear brownish and greenish hues are common among these diamonds, so most do not possess true “canary” yellow color. Here we studied more than 2,000 diamonds with real canary yellow color. Their color origin and relationship with type Ib diamonds were explored.
Sizes of the studied diamonds ranged from 0.01 to about 1.0 ct. They showed pure yellow color, with grades of Fancy Intense or Fancy Vivid yellow. Infrared absorption analysis showed that they were all type IaA with very high nitrogen concentrations, but a very weak absorption from isolated nitrogen at 1344 cm–1 was detected in all samples. Concentration of isolated nitrogen was estimated at ~2–3 ppm. This isolated nitrogen created smooth absorption in the ultraviolet-visible (UV-Vis) region, increasing gradually to the high-energy side. No other defects were detected using UV-Vis absorption spectroscopy, which explained the pure yellow color we observed. Fluorescence imaging revealed multiple nucleation centers with dominant green color, which was attributed to the S3 defects confirmed through photoluminescence analysis. Compared with natural type Ib diamonds, an outstanding feature of the studied samples is the absence of plastic deformation. For this reason, other vacancy-related defects were not introduced to these diamond lattices over the geological period after their formation.
Sulfide inclusions are common in type Ib diamonds, but they were not observed in these canary stones. Instead, some calcite inclusions were observed. All the observations from this study indicated that the canary diamond samples were formed in a different geological environment than type Ib diamonds.
REFERENCE
Smit K.V., Shirey S.B., Wang W. (2016) Type Ib diamond formation and preservation in the West African lithospheric mantle: Re-Os age constraints from sulphide inclusions in Zimmi diamonds. Precambrian Research, Vol. 286, pp. 152–166, http://dx.doi.org/10.1016/j.precamres.2016.09.022
Addressing the Challenges of Detecting Synthetic Diamonds
David Fisher
De Beers Technologies, Maidenhead, United Kingdom
The dream of growing synthetic diamonds existed for many centuries before it was achieved in the 1950s. The development of techniques to identify synthetic diamonds and enable their reliable separation from natural diamonds has not had the luxury of centuries to work with. Since the early reports on the characteristics of laboratory-grown stones, scientists have been working steadily to establish and improve the means of detection. For many years the De Beers Group has been developing equipment for rapidly screening and testing for potential synthetic and treated diamonds as part of a strategy aimed at maintaining consumer confidence in natural untreated diamonds. This work has been underpinned by extensive research into defects in natural and synthetic diamond, either conducted within De Beers’ own facilities or through financial and practical support of research in external institutions.
Key to any detection technique for synthetic diamonds is a fundamental understanding of the differences between them and natural diamonds. This could take the form of differences in the atomic impurity centers or differences in the spatial distributions of these centers brought about by very significant distinctions in the growth environments. The former was used in the development of the DiamondSure instrument that, among other things, detects variance differences in the absorption spectra due to the presence or absence of the N3 feature. This absorption is from a nitrogen-related defect that is usually only produced in nitrogen-containing diamonds by extended periods at relatively high temperatures—that is, conditions generally experienced by natural diamonds. Growth-related differences in impurity distributions can be very accurately imaged using the DiamondView instrument. Short-wave ultraviolet (UV) light is used to excite luminescence from a very thin layer of diamond near the surface to give images free from the blurring encountered with more common longer-wavelength excitation sources. DiamondView has, since its launch, provided the benchmark for the detection of synthetic diamonds.
A number of approaches involving absorption features have been developed, including the use of almost complete absorption in the ultraviolet region of the spectrum to indicate that a diamond is not synthetic. The UV absorption is produced by the A center (two adjacent nitrogen atoms) and is rarely encountered in as-grown synthetic diamonds. The main form of nitrogen in synthetic diamonds is a single substitutional nitrogen atom that absorbs in both the ultraviolet and visible regions to produce yellow color. The combination of UV absorption and no strong yellow color is therefore restricted to natural diamond. However, treatment of nitrogen-containing synthetic diamonds is capable of generating A centers, but generally does not produce a colorless stone. This effect accounts for the careful color ranges often applied to instruments relying on UV absorption for screening. This also highlights one of the limitations of absorption spectroscopy: When smaller stones are tested, the amount of absorption decreases and the technique becomes less reliable. In recent years we have seen a shift to smaller sizes (below 0.01 ct) in the synthetic diamonds being offered for sale to the jewelry market, and screening techniques have had to evolve to address this situation and the limitations of absorption-based approaches.
Testing melee-sized diamonds, as well as introducing technical challenges around the measurement technique, has also led to the introduction of greater automation. In 2014 the De Beers Group introduced the first automated melee screening instrument (AMS1), which combined the measurement technique from DiamondSure with automated feeding and dispensing of stones in the range of 0.20 to 0.01 ct. While this instrument was well received and effectively addressed concerns around synthetic melee-sized stones in the trade at the time, there soon came calls for improvements—a faster instrument capable of measuring smaller stones, no restrictions on cut, and a lower referral rate for natural diamonds. These requirements proved impossible to meet with the limitations imposed by absorption measurements, and a new technique based on time-resolved spectroscopy was developed. This resulted in the AMS2 instrument, launched in March 2017. The AMS2 processes stones at a speed of one stone per second, 10 times faster than the AMS1. It measures round brilliants down to 0.003 ct (0.9 mm diameter) and can be used on other cuts for stones of 0.01 ct and above. The measurement technique itself has been incorporated into the SYNTHdetect (figure 1, left), an instrument launched in September 2017 that allows manual observation of the time-resolved emission. Besides providing the same testing capability as AMS2 (figure 1, right) for loose stones, various holders allow testing of mounted stones in a wide range of configurations. The benefit of this approach is that stones tested loose using AMS2 will generate a broadly consistent result when mounted on SYNTHdetect.

