DIAMOND Natural Colorless Type Iab Diamond with Silicon-Vacancy

Editors Thomas M. Moses | Shane F. McClure

DIAMOND logical and spectroscopic features con- Natural Colorless Type IaB firmed the diamond’s natural origin, – Diamond with Silicon-Vacancy despite the occurrence of [Si-V] emis- Defect Center sions. No treatment was detected. Examination of this stone indicated The silicon-vacancy defect, or [Si-V]–, that the [Si-V]– defect can occur, albeit is one of the most important features rarely, in multiple types of natural dia- in identifying CVD synthetic diamonds. Therefore, all properties should monds. It can be effectively detected be carefully examined in reaching a using laser photoluminescence tech- conclusion when [Si-V]– is present. nology to reveal sharp doublet emissions at 736.6 and 736.9 nm. This Carmen “Wai Kar” Lo defect is extremely rare in natural diamonds (C.M. Breeding and W. Wang, “Occurrence of the Si-V defect center Figure 1. Emissions from the Screening of Small Yellow Melee for in natural colorless gem diamonds,” silicon-vacancy defect at 736.6 and Treatment and Synthetics Diamond and Related Materials, Vol. 736.9 nm were detected in this Diamond treatment and synthesis 17, No. 7–10, pp. 1335–1344) and has 0.40 ct type IaB natural diamond. have undergone significant develop- been detected in very few natural type ments in the last decade. During this IIa and IaAB diamonds over the past showed blue fluorescence with natural time, the trade has grown increasingly several years. diamond growth patterns. These gemo- concerned about the mixing of treated Recently, a 0.40 ct round brilliant diamond with D color and VS2 clarity (figure 1) was submitted to the Hong Figure 2. The emission peaks at 736.6 and 736.9 nm from the [Si-V]– defect Kong laboratory for grading service. It are shown in the type IaB diamond’s photoluminescence spectrum. Iden- was identified as a pure type IaB natu- tical peak positions are detected in CVD synthetic diamonds. ral diamond. Infrared absorption spectroscopy showed low concentrations PHOTOLUMINESCENCE SPECTRA –1 of the hydrogen peak (3107 cm ) and 736.9 N impurities in the B aggregates. Photo luminescence spectra at liquid- 736.6 nitrogen temperature with 514 nm laser excitation revealed [Si-V]– doublet emissions at 736.6 and 736.9 nm (figure 2), while 457 nm laser excitation Natural type IaB diamond revealed the H3 (503.2 nm) emission. DiamondView fluorescence images INTENSITY

Editors’ note: All items were written by staff members of GIA laboratories. CVD synthetic type IIa diamond

GEMS & GEMOLOGY, Vol. 50, No. 4, pp. 293–301.