Figure 1. The De Beers Group instruments SYNTHdetect (left) and AMS2 (right) provide screening capability for melee-size diamonds as small as 0.3 points. Photo courtesy of Danny Bowler © De Beers Group.
Changes in growth processes for synthetic diamonds have also led to the gradual introduction of new characteristics. High-pressure, high-temperature (HPHT) synthetics have tended to be fairly consistent in their growth-related luminescence patterns, while significant variations in the features associated with chemical vapor deposition (CVD) synthetics have been observed. These continue to be well documented and have led to the gradual evolution of the DiamondView instrument and the way in which it is used.
Post-growth treatment of synthetic diamonds can be applied for a number of reasons: improvement in the color, modification of the atomic defects to make the stones look more like a natural diamond, and removal of a characteristic that could be used to identify a synthetic diamond. The motivation for the latter two treatments can only be described as fraudulent. The challenge in developing detection instruments and techniques is to ensure that they are as robust as possible in the face of such challenges. Treatment techniques will rarely have any effect on the growth patterns associated with synthetic diamonds, and it is therefore very difficult to treat synthetics in a way that would make them undetectable using the DiamondView. Screening instruments tend to be based on a single technique, and it is important that the approach adopted not be vulnerable to simpler forms of treatment. This has been of primary concern to the De Beers Group in the development of our own screening instruments. It has also been necessary in certain cases to withhold detailed information about detection techniques where disclosure of this would lead to undermining of the detection technique itself.
The De Beers Group continues to invest heavily in growth and treatment research in order to develop the next generation of instruments and techniques that will assist the trade in maintaining detection capability to support consumer confidence. The Group is uniquely placed in the industry to address these challenges due to its collaboration with Element Six (world leaders in synthesis of diamond for industrial and technical applications) and its in-depth knowledge of the properties of natural diamonds with known provenance from its own mines.
Diamond at the Diffraction Limit: Optical Characterization of Synthetic Diamond
Phil L. Diggle1,2, Ulrika F.S. D’Haenens-Johansson3, Wuyi Wang3, and Mark E. Newton1,2
1Department of Physics, University of Warwick, Coventry, United Kingdom
2EPSRC Centre for Doctoral Training in Diamond Science and Technology, Warwick, United Kingdom
3GIA, New York
Diamond, known for its splendor in exquisite jewelry, has been synthesized since the 1950s. In the last six decades, the perfection of laboratory-grown single-crystal diamond has vastly improved through the research and development of two main synthesis techniques. One replicates Earth’s natural process, where the diamond is grown in the laboratory under conditions of diamond stability at high temperature and high pressure (HPHT). The other technique relies on the dissociation of methane (or other carbon-containing source gas) and hydrogen and the subsequent deposition of diamond at low pressures from the gaseous phase in a process known as chemical vapor deposition (CVD). In the latter case, diamond is not the stable form of carbon, but the kinetics in the CVD process are such that diamond wins out. Large gem-quality synthetic diamonds are now possible, and a 6 ct CVD (2018) and a 15.32 ct HPHT (2018) have been reported.
It is of course possible to differentiate laboratory-grown from natural diamond based on how extended and point defects are incorporated into the crystal. Furthermore, treated diamond can be identified utilizing knowledge of how defects are produced and how they migrate and aggregate in both natural and synthetic diamond samples. Room-temperature confocal photoluminescence microscopy can be used to image the emission of light from defects in diamond with a spatial resolution limited only by the diffraction limit; a lateral spatial resolution approaching 300 nm is routinely achieved (figure 1). It is possible with this tool to identify point defects with concentrations less than 1 part per trillion (1011 cm–3).

Figure 1. Left: DiamondView fluorescence imaging shows dislocation networks in a natural type IIa diamond. Right: A room-temperature confocal photoluminescence image taken with 488 nm excitation shows H3 defects following a dislocation network pattern within the diamond. Some of the fluorescent spots are single H3 centers.
This talk will outline the experimental setup, how this tool has been used to identify the decoration of dislocations with point defects in CVD lab-grown diamond, and how different mechanisms for defect incorporation operate at growth sector boundaries in HPHT synthetic diamond.
Fluorescence in Diamond: New Insights
Ans Anthonis, John Chapman, Stefan Smans, Marleen Bouman, and Katrien De Corte
HRD Antwerp, Belgium
The effect of fluorescence on the appearance of diamonds has been a subject of debate for many years (Moses et al., 1997). In the trade, fluorescence is generally perceived as an undesirable characteristic. Nearly 80% of diamonds graded at HRD Antwerp receive a “nil” fluorescence grade, while the remainder are graded as “slight,” “medium,” and “strong,” their value decreasing with level of fluorescence.
To understand how fluorescence might change diamond appearance, a selection of 160 round brilliant-cut diamonds were investigated in detail. This study focused on the effect of fluorescence on diamond color. The aim was to determine under what lighting conditions the color of a diamond could change and the magnitude of that effect. We also investigated a smaller selection of diamonds with multiple spectroscopic absorption techniques to study the origin of their fluorescence.
The lighting arrangement we used combined the UV from light-emitting diode (LED) lamps with the light from a daylight-equivalent (grading) fluorescent lamp that had its UV component filtered out. With controlled UV output and after calibrations, it was possible to simulate different illuminations, including outdoors, indoors near a window, office lighting, and grading environments. The grading environment provided the reference color. Diamonds were presented in both table-down and table-up orientations, with the degree of effect determined by visual comparison with nonfluorescent master stones. For each color, both experienced diamond graders and nonprofessionals examined the possible effect of fluorescence on color appearance.
It was found that the UV level in office lighting was insignificant and did not produce any observable effect even with “very strong” fluorescence. However, with daylight from either outdoors or indoors, near a window, the relative strength of UV was significant, sufficient to create a positive color change. For samples with a “very strong” fluorescence, the results are shown in figure 1. For each color, ranging from D to J, the color shift caused by exposure to different UV levels—represented by the different lighting conditions—is illustrated.