LAB NOTES GEMS & GEMOLOGY WINTER 2014 293 Figure 3. This group of 359 in- tensely colored round yellow diamonds (0.02–0.03 ct) was screened by GIA’s New York laboratory. Among these, the majority were natural (left), 14 were HPHT synthetics (middle), and one was HPHT-treated natural diamond (right). They all displayed uni- form appearance and could not be distinguished visually. and/or synthetic diamonds with natu- and treated diamonds found in this when determining diamond origin. ral melee-sized goods. Because it is parcel, we analyzed an additional par- This study indicates that melee di- often not feasible to test every small cel containing 525 samples, with amonds in the marketplace are being diamond in a parcel, many of these similar results. One of these was contaminated by synthetic and treated products could be traded without being HPHT-processed, while 10 displayed diamonds. Screening analysis by gem tested individually by a gem lab. GIA’s the spectral, microscopic, and fluo- labs is essential to ensuring the correct New York laboratory recently tested rescence characteristics typical of identification. An efficient and reli- two large groups of melee yellow dia- HPHT synthetics; we concluded that able screening can be performed using monds submitted for screening of the remaining 514 were natural and infrared absorption spectroscopy, Dia- treatments and synthetics. The results untreated. Typical DiamondView mondView fluorescence imagery, and will likely have profound implications charac teristics of HPHT synthetics optical microscopy. From our analysis for how melee diamonds are handled were observed, but most of the HPHT of 883 melee samples in all, we con- in the trade. synthetics showed fluorescence pat- cluded that 857 were natural diamond A parcel of 359 round diamonds be- terns similar to those of natural dia- (97.1%), 24 were HPHT synthetic di- tween 0.02 and 0.03 ct was submitted monds (figure 4). This observation amond (2.7%), and two were HPHT- for identification. They showed uni- emphasizes the importance of in- processed natural diamonds (0.2%). form appearance, intense yellow color, frared absorption spectroscopy, in ad- Wuyi Wang, Martha Altobelli, and good clarity. Based on spectro- dition to DiamondView imaging, Caitlin Dieck, and Rachel Sheppard scopic analysis, each sample’s color was attributed to trace concentrations of isolated nitrogen. Gemological ob- Figure 4. These DiamondView fluorescence images show (A) growth sec- servations, infrared absorption spec- tor patterns typical of HPHT synthetic diamonds, (B) HPHT treatment, troscopy, and DiamondView analysis and (C and D) uncharacteristic HPHT synthetic patterns. confirmed that 344 of them were natural diamonds, 14 were grown by HPHT (high-pressure, high-temperature) synthesis, and one was an HPHT- treated natural diamond (figure 3). Of the 14 synthetic diamonds, eight were dominated by A-aggregate form nitrogen with trace isolated nitrogen, while the other six showed negligible amounts. All had wide- spread pinpoint inclusions, a feature A B typical of HPHT synthetic diamonds. Characteristic growth features of HPHT synthesis were confirmed using a DiamondView fluorescence instrument on six of them. The synthetic diamonds with a high concentration of A-aggregate form nitrogen were produced at much higher temperatures, indicating more than one producer. To gain perspective on the surpris- C D ingly high prevalence of synthetic

294 LAB NOTES GEMS & GEMOLOGY WINTER 2014 VIS-NIR ABSORPTION SPECTRUM Very Large Irradiated Yellow 415.2 Artificial irradiation, with or without 1.2 (N3) annealing, has been used to improve the color of natural diamonds for sev- 1.0 eral decades. This technique is usu- 496.0 503.2 (H4) (H3) ally applied to brownish or light yellow diamonds of relatively small 0.8 size. The New York lab recently ABSORBANCE tested a very large yellow diamond 0.6 that had been artificially irradiated. 595 This emerald-cut stone weighed 22.27 ct and was color graded as Fancy 0.4 Vivid yellow (figure 5). Faint color concentration was observed along the 400 450 500 550 600 650 700 750 800 culet. The diamond showed medium WAVELENGTH (nm) yellow-green, slightly chalky fluorescence to long-wave UV and weak or- Figure 6. The irradiated yellow diamond’s Vis-NIR absorption spectrum, ange fluorescence to short-wave UV. collected at liquid-nitrogen temperature, showed strong absorption from No obvious internal features were ob- the H3 and H4 defects, which were artificially introduced to enhance the served. Its infrared absorption spec- yellow color. trum showed high concentrations of nitrogen and weak absorptions from defects H1b (4935 cm–1) and H1c enhancing its yellow color. This Fancy Kiefert et al., “Cultured pearls from (5165 cm–1). A weak hydrogen-related Vivid yellow color would have been the Gulf of California, Mexico,” absorption at 3107 cm–1 was also de- much lighter and less saturated before Spring 2004 G&G, pp. 26–38) are ex- tected. In the Vis-NIR region, the the treatment. amined in GIA laboratories from time absorption spectrum collected at Artificially irradiated diamonds of to time. But a recent submission to liquid-nitrogen temperature showed this size and attractive color are rarely the New York lab of 10 loose pearls, strong absorptions from the N3, H4, examined in gem laboratories. ranging from 8.17 × 7.65 × 3.89 mm to H3, and 595 nm optical centers (figure Wuyi Wang 17.85 × 11.16 × 6.80 mm (figure 7), 6). These spectroscopic and gemologi- proved interesting owing to their cal features demonstrated that the di- shapes and internal growth features. amond had been artificially irradiated All the pearls had a “grapelike” clus- and annealed to introduce additional Natural PEARL Aggregates from ter appearance, as if multiple smaller absorptions from the H3/H4 defects, Pteria Mollusks pearls had combined into aggre- Both natural and cultured pearls of gates. Their colors ranged from dark Pteria-species mollusks from the Gulf brown and purple to gray, with strong Figure 5. This 22.27 ct Fancy of California, Mexico (M. Cariño and orient consisting of mainly bluish and Vivid yellow diamond was iden- M. Monteforte, “History of pearling pinkish overtones. tified as artificially irradiated in La Paz Bay, South Baja California,” Microscopic examination revealed and annealed. Treated diamonds Summer 1995 G&G, pp. 88–104; L. that the pearls formed with continu- of this size and attractively saturated color are rare. Figure 7. These 10 loose natural pearl aggregates from the Pteria species ranged from dark brown and purple to gray.