Figure 1. For samples with “very strong” fluorescence, the observed color in different lighting conditions (outdoor, indoor, and office) is shown. These samples were graded through the pavilion (table-down). Note that in an outdoor environment, J colors can appear as D colors.
REFERENCE
Moses T.M., Reinitz I.M., Johnson M.L., King J.M., Shigley J.E. (1997) A contribution to understanding the effect of blue fluorescence on the appearance of diamonds. G&G, Vol. 33, No. 4, pp. 244–259, http://dx.doi.org/10.5741/GEMS.33.4.244
Fluorescence, Phosphorescence, Thermoluminescence, and Charge Transfer in Synthetic Diamond
Jiahui (Gloria) Zhao1,2, B.G. Breeze1,3, B.L. Green1, Phil L. Diggle1,2, and Mark E. Newton1,2
1Department of Physics, University of Warwick, Coventry, United Kingdom
2EPSRC Centre for Doctoral Training in Diamond Science and Technology, Warwick, United Kingdom
3Spectroscopy Research Technology Platform, University of Warwick, Coventry, United Kingdom
Photoluminescence (PL) and phosphorescence underpin many of the discrimination techniques used to separate natural from synthetic diamond. PL is at the heart of many new quantum technologies based on color centers in lab-grown diamonds. In HPHT synthetic diamond, the phosphorescence observed is explained in terms of donor-acceptor pair recombination. The thermal activation of electrons to neutral boron acceptors shows that boron plays a key role in the phosphorescence process. However, there are a number of things we struggle to explain. For example, the phosphorescence peak positions are not fully explained, and there is no conclusive link between the emission and charge transfer involving the substitutional nitrogen donor.
Secondly, the origin of the phosphorescence observed in some synthetic diamond samples grown by the CVD process is unclear. Although we now have evidence for unintentional boron impurity incorporation at stop-start growth boundaries in some CVD synthetic samples, it is possible that some of the observed phosphorescence does not involve boron impurities.
In this paper we report on the results of combined fluorescence, phosphorescence, thermoluminescence, and quantitative charge transfer investigations undertaken on both HPHT and CVD synthetic diamond, with the objective of identifying which defects are involved in the fluorescence and phosphorescence processes.
LPHT-Treated Pink CVD Synthetic Diamond
Hiroshi Kitawaki, Kentaro Emori, Mio Hisanaga, Masahiro Yamamoto, and Makoto Okano
Central Gem Laboratory, Tokyo
Pink diamond is extremely popular among fancy-color diamonds, which has prompted numerous attempts to produce pink diamond artificially. Pink CVD synthetic diamonds appeared on the gem market around 2010. Their color was produced by a multistep process combining post-growth HPHT treatment to remove the brown hue and subsequent electron irradiation, followed by low-temperature annealing. Pink CVD synthetic diamonds treated only with low pressure and high temperature (LPHT), without additional post-growth irradiation, have also been reported but are rarely seen on the market.
Recently, a loose pink stone (figure 1) was submitted to the Central Gem Laboratory in Tokyo for grading purposes. Our examination revealed that this 0.192 ct brilliant-cut marquise was a CVD synthetic diamond that had been LPHT treated.

Figure 1. LPHT-treated brownish pink CVD synthetic diamond weighing 0.192 ct. Photo by Hiroshi Kitawaki.
Visually, this diamond could not be distinguished from natural diamonds with similar color. However, three characteristics of CVD origin were detected:

C-H related absorption peaks between 3200 and 2800 cm–1, located with infrared spectroscopy
A luminescence peak at 737 nm, detected with photoluminescence (PL) spectroscopy
A trace of lamellar pattern seen in the DiamondView

However, irradiation-related peaks such as at 1450 cm–1 (H1a), 741.1 nm (GR1), 594.3 nm, or 393.5 nm (ND1) that are seen in the pink CVD diamonds treated with common multi-step processes were not detected.
The presence of four peaks at 3123, 2901, 2870, and 2812 cm–1 between 3200 and 2800 cm–1 suggests this stone was LPHT treated; the following observations indicate that it was not HPHT treated:

The 3123 cm–1 peak presumably derived from NVH0 disappears after a normal HPHT treatment.
The 2901, 2870, and 2812 cm–1 peaks are known to shift toward higher wavenumbers as the annealing temperature rises. Our own HPHT treatment experiments on CVD-grown diamonds proved that the 2902 and 2871 cm–1 peaks detected after 1600°C annealing shifted to 2907 and 2873 cm–1 after 2300°C annealing. The peak shift of 2901, 2870, and 2812 cm–1 is also related to the pressure during the annealing, as these peaks shifted to 2902, 2871, and 2819 cm–1 at the higher pressure of 7 GPa compared to 2900, 2868, and 2813 cm–1 at the ambient pressure under the same annealing temperature of 1600°C.
Absorption peaks at 7917 and 7804 cm–1 in the infrared region and at 667 and 684 nm in the visible range were also detected, which coincide with the features seen in LPHT-treated stones. From the combination of the intensity ratios of optical centers such as H3 and NV centers that were detected with PL measurement, this sample is presumed to have been treated with LPHT annealing at about 1500–1700°C as a post-growth process.

In recent years, CVD synthetic diamonds have been produced in a wider range of colors due to progress in the crystal growth techniques and post-growth treatments. Although HPHT treatment has been employed mainly to improve the color in a diamond, LPHT annealing may become widespread as the technique is further developed. Gemologists need to have deep knowledge about the optical defects in such LPHT-treated specimens.
Recent Developments in Detection and Gemology in China, Particularly for Chinese Synthetic Diamonds
Jie Ke, Taijin Lu (presenter), Yan Lan, Zhonghua Song, Shi Tang, Jian Zhang, and Hua Chen
National Gemstone Testing Center (NGTC), Beijing
China is the world’s largest producer of HPHT-grown industrial diamonds. Its 2016 production of about 20 billion carats accounted for 98% of the global supply. Since the beginning of 2015, melee-sized colorless HPHT synthetic diamonds have been tested at the National Gemstone Testing Center’s (NGTC) Shenzhen and Beijing laboratories in parcels submitted by different clients, which means that colorless HPHT synthetic diamonds have entered the Chinese jewelry market and may be mistaken for natural diamonds.
CVD synthesis technology has grown rapidly in recent years. Large colorless and colored (blue, pink) CVD-grown diamonds have been entering the market, and a few have been fraudulently sold as natural diamonds.
China has independently developed gem-grade HPHT synthetic diamond production technology since 2002, and can grow gem-grade type Ib, IIa, and IIb and high-nitrogen-content synthetic diamonds in volume, depending on market needs. Gem-grade type Ib, IIa, and IIb HPHT synthetic diamonds have been grown using the temperature gradient method, under a cubic press at high pressure (e.g., 5.4 GPa) and high temperature (1300–1600°C). Driven by a specific temperature gradient, the carbon source from high-purity graphite (>99.9%) located at the high-temperature zone can diffuse into the seed crystals in the cubic press, resulting in the crystallization of synthetic diamonds. Chinese production of melee-sized colorless to near-colorless HPHT synthetic diamonds accounts for about 90% of the global output.
Gem-grade type IIa and IIb CVD synthetic diamonds are grown using the microwave plasma chemical vapor deposition (MPCVD) and direct current (DC) arc plasma methods. Faceted colorless CVD diamonds can be grown in sizes up to 6 ct by at least two Chinese companies (table 1).

After testing and analyzing thousands of natural and synthetic diamonds collected directly from the Chinese companies, NGTC independently developed the GV5000, PL5000, DS5000, and ADD6000 instruments for rapidly screening and identifying the diamonds based on the gemological characteristics obtained.
Besides HPHT and CVD synthetic diamonds, a thickly layered hybrid diamond consisting of both natural and CVD material was identified at the NGTC Beijing laboratory (figure 1). The identification features and properties of regrown CVD synthetic diamonds using natural type Ia diamond crystals as seeds will be reported.

Figure 1. DiamondView fluorescence image of the hybrid natural and CVD-grown diamond. Photo by Shi Tang.
The current status and features of colored stones examined at NGTC laboratories, including several cases studies, will be discussed.
Summary of CVD Lab-Grown Diamonds Seen at the GIA Laboratory
Sally Eaton-Magaña
GIA, Carlsbad, California
While chemical vapor deposition (CVD) diamond growth technology has progressed significantly in recent years, with improvements in crystal size and quality, the use of these goods in the jewelry trade is still limited. Not all CVD-grown gem diamonds are submitted to GIA for grading reports, and they only account for about 0.01% of GIA’s annual diamond intake (both D–Z equivalents and fancy color; Eaton-Magaña and Shigley, 2016). The CVD process involves diamond growth at moderate temperatures (700–1300°C) but very low pressures of less than 1 atmosphere in a vacuum chamber (e.g., Angus and Hayman, 1988; Nad et al., 2015). This presentation summarizes the quality factors and other characteristics of the CVD-grown material submitted to GIA (e.g., figure 1) and discusses new research and products.

Figure 1. Spectra and fluorescence images of all D–N equivalent CVD-grown diamonds seen at GIA from 2007 to 2018 were analyzed. The vast majority (74%) show features consistent with post-growth HPHT treatment. The percentage of as-grown CVD products increases as the equivalent color progresses from the colorless range (D–F) to near-colorless (G–J) to faint brown (K–N).
Today the CVD process is used to produce high-color (as well as fancy-color) and high-clarity type II diamonds up to several carats in size. The majority of the CVD material seen at GIA consists of near-colorless (G–N equivalent) with colorless (D–F equivalent) and various “pink” hues. Additionally, CVD material is constantly setting new size milestones, with the announcement of an approximately 6 ct round brilliant earlier this year (Davis, 2018). However, the attainable sizes among CVD products are dwarfed by those from the HPHT process, with 15.32 ct as the current record for a faceted gem (Ardon and Eaton-Magaña, 2018).
One particular challenge for gemologists (albeit very rarely encountered) comes from the lab-grown/natural hybrids (figure 2) that have been submitted to and documented by gemological laboratories (e.g., Moe et al., 2017; Tang et al., 2018). In these specimens, the grower places a natural diamond into the CVD reactor as the seed plate, with both components retained in the faceted gem. If the manufacturer is using a colorless natural type Ia diamond as a seed plate for near-colorless CVD growth, the hybrid cannot undergo any post-growth HPHT treatment, as this would radically alter the natural seed by turning the natural diamond yellow. If the manufacturer is creating a CVD overgrowth layer on a faceted natural diamond, the intent is to either add weight to a diamond that may be near a weight boundary or to achieve a color change, typically to blue. These hybrid products also make it more difficult to infer a diamond’s history based solely on its diamond type.

Figure 2. This 0.33 ct CVD-grown/natural diamond composite with a color equivalent to Fancy blue was previously described (Moe et al., 2017). DiamondView illumination clearly shows the interface between the lab-grown and natural components.
The CVD process has also created some unique gems that have not been duplicated among natural, treated, or HPHT-grown diamonds. These include CVD-grown diamonds with a high concentration of silicon impurities, which create a pink to blue color shift. In those samples, a temporary effect was activated by UV exposure, which precipitated a charge transfer between negative and neutral silicon-vacancy centers (D’Haenens-Johansson et al., 2015).
Also recently seen are type IIb CVD goods. Some that were submitted by clients had a low boron concentration (3 ppb, with G-equivalent color and 1.05 carat weight). Meanwhile, some research samples produced by a manufacturer in China and fashioned as flat plates had dark bluish coloration and very high boron concentration (2500 ppb and higher). Also among that suite of flat-plate CVD samples was one with a black color caused by extremely high amounts of nitrogen-vacancy centers.
Although new CVD products are continually being manufactured and introduced to the trade, the laboratory-grown diamonds examined to date by GIA can be readily identified.
REFERENCES
Angus J.C., Hayman C.C. (1988) Low-pressure, metastable growth of diamond and diamondlike phases. Science, Vol. 241, No. 4868, pp. 913–921.
Ardon T., Eaton-Magaña S.C. (2018) Lab Notes: 15 carat HPHT synthetic diamond. G&G, Vol. 54, No. 2, pp. 217–218.
Davis A. (2018) Washington, D.C., company grows 6-carat diamond. National Jeweler, Jan. 31, https://www.nationaljeweler.com/diamonds-gems/supply/6267-washington-d-c-company-grows-6-carat-diamond
D’Haenens-Johansson U.F.S., Ardon T., Wang W. (2015) CVD synthetic gem diamonds with high silicon-vacancy concentrations. Conference on New Diamond and Nano Carbons, May 2015, Shizuoka, Japan.
Eaton-Magaña S.C., Shigley J.E. (2016) Observations on CVD-grown synthetic diamonds: A review. G&G, Vol. 52, No. 3, pp. 222–245, http://dx.doi.org/10.5741/GEMS.52.3.222
Moe K.S., Johnson P., D’Haenens-Johansson U.F.S., Wang W. (2017) Lab Notes: A CVD synthetic diamond overgrowth on a natural diamond. G&G, Vol. 53, No. 2, pp. 237–239.
Nad S., Gu Y., Asmussen J. (2015) Growth strategies for large and high quality single crystal diamond substrates. Diamond and Related Materials, Vol. 60, pp. 26–34, http://dx.doi.org/10.1016/j.diamond.2015.09.018
Tang S., Su J., Lu T., Ma Y., Ke J., Song Z., Zhang J., Liu H. (2018) A thick overgrowth of CVD synthetic diamond on a natural diamond. Journal of Gemmology, Vol. 36, No. 2. pp. 237–239. @topic:4