LAB NOTES GEMS & GEMOLOGY WINTER 2014 295 Figure 8. Microradiograph images of the pearls revealed multiple growth units with central conchiolin-rich cores in each unit. ous nacre layers. Microradiography coast, which further supports the flattened gas bubbles and voids that further demonstrated that their inter- identity of these unique pieces. are obvious under magnification (S.F. nal structures were composed of mul- Sally Chan and Yixin (Jessie) Zhou McClure et al., “Identification and tiple small pearls related to their durability of lead glass–filled rubies, growth (figure 8). Conchiolin-rich Spring 2006 G&G, pp. 22–34). centers were observed in all of the Lead-Glass-Filled Burmese RUBIES The Carlsbad laboratory recently sub-units, indicating natural forma- Rubies filled with a high-lead-content had the opportunity to examine a tion. Additional advanced testing glass as a clarity enhancement were multi-strand necklace of graduated (UV-Vis reflectance spectrophotome- first reported by the Gemmological round ruby beads (figure 10), measur- try, photoluminescence spectroscopy, Association of All Japan (GAAJ) labo- ing 2.72 to 6.13 mm in diameter. and EDXRF spectrometry) showed ratory in 2004. Since then, many of Standard gemological testing showed that all 10 of the pearls had a natural these stones have been examined by properties consistent with natural color. More importantly, all 10 exhib- gemological laboratories around the ruby. Microscopic observations re- ited medium to strong orangy red to world. They are identified by their nu- vealed typical inclusions for ruby: ru- red fluorescence under long-wave UV, merous large, low-relief fractures and tile silk, banded particulate clouds, which is characteristic of pearls that their blue or orange flashes easily seen twinning planes, red parallel planar form in Pteria mollusks (figure 9). at different angles, as well as their zoning, and roiled graining. The ap- Pearls grown from the aggregation of smaller pearls are sometimes asso- ciated with freshwater culturing prac- Figure 10. The Burmese ruby beads in this multi-strand necklace were tices (Summer 2012 Lab Notes, pp. filled with lead glass. 138–139). Yet these samples clearly did not appear to be cultured. Our client later informed us that the pearls were obtained more than 40 years ago, reportedly off the Mexican

Figure 9. The pearls produced this striking characteristic red fluorescence under long-wave UV.