Publish Year: 2018 Title: Diamond Geology Abstract: Modern Advances in the Understanding of Diamond Formation
D. Graham Pearson
University of Alberta, Edmonton, Canada
For the past 50 years, the majority of diamond research has focused on diamonds derived from the lithospheric mantle root underpinning ancient continents. While lithospheric diamonds are currently thought to form the mainstay of the world’s economic production, the continental mantle lithosphere reservoir comprises only ~2.5% of the total volume of Earth. Earth’s upper mantle and transition zone, extending from beneath the lithosphere to a depth of 670 km, occupy a volume approximately 10 times larger.
Diamonds from these deeper parts of the earth—“superdeep diamonds”—are more abundant than previously thought. They appear to dominate the high-value large diamond population that comes to market. Recent measurements of the carbon and nitrogen isotope composition of superdeep diamonds from Brazil and southern Africa, using in situ ion probe techniques, show that they document the deep recycling of volatile elements (C, N, O) from the surface of the earth to great depths, at least as deep as the uppermost lower mantle. The recycled crust signatures in these superdeep diamonds suggest their formation in regions of subducting oceanic plates, either in the convecting upper mantle or the transition zone plus lower mantle. It is likely that the deep subduction processes involved in forming these diamonds also transport surficial hydrogen into the deep mantle. This notion is supported by the observation of a high-pressure olivine polymorph—ringwoodite—with close to saturation levels of water. Hence, superdeep diamonds document a newly recognized, voluminous “diamond factory” in the deep earth, likely producing diamonds right up to the present day. Such diamonds also provide uniquely powerful views of how crustal material is recycled into the deep earth to replenish the mantle’s inventory of volatile elements.
The increasing recognition of superdeep diamonds in terms of their contribution to the diamond economy opens new horizons in diamond exploration. Models are heavily influenced by the search for diamonds associated with highly depleted peridotite (dunites and harzburgites). Such harzburgitic diamonds were formed in the Archean eon (>2.5 Ga) within lithospheric mantle of similar age. It is currently unclear what the association is between these ancient lithospheric diamonds and large, high-value diamonds, but it is likely a weak one. In contrast, the strong association between superdeep diamonds and these larger stones opens up a new paradigm because the available age constraints for superdeep diamonds indicate that they are much younger than the ancient lithospheric diamonds. Their younger age means that superdeep diamonds may be formed in non-Archean mantle, or mantle that has been strongly overprinted by post-Archean events that would otherwise be deemed unfavorable for the preservation of ancient lithospheric diamonds.
An additional factor in the search for new diamond deposits is the increasing recognition that major diamond deposits can form in lithospheric mantle that is younger than—or experienced major thermal disruption since—the canonical 2.5 billion years usually thought to be most favorable for diamond production.
This talk will explore these new dimensions in terms of the potential for discovering new diamond sources in “unconventional” settings.
Diamond Precipitation from High-Density CHO Fluids
Thomas Stachel1, Robert W. Luth1, and Oded Navon2
1University of Alberta, Edmonton, Canada
2Hebrew University, Jerusalem
Through research on inclusions in diamonds over the past 50 years, a detailed picture has emerged of the mineralogical and chemical composition of diamond substrates in Earth’s mantle and of the pressure-temperature conditions during diamond formation. The exact diamond-forming processes, however, are still a subject of debate.
One approach to constrain diamond-forming processes is through model calculations that aim to obtain the speciation and the carbon content of carbon-hydrogen-oxygen (CHO) fluids at particular O/(O+H) ratios and pressure-temperature conditions (using GFluid of Zhang and Duan, 2010, or other thermodynamic models of fluids). The predictions of such model calculations can then be tested against carbon and nitrogen stable isotopes and nitrogen content fractionation models, based on in situ analyses across homogenously grown diamond growth layers. Based on this approach, Luth and Stachel (2014) proposed that diamond precipitation occurs predominantly from cooling or ascending CHO fluids, composed of water with minor amounts of CO2 and CH4 (which in response to decreasing temperature may react to form diamond: CO2+ CH4 → 2C + 2H2O).
The second approach focuses on constraining the diamond-forming medium by studying submicrometer fluid inclusions in fibrous-clouded and, more recently, gem diamonds. Such studies established the presence of four compositional end members of inclusions: hydrous-saline, hydrous-silicic, high-Mg carbonatitic, and low-Mg carbonatitic (e.g., Navon et al., 1988; Weiss et al., 2009). Although these fluid inclusions only depict the state of the diamond-forming medium after formation, they nevertheless provide unique insights into the major and trace-element composition of such fluids that otherwise could not be obtained.
The apparent dichotomy between the two approaches—models for pure CHO fluids and actual observation of impure fluids (so-called high-density fluids) in clouded and fibrous diamonds—relates to the observation that in high-pressure and high-temperature experiments close to the melting temperature of mantle rocks, hydrous fluids contain 10–50% dissolved solid components (e.g., Kessel et al., 2015). Although at this stage the impurity content in natural CHO fluids cannot be included in numerical models, the findings for clouded and fibrous diamonds are not in conflict with the isochemical diamond precipitation model. Specifically, the fact that observed high-density inclusions are often carbonate bearing is not in conflict with the relatively reducing redox conditions associated with the O/(O+H) ratios of modeled diamond-forming CHO fluids. The model for the minimum redox stability of carbonate-bearing melts of Stagno and Frost (2010) permits fluid carbonate contents of up to about 30% at such redox conditions.

Figure 1. This illustration depicts the isochemical precipitation of diamond in Earth’s lithospheric mantle. Top: Intrusion of magma (ΔT to peridotitic wall rock is about +200°C) leads to release of hot CHO fluids from the crystallizing melt. As it infiltrates the peridotitic wall rock, the cooling fluid isochemically precipitates diamond. Bottom: After crystallization of the melt is completed, the intrusion is surrounded by an aureole of diamond, with temperature, volume, fluid content, and redox state of the melt all influencing the amount of diamond precipitated.
Although additional data need to be obtained to build a thermodynamic model for CHO fluids with dissolved silicates and to better characterize the major and trace-element composition of high-density CHO fluids in equilibrium with typical diamond substrates (the rock types peridotite and eclogite), we already see sufficient evidence to suggest that the two approaches described above are converging to a unified model of isochemical diamond precipitation from cooling or ascending high-density CHO fluids.
REFERENCES
Kessel R., Fumagalli P., Pettke T. (2015) The behaviour of incompatible elements during hydrous melting of metasomatized peridotite at 4–6 GPa and 1000°C–1200°C. Lithos, Vol. 236-237, pp. 141–155, https://doi.org/10.1016/j.lithos.2015.08.016

Luth R.W., Stachel T. (2014) The buffering capacity of lithospheric mantle: implications for diamond formation. Contributions to Mineralogy and Petrology, Vol. 168, No. 5, pp. 1–12, https://doi.org/10.1007/s00410-014-1083-6

Navon O., Hutcheon I.D., Rossman G.R., Wasserburg G.J. (1988) Mantle-derived fluids in diamond micro-inclusions. Nature, Vol. 335, No. 6193, pp. 784–789, https://doi.org/10.1038/335784a0

Stagno V., Frost D.J. (2010) Carbon speciation in the asthenosphere: Experimental measurements of the redox conditions at which carbonate-bearing melts coexist with graphite or diamond in peridotite assemblages. Earth and Planetary Science Letters, Vol. 300, No. 1-2, pp. 72–84, https://doi.org/10.1016/j.epsl.2010.09.038

Weiss Y., Kessel R., Griffin W.L., Kiflawi I., Klein-BenDavid, O., Bell D.R., Harris J.W., Navon O. (2009) A new model for the evolution of diamond-forming fluids: Evidence from microinclusion-bearing diamonds from Kankan, Guinea. Lithos, Vol. 112 (Supplement 2), pp. 660–674, https://doi.org/10.1016/j.lithos.2009.05.038

Zhang C., Duan Z.H. (2010) GFluid: An Excel spreadsheet for investigating C-O-H fluid composition under high temperatures and pressures. Computers & Geosciences, Vol. 36, No. 4, pp. 569–572, https://doi.org/10.1016/j.cageo.2009.05.008
How to Obtain and Interpret Diamond Ages
Steven B. Shirey1 and D. Graham Pearson2
1Carnegie Institution for Science, Washington, DC
2University of Alberta, Edmonton, Canada
Diamond ages are obtained from radiogenic isotopic analysis (Rb-Sr, Sm-Nd, Re-Os, and Ar-Ar) of mineral inclusions (garnet, pyroxene, and sulfide). As diamonds are xenocrysts that cannot be dated directly, the ages obtained on mineral inclusions provide a unique set of interpretive challenges to assure accuracy and account for preexisting history. A primary source of geological/mineralogical uncertainty on diamond ages is any process affecting protogenetic mineral inclusions before encapsulation in the diamond, especially if it occurred long before diamond formation. In practical application, the isotopic systems discussed above also carry with them inherent systemic uncertainties. Isotopic equilibrium is the essential condition required for the generation of a statistically robust isochron. Thus, isochron ages from multiple diamonds will record a valid and accurate age when the diamond-forming fluid promotes a large degree of isotopic equilibrium across grain scales, even for preexisting (“protogenetic”) minerals. This clearly can and does occur. Furthermore, it can be analytically tested for, and has multiple analogues in the field of dating metamorphic rocks. In cases where an age might be suspect, an age will be valid if its regression uncertainties can encompass a known and plausible geological event (especially one for which an association exists between that event and the source of diamond-forming fluids) and petrogenetic links can be established between inclusions on the isochron.

Figure 1. Left: Re-Os isotopic compositions for 10 sulfides from three Zimmi diamonds all fall along 650 Ma age arrays. Each diamond had multiple sulfides that lay on arrays of identical age, giving unequivocal evidence for the age and showing that these diamonds formed in the same episode of diamond formation. Right: Plane polarized light image of a typical sulfide inclusion in a polished Zimmi diamond plate. Note that this diamond only contains one inclusion, whereas analyses of three to four inclusions per diamond are shown in the plot on the left. From Smit et al. (2016), used with permission.

Diamonds can be dated in six basic ways:

model ages
radiogenic daughter Os ages (common-Os-free)
single-diamond mineral isochrons
core to rim ages
multiple single-diamond isochron/array ages
composite isochron/array ages