296 LAB NOTES GEMS & GEMOLOGY WINTER 2014 Figure 11. These wide fractures, Figure 13. Some beads were so filled with glass of relatively low highly fractured and filled that lead content, showed a slightly they would be called “manufac- lower luster than the host ruby. tured products consisting of lead Field of view 2.96 mm. glass and ruby.” This material would easily disintegrate if the Figure 14. This 26.73 ct dark lead glass were removed. Field of pink-purple spinel contained a pearance and chemical composition view 2.96 mm. spinel crystal inclusion. of the beads suggested that their geo- graphic origin was Mogok, Myanmar. Their wide, low-relief fractures (fig- ization showed that the filler con- UV. Observed using a handheld spec- ure 11) and cavities were filled with a tained approximately 43 wt.% PbO, troscope, the stone showed thin ab- foreign substance whose luster was which was much lower than the lead sorption bands near 680 nm, with fine slightly lower than that of the rubies. content reported by McClure et al. in absorption lines near 670 nm. These These observations suggested a lead- 2006 (71–76 wt.%). The diminished gemological properties were consistent glass filler, although the lower luster lead content would lower the refrac- with spinel. was contrary to previous documenta- tive index of the glass and explain the Interestingly, microscopic exami- tion and the filler did not display any lack of flash effect and the lower luster nation showed that the spinel was rel- flash effect. In some beads, the filler observed in this filler. atively free of inclusions except for a also showed a crazed appearance (fig- These beads were the first exam- very low-relief solid inclusion that ure 12) not typically observed in ples of this lower-lead-content glass was only partially visible (figure 15). other rubies filled with high-lead filling in Burmese rubies examined at Examination with polarized light (fig- glass. the Carlsbad laboratory. On a GIA re- ure 16) revealed the entire outline of This strange observation prompted port, most of these beads would be the low-relief crystal. Unaltered crys- us to carry out a chemical analysis identified as “rubies with significant tals generally provide strong evidence of the glass filler. We tested two clarity enhancement with lead glass that a stone has not been heated, and spots using laser ablation–inductively filler.” Yet some of the beads were so this inclusion showed no alteration. coupled plasma–mass spectrometry highly fractured and filled that they But it is also important to consider (LA-ICP-MS) on a relatively large glass- would be considered “manufactured the identity of certain inclusions filled cavity. The results after normal- products consisting of lead glass and when using them as an indication for ruby” (figure 13). thermal treatment. Due to the low re-

Figure 12. In some beads, the Najmeh Anjomani and filler also showed a crazed ap- Rebecca Tsang Figure 15. Under diffused light- pearance not typically observed ing, the outline of the spinel crys- in other rubies filled with lead tal was only partially visible. glass. Field of view 2.96 mm. Spinel Inclusion in SPINEL Image width 3.70 mm. A 26.73 ct transparent dark pink- purple oval mixed cut (figure 14) was submitted to the Carlsbad laboratory for identification services. Standard gemolo gical testing showed a refractive index of 1.719 and a hydrostatic specific gravity of 3.59. The stone flu- oresced very weak red to long-wave UV light and was inert to short-wave