Model ages (1) are produced by the intersection between the evolution line for the inclusion and a reference reservoir such as the mantle. The most accurate single-diamond age is determined on a diamond with multiple inclusions (3). In this case an internal isochron can be obtained that not only establishes equilibrium among the multiple grains but also unequivocally dates the time of diamond growth. With extreme luck in obtaining the right diamond, concentric diamond growth zones visible in UV fluorescence or cathodoluminescence can sometimes be shown to constrain inclusions to occur in the core of the diamond and in the exterior at the rim. These single grains can be extracted to give a minimum growth time (4) for the diamond. In optimal situations, multiple inclusions are present within single growth zones, in single diamonds, allowing internal isochrons to be constructed for individual growth zones in single diamonds. If enough diamonds with inclusions can be obtained for study, valid ages for diamond populations can be obtained on multiple single-diamond ages that agree (5) or on composited, mineralogically similar inclusions to give an average age (6).
REFERENCE
Smit K.V., Shirey S.B., Wang W. (2016) Type Ib diamond formation and preservation in the West African lithospheric mantle: Re–Os age constraints from sulphide inclusions in Zimmi diamonds. Precambrian Research, Vol. 286, pp. 152–166, http://dx.doi.org/10.1016/j.precamres.2016.09.022
The Lesedi La Rona and the Constellation—The Puzzle of the Large Rough Diamonds from Karowe
Ulrika F.S. D’Haenens-Johansson
GIA, New York
In November 2015, Lucara Diamond’s operation at the Karowe mine in Botswana gained notoriety due to the extraction of a series of large colorless diamonds, including the 1,109 ct Lesedi La Rona and the 812 ct Constellation. The Lesedi La Rona marks the largest gem diamond recovered since the Cullinan (3,106 ct) in 1905. The Constellation, considered to be the seventh-largest recorded diamond, attained the highest price ever paid for a rough, selling for $63.1 million ($77,649 per carat). Additionally, three other significant colorless diamonds were recovered during the same period, weighing 374, 296, and 183 ct. Due to the similarity in their external characteristics—which include cleavage faces—as well as their extraction locations and dates, it was suspected that these stones might have originated from a larger rough that had broken. Lucara demonstrated that the 374 ct diamond and the Lesedi La Rona fit together, yet a large cleavage plane is still unaccounted for. GIA was able to study several rough and/or faceted pieces of these five diamonds using a range of spectroscopic and imaging techniques to gain insight into the presence and distribution of point defects in these diamonds.
Diamonds are commonly classified according to their nitrogen content measured by Fourier-transform infrared (FTIR) spectroscopy: Type I diamonds contain nitrogen in either isolated (Ib) or aggregated (IaAB) forms, while type II diamonds do not contain detectable nitrogen concentrations (IIa) but may contain boron (IIb). Analysis of faceted stones cut from the Lesedi La Rona indicates that the rough is a mixed-type diamond, containing both type IIa and pure type IaB regions. These types of diamonds, though exceedingly unusual, have been observed at GIA and reported by Delaunay and Fritsch (2017). The Constellation and the 374, 296, and 183 ct diamonds were determined to be type IaB, containing 20 ± 4 ppm B-aggregates (N4V), in agreement with the concentration for the type IaB pieces of the Lesedi La Rona. Pure type IaB diamonds such as these are actually quite rare, accounting for only 1.2% of a random suite of 5,060 large (>10 ct) D-to-Z diamonds submitted to GIA, whereas 24.6% were type II. Photoluminescence spectra further confirmed analogous defect content for the five large Karowe diamonds, with emissions from H4 (N4V20, 496 nm), H3 (NVN0, 503 nm), 505 nm, NV– (637 nm), and GR1 (V0, 741 nm) defects showing similar relative intensities and peak widths. Even for diamonds of the same type, parallel defect content and characteristics across such a variety of defects is unlikely for unrelated stones.
The external morphologies of the diamonds showed primary octahedral, resorbed, and fractured faces, with the Constellation and the 296 ct diamond featuring fractures containing metallic inclusions and secondary iron oxide staining. Deep UV fluorescence (< 230 nm) imaging elucidated the internal growth structures of the samples. For the Constellation and the 374, 296, and 183 ct diamonds, at least two growth zones with differing blue fluorescence intensities were observed within single pieces.
Combined with the spectroscopic data, these results provide compelling evidence that the Lesedi La Rona, the Constellation, and the 374, 296, and 183 ct diamonds from Karowe had comparable growth histories and likely originated from the same rough, with a combined weight of at least 2,774 ct.
REFERENCE
Delaunay A., Fritsch E. (2017) A zoned type IaB/IIa diamond of probable “superdeep” origin. Journal of Gemmology, Vol. 35, No. 5, pp. 397–399. @topic:8


Publish Year: - Title: Diamond Journey Abstract: Few people outside the gem industry realize the true nature of a gemstone’s journey from the mine to the counter of a store. Whether the gem is being offered to consumer’s at a traditional jewelry store’s counter, an internet shopping site, or a television broadcast the journey always involves a great deal of effort.  Tons of earth and countless hours of labor are needed to being a gem from mine to market. @topic:11


Publish Year: - Title: Diamond Description Abstract: However gem quality diamonds are fashioned from the original crystal shape they possess a combination of brightness, sparkle, fire, and sense of purity not matched by other gems. - Jeff Scovil, courtesy Barker & Co.

                      Diamond’s characteristic chemical composition and crystal structure make it a unique member of the mineral kingdom.

Diamond is the only gem made of a single element: It is typically about 99.95 percent carbon. The other 0.05 percent can include one or more trace elements, which are atoms that aren’t part of the diamond’s essential chemistry. Some trace elements can influence its color or crystal shape.

	Whether fashioned or rough, and no matter what their shape, all diamonds have the same chemical composition and internal crystal structure.
The way a mineral forms helps determine its identity. Diamond forms under high temperature and pressure conditions that exist only within a specific depth range (about 100 miles) beneath the earth’s surface. Diamond’s crystal structure is isometric, which means the carbon atoms are bonded in essentially the same way in all directions. Another mineral, graphite, also contains only carbon, but its formation process and crystal structure are very different. The result is that graphite is so soft that you can write with it, while diamond is so hard that you can only scratch it with another diamond.

	The most common shape for rough gem quality diamond is the octahedron, which looks like two pyramids back to back. Crystals that are almost perfect in shape and transparency are called glassies.
Without any one of these factors, diamond might be just another mineral. Fortunately, though, this special combination of chemical composition, crystal structure, and formation process gives diamonds the qualities that make them extraordinary.

	This diamond is a D color grade and has exceptional chemical purity. - Courtesy Lazare Kaplan Diamonds
On almost all modern birthstone lists, diamond is recognized today as the birthstone for April. Diamond is also the gem that marks the 60th and 75th wedding anniversaries.

	Diamond’s unique optical and physical properties give it the highest possible luster of any transparent gemstone. This is called adamantine luster after the Greek word Adamas meaning diamond-like. - Courtesy Chow Tai Fook Jewellery Co. @topic:10


Publish Year: 2018 Title: Diamond Geology Abstract: Figure 1. Left: The stone’s FTIR spectrum revealed that it is a type Ib-IaA diamond with nitrogen defects, “C” single nitrogen atoms and an “A” pair of nitrogen atoms. Right: DiamondView images show cuboctahedral growth structure containing a {100} sector with reddish orange fluorescence and a {111} sector with green fluorescence. Distinct fluorescence zoning following growth structure is caused by NV centers in {100} sectors and H3 defects in {111} sectors, which were created during the irradiation and annealing processes.
Type Ib–Dominant Mixed-Type Diamond with Cuboctahedral Growth Structure: A Rare Diamond Formation
Kyaw Soe Moe and Paul Johnson
GIA, New York
Type Ib–dominant mixed-type diamonds (Ib-IaA) can be formed by multiple growth events (Titkov et al., 2015; Smit et al., 2018). In this study, we report on a 0.41 ct Fancy Dark brown gemquality diamond that formed in a single growth event. It is a type Ib-IaA with a C defect (single-substitutional nitrogen atom) concentration up to 21 ppm. The Fourier-transform infrared (FTIR) peaks of the H1a and H1b defects (figure 1, left) suggest that this diamond was irradiated and annealed to achieve a Fancy color grade. The cuboctahedral structure can be observed in the DiamondView images (figure 1, right), which show reddish orange fluorescence in the {100} sector caused by NV centers and green fluorescence in the {111} sector caused by H3 defects. Irradiation treatment helps us to see the cuboctahedral structure. However, the presence of an amber center suggests that it did not undergo HPHT treatment.
Cuboctahedral growth structure can be usually observed in HPHT diamonds that are grown in a laboratory with a fast growth rate (i.e., less than one week per carat) under P-T conditions of 5–6 GPa and 1300–1500°C. A natural diamond that grows rapidly in a single growth event would also possess mixed cuboid and octahedral forms.
Time and temperature are critical in the aggregation of nitrogen atoms in diamond. Nitrogen atoms are initially incorporated as single atoms during diamond formation. Our sample was rich in C defects associated with A defects (a pair of nitrogen atoms). This suggests that the process of nitrogen aggregation was interrupted by the diamond’s ascent to shallower depths in the mantle at lower temperatures by rapid tectonic exhumation (Smit et al., 2018). The cuboctahedral growth structure of this diamond indicated that, prior to ascending to shallower depths of the mantle, it grew in a few days in the diamond stability field (i.e., 150–200 km in depth within the earth) in a single growth event.
REFERENCES
Smit K.V., D’Haenens-Johansson U.F.S., Howell D., Loudin L.C., Wang W. (2018) Deformation-related spectroscopic features in natural type Ib-IaA diamonds from Zimmi (West African craton). Mineralogy and Petrology, pp. 1–15, http://dx.doi.org/10.1007/s00710-018-0587-6