LAB NOTES GEMS & GEMOLOGY WINTER 2014 297 PL SPECTRA

90000 685.5 Spinel, no indication of heating 80000 Spinel, heated

70000

60000

50000

0.92 nm Figure 16. Under polarized light- 40000 ing, the outline of the spinel crystal was clearly visible. Image 30000 687.5 width 3.70 mm. INTENSITY (COUNTS) 20000 lief of this inclusion, it is very likely 10000 6.11 nm a spinel inside of spinel. Their match- 0 ing refractive index explains why the 620 640 660 680 700 720 740 760 780 inclusion is nearly invisible. Since the WAVELENGTH (nm) host and inclusion are the same material, we would not expect to see any Figure 18. The gray spectrum of unheated spinel shows that the FWHM (full alteration due to heat treatment. width at half maximum) of the peak with highest counts is 0.92 nm and the Therefore, the unaltered appearance position of the peak is at 685.5 nm. The purple spectrum, representing the of this inclusion cannot be used to de- dark pink-purple spinel, shows that the FWHM of the peak with highest termine that this spinel has not been counts is 6.11 nm and the peak is shifted from 685.5 to 687.5 nm. heat treated. The spinel’s visible absorption spectrum revealed that its purple et al., “Optical spectrum of Cr3+ ions the Fe2+/Fe3+ charge transfer and Fe2+ color results from the combination of in spinels,” The Journal of Chemical cause the absorption bands from 590 Fe and Cr (figure 17). Absorption Physics, Vol. 48, No. 11, 1968, pp. to 700 nm (S. Muhlmeister et al., bands with a maximum at 400 and 5255–5262). Fe2+ causes the absorp- “Flux-grown synthetic red and blue 550 nm are caused by Cr3+ (D.L. Wood tion band from 400 to 590 nm, while spinels from Russia,” Summer 1993 G&G, pp. 81–98). Spinels submitted to GIA’s labo- Figure 17. The spinel’s visible spectrum revealed that its dark pink-purple ratory are routinely checked using color was caused by Cr and Fe. advanced analytical tools. Laser ablation–inductively coupled plasma–mass VISIBLE SPECTRUM spectrometry (LA-ICP-MS) was used to confirm the natural trace elements. Fe2+ Fe2+/Fe3+ charge transfer and Fe2+ Higher concentrations of Li (27.7 Cr 3+ 400 ppmw), Be (87.4 ppmw), Zn (133 ppmw), and Ga (63 ppmw) indicate a 0.5 natural origin, and the specimen’s photoluminescence (PL) spectrum was 590 3+ consistent with a heated spinel due to 0.4 Cr 550 the broad full width at half maximum (FWHM) observed at 687.5 nm (figure 0.3 18; see S. Saeseaw et al., “Distinguish- ing heated spinels from unheated natural spinels and from synthetic 0.2 ABSORBANCE (a.u.) ABSORBANCE spinels,” GIA Research News, April 2009, http://www.gia.edu/gia-news-

0.1 research-NR32209A). It was unusual to see a spinel with this dark pink- Dark pink-purple spinel purple color showing evidence of 0 heat, as we typically see only red 400 450 500 550 600 650 700 WAVELENGTH (nm) spinels that have been heated. From careful microscopic examination and

298 LAB NOTES GEMS & GEMOLOGY WINTER 2014 UV-VIS-NIR ABSORPTION SPECTRUM advanced gemological testing, we 393.4 were able to conclude that this was a [ND1] 503.2 natural spinel showing indications of [H3] 0.4 516.1 heating. 575.0 741.2 [N-V]0 636.9 GR1 Amy Cooper and Ziyin Sun [N-V]–