Titkov S.V., Shiryaev A.A., Zudina N.N., Zudin N.G., Solodova Y.P. (2015) Defects in cubic diamonds from the placers in the northeastern Siberian platform: Results of IR microspectrometry. Russian Geology and Geophysics, Vol. 56, No. 1-2, pp. 354–362, http://dx.doi.org/10.1016/j.rgg.2015.01.026
Evidence of Subducted Altered Oceanic Crust into Deep Mantle from Inclusions of Type IaB Diamonds
Tingting Gu1, John Valley2, Kouki Kitajima2, Michael Spicuzza2, John Fournelle2, Richard Stern3, Hiroaki Ohfuji4, and Wuyi Wang1
1GIA, New York
2Department of Geoscience, University of Wisconsin, Madison
3Canadian Centre for Isotopic Microanalysis (CCIM), Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton
4Geodynamics Research Center (GRC), Ehime University, Matsuyama, Japan
Nitrogen is one of the most common impurities in diamond, and its aggregation styles have been used as criteria for diamond classification. Pure type IaB diamonds (with 100% nitrogen in B aggregation) are rather rare among natural diamonds. The occurrence of the B center is generally associated with high temperature and a long residence time of the host diamond, which would potentially provide information on the earth’s deep interior. Seawater circulation is the unique process that shapes the surface of our planet and potentially has a profound effect on its interior due to slab subduction.
In about 50 type IaB diamonds with detectable micro-inclusions submitted to GIA for screening, we found that more than 70% of them contained a typical mineral assemblage from the sublithosphere. Jeffbenite (TAPP), majorite garnet, enstatite, and ferropericlase have been observed, which could be retrograde products of former bridgmanite. CaSiO3-walstromite with larnite and titanite is the dominant phase present in approximately 40% of all diamond samples. Direct evidence from oxygen isotope ratios measured by secondary ion mass spectrometry, or SIMS, (δ18OVSMOW in the range +10.7 to +12.5‰) of CaSiO3-walstromite with coexisting larnite and titanite that retrograde from CaSiO3-perovskite suggest that hydrothermally altered oceanic basalt can subduct to depths of >410 km in the transition zone. Incorporation of materials from subducted altered oceanic crust into the deep mantle produced diamond inclusions that have both lower mantle and subduction signatures. Ca(Si,Al)O3-perovskite was observed with a high concentration of rare earth elements (>5 wt.%) that could be enriched under P-T conditions in the lower mantle. Evidence from ringwoodite with a hydroxide bond, coexisting tuite and apatite, precipitates of an NH3 phase, and cohenite with trace amounts of Cl imply that the subducted brines can potentially introduce hydrous fluid to the bottom of the transition zone. In the diamonds with subducted materials, the increasing carbon isotope ratio from the core to the rim region detected by SIMS (δ13C from –5.5‰ to –4‰) suggests that an oxidized carbonate-dominated fluid was associated with recycling of the subducted hydrous material. The deep subduction played an important role in balancing redox exchange with the reduced lower mantle indicated by precipitated iron nanoparticles and coexisting hydrocarbons and carbonate phases.
Origin of Rare Fancy Yellow Diamonds from Zimmi (West Africa)
Karen V. Smit1, Ulrika F.S. D’Haenens-Johansson1, Daniel Howell2, Lorne C. Loudin1, and Wuyi Wang1
1GIA, New York
2Department of Geoscience, University of Padua, Italy, and Diamond Durability Laboratory, New York
Type Ib diamonds from Zimmi, Sierra Leone, have 500 My mantle residency times whose origin is best explained by rapid tectonic exhumation after continental collision to shallower depths in the mantle prior to kimberlite eruption (Smit et al., 2016). Here we present spectroscopic data for a new suite of Zimmi sulfide-bearing type Ib diamonds that allow us to evaluate the link between their rare Fancy yellow colors, the distribution of their spectroscopic features, and their unusual geological history. Cathodoluminesence (CL) imaging revealed irregular patterns with abundant deformation lamellae, associated with the diamonds’ tectonic exhumation (Smit et al., 2018). Vacancies formed during deformation were subsequently naturally annealed to form vacancy clusters, NV0/− centers, and H3 (NVN0). The brownish yellow to greenish yellow colors observed in Zimmi type Ib diamonds result from visible absorption by a combination of isolated nitrogen and deformation-related vacancy clusters (Smit et al., 2018). Color-forming centers and other spectroscopic features can all be attributed to the unique geological history of Zimmi type Ib diamonds and their rapid exhumation after formation.
REFERENCES
Smit K.V., Shirey S.B., Wang W. (2016) Type Ib diamond formation and preservation in the West African lithospheric mantle: Re-Os age constraints from sulphide inclusions in Zimmi diamonds. Precambrian Research, Vol. 286, pp. 152–166, http://dx.doi.org/10.1016/j.precamres.2016.09.022

Smit K.V., D’Haenens-Johansson U.F.S., Howell D., Loudin L.C., Wang W. (2018) Deformation-related spectroscopic features in natural type Ib-IaA diamonds from Zimmi (West African craton). Mineralogy and Petrology, pp. 1–15, http://dx.doi.org/10.1007/s00710-018-0587-6 @topic:4