594.4

CVD SYNTHETIC DIAMOND with 0.3 Fancy Vivid Orange Color ABSORBANCE 736.6 736.9 With the rapid improvement of CVD [Si-V]– synthetic diamond quality in recent years, various colorations can be in- 0.2 troduced after growth. The New York laboratory recently tested a CVD syn- 400 450 500 550 600 650 700 750 800 thetic with a very attractive orange WAVELENGTH (nm) color. This round-cut specimen weighed Figure 20. Several defects were detected in the CVD synthetic diamond’s 1.04 ct and was color graded as Fancy absorption spectrum in the UV-Vis-NIR region at liquid-nitrogen tempera- Vivid pinkish orange (figure 19), a very ture. Strong absorptions from the N-V centers are the main cause of the ob- rare color among natural and treated served pinkish orange color. diamonds. Except for a few dark pinpoint inclusions, it showed no notable internal features. Under crossed polar- related side bands. We also recorded the relatively high concentration of izers, it displayed natural-looking absorptions from some irradiation-re- [Si-V]– could be attributed to the treat- “tatami” strain patterns. Absorption lated defects, including 594.4 nm, ment by combining preexisting Si im- spectroscopy in the infrared region GR1 at 741.2 nm, ND1 at 393.4 nm, purity with artificially introduced showed typical type IIa features, with and the general radiation absorption vacancies. With further developments no detectable defect-related absorp- features at 420–450 nm. Also ob- in after-growth treatment, it is highly tion. At liquid-nitrogen temperature, served were weak absorptions from likely that more colors in CVD syn- a few absorption features were de- the H3 defect at 503.2 nm, possible thetic diamonds will be introduced. tected in the UV-Vis-NIR region (fig- nickel-related defects at 516.1 nm, Wuyi Wang and Kyaw Soe Moe ure 20). The major ones include and [Si-V]– at 736.6/736.9 nm. Under absorptions from N-V centers with the strong short-wave UV radiation of ZPL at 575.0 and 636.9 nm, and their the DiamondView, the sample showed very strong red fluo rescence Mixed-Type HPHT with sharp linear growth striations, a SYNTHETIC DIAMOND with Figure 19. This 1.04 ct round was unique feature of CVD synthetic dia- Unusual Growth Features identified as a CVD synthetic di- mond. Weak red phosphorescence A 0.28 ct round brilliant was submit- amond. Its Fancy Vivid pinkish was also detected. These observations ted as synthetic moissanite to the orange color was introduced confirmed that this was a CVD syn- Carlsbad lab for an identification re- through post-growth irradiation thetic diamond with post-growth port. At first glance, synthetic mois- and annealing. treatments. Nitrogen concentration, sanite seemed like a possibility. The based on absorptions in infrared ab- stone had a green-yellow color and sorption spectroscopy, was below 1 contained numerous growth tubes ppm. After initial growth, the sample visible through the table (figure 21). was artificially irradiated and then an- Yet it did not show doubling in the nealed at moderate temperatures to microscope, which is a characteristic introduce the N-V centers. Strong ab- feature of synthetic moissanite. Its in- sorptions from N-V centers are the frared spectrum was a match for dia- main causes of the observed pinkish mond. The infrared spectrum also orange bodycolor. showed a very unusual combination The very attractive orange color of boron and nitrogen impurities at was achieved by introducing the 2804 and 1130 cm–1, respectively (fig- proper concentrations of N-V centers ure 22). These two impurities are not while limiting the formation of other known to occur together in natural di- defects. It should be pointed out that amonds in measurable quantities.

LAB NOTES GEMS & GEMOLOGY WINTER 2014 299 IR SPECTRUM

2.2

2.0

93 1130 cm–1–1 1.8 92

91 1.6 00.9.9 13001200 1100 28042804 ccmm–1–1 1.4 Figure 21. These growth tube ABSORBANCE (a.u.) ABSORBANCE features were visible through the 1.2 table of the HPHT-grown synthetic diamond. Magnified ap- 1.0 proximately 90×.

5000 4000 3000 2000 1000 This was a strong indicator of syn- WAVENUMBER (cm–1) thetic origin. A DiamondView image (figure 23) confirmed that it was synthetic, grown by the high-pressure, Figure 22. The HPHT-grown synthetic diamond’s infrared spectrum shows high-temperature (HPHT) method. It peaks related to both boron and single nitrogen. is noteworthy that after the sample was removed from the DiamondView, it showed very strong blue phospho- boron and nitrogen are allowed to in- thetic moissanite, they could be seen rescence that was clearly visible in corporate into the lattice, the blue and growing in different directions in this ambient room lighting and persisted yellow bodycolors will combine to synthetic diamond. The tubes in syn- for several minutes. produce a green color (J.E. Shigley et thetic moissanite also tend to be very Unless special precautions are al., “Lab-grown colored diamonds straight, while the ones in this sample taken, diamond synthesis will incor- from Chatham Created Gems,” Sum- curved and changed direction. Al- porate nitrogen into the lattice, which mer 2004 G&G, pp. 128–145). Since though this stone bore some superfi- leads to a yellow bodycolor. Certain boron is an electron acceptor and nitro- cial resemblance to moissanite, its chemicals can be added to prevent the gen is an electron donor, an excess of gemological properties were quite dif- incorporation of nitrogen, and this can boron will compensate the nitrogen ferent, another reminder to avoid lead to colorless diamonds. If boron is and the blue color will predominate. quick sight identifications. introduced to the growth of synthetic Because nitrogen and boron have slight Troy Ardon diamonds, it will become incorporated preferences for different growth sec- and produce a blue bodycolor. If both tors, if the concentration of both nitrogen and boron is carefully controlled, A Larger, Higher-Quality NPD nitrogen and boron will dominate dif- SYNTHETIC DIAMOND Figure 23. This DiamondView ferent growth sectors. The colors will In February 2014, these authors re- image shows the characteristic blend to create a face-up greenish color ported the first example of a syn- growth pattern of an HPHT syn- (R.C. Burns et al., “Growth-sector de- thetic nano-polycrystalline diamond thetic diamond. pendence of optical features in large (NPD) detected by a gemological lab- synthetic diamonds,” Journal of Crys- oratory (see www.gia.edu/gia-news- tal Growth, Vol. 104, No. 2, 1990, pp. research-fancy-black-NPD-synthetic). 257–279). The 0.9 ct marquise was small and so The growth tubes in this sample heavily included with graphite crys- were an unusual feature, last seen in tals as to receive a Fancy Black color a selection of HPHT-grown synthetics grade. The East Coast laboratory re- several years ago at GIA’s West Coast cently detected another undisclosed laboratory. They appear similar to NPD synthetic diamond, a 1.51 ct synthetic moissanite growth tubes, Fancy Black round. though there are a few key differ- This NPD specimen was larger and ences. Whereas the growth tubes had a much better transparency than occur in only one direction in syn- the previous NPD, though it still

300 LAB NOTES GEMS & GEMOLOGY WINTER 2014 MID-IR SPECTRA

One-phonon region ABSORBANCE

Figure 24. This 1.51 ct Fancy Black nano-polycrystalline diamond (NPD) synthetic, submitted undisclosed, was larger and showed much better transparency than a previously de- 5000 4500 3000 2000 1000 tected NPD synthetic. WAVENUMBER (cm–1) graded as Fancy Black (figure 24). In- Figure 25. The mid-FTIR spectrum of the 1.51 ct black NPD synthetic dia- frared spectroscopy showed a diagnos- mond (red) displayed absorption in the one-phonon region similar to that tic absorption pattern for diamond, of known NPD samples (green). with strong absorption in the one- phonon region (approximately 400– 1332 cm–1). Absorption in this region is sample to be a NPD synthetic dia- cluded with graphite, but less so than usually attributed to nitrogen impurity mond. Microscopic observation re- the previously reported 0.9 ct mar- in different aggregation states, but vealed that the host material had the quise, and therefore it had a better careful observation showed otherwise. yellow color typical of previously re- transparency (figure 26). The specimen’s infrared absorption ported NPD samples (see E.A. The origin of this synthetic dia- pattern matched that of known NPD Skalwold, “Nano-polycrystalline diamond is not known, but it showed ob- samples (figure 25). Further testing, mond sphere: A gemologist’s perspec- vious improvements in size and including Raman spectroscopy and tive,” Summer 2012 G&G, pp. quality compared to the marquise re- DiamondView imaging, confirmed the 128–131). The sample was heavily in- ported in February 2014. In the future, NPD synthetics could pose an identification challenge to the gem and jewel ry industry. Careful gemological Figure 26. These photomicrographs, magnified 35× (left) and 40× (right), observations and advanced testing show abundant inclusions of graphite inclusions. Note the yellow color of techniques were required to identify the host material. this undisclosed synthetic diamond. Paul Johnson and Kyaw Soe Moe

PHOTO CREDITS: Johnny Leung—1; Sood Oil (Judy) Chia— 3, 5, 7, 19; Martha Altobelli and Caitlin Dieck—4; Yixin (Jessie) Zhou—8; Jian Xin (Jae) Liao—9, 24; C.D. Mengason—10; Nathan Renfro—11–13; Robison Mc- Murtry—14; Ziyin Sun—15, 16; Troy Ardon—21, 23; Paul Johnson—26.

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