Editors Thomas M. Moses | Shane F. McClure

Graphite Inclusions Forming specific growth episode when oxi- dized fluids rich in CO and H O Octahedral Outline in DIAMOND 2 2 Primary diamond deposits are usually passed through diamond bearing hori- found in mantle-derived igneous zons. This also explains the shift of rocks, with the principal hosts being the G band to a higher energy, due to kimberlite and lamproite. During the the higher strain near these newly ascent to the earth’s surface, dia- formed secondary graphite crystals (J. monds may be converted, partially or Hodkiewitcz, “Characterizing graph- entirely, to graphite and chemically ene with Raman spectroscopy,” dispersed and eliminated (A.A. Application Note: 51946, Thermo Fisher Scientific, Madison, Wiscon- Snelling, “Diamonds – Evidence of sin, 2010). Late formation of addi- explosive geological processes,” Cre- tional diamond layers on top of the ation, Vol. 16, No. 1, 1993, pp. 42– graphites would have converted them 45). GIA’s New York laboratory to covered internal features within recently received a 1.30 ct Fancy the larger diamond (R.H. Mitchell, brownish greenish yellow diamond Kimberlites and Lamproites: Pri- (figure 1) containing an octahedral- mary Sources of Diamond, Geo- shaped inclusion outlined by minute Figure 1. This 1.30 ct Fancy science Canada Reprint Series 6, Vol. crystal inclusions along the junctions brownish greenish yellow dia- of the crystal faces. mond contains an octahedral- Gemological examination at 60× shaped inclusion. magnification reveals that the octahe- Figure 2. Minute graphite inclu- dral-shaped inclusion is outlined by sions outline the octahedral crys- numerous irregular dark crystals (fig- clusions are graphite crystals with a tal faces in this diamond. Field of ure 2). Advanced gemological analysis Raman peak at 1590 cm–1 (figure 3), view 7.19 mm. with UV-Vis and FTIR spectroscopy which corresponds to the graphite G confirmed that this was a natural dia- band (I. Childres et al., “Raman spec- mond with a natural color origin. troscopy of graphene and related ma- Further analysis using Raman terials,” in J.I. Jang, Ed., New spectroscopy reveals that the dark in- Developments in Photon and Mate- rials Research, Nova Science Publica- tions, 2013). Since this G band is at a slightly higher energy level than that from the primary graphite, which Editors’ note: All items were written by staff usually peaks at around 1580 cm–1 , members of GIA laboratories. we propose that the crystals tested GEMS & GEMOLOGY, Vol. 51, No. 4, pp. 428–440. are likely the secondary graphite con- © 2015 Gemological Institute of America verted from part of the original dia- mond into graphite form during the

428 LAB NOTES GEMS & GEMOLOGY WINTER 2015 RAMAN SPECTRUM diamonds. As seen in figure 6 (left), the cubic {100} sector can be located in the pavilion, along with octahedral 7000 {111} sectors. In order to understand more about this growth, we compared it with a type IIa 0.27 ct HPHT syn- thetic, which was treated post-growth to induce a Fancy Intense orangy pink 6000 color (figure 6, right). Both specimens showed similar fluorescence patterns; however, the natural diamond’s 1590

COUNTS greenish blue phosphorescence was 5000 evenly distributed, as seen in the mid- dle image of figure 6. This is unlike the dark images yielded from type IIa pink HPHT synthetics, which are not phosphorescent. 4000 Although most natural diamonds show octahedral growth structure in

2000 1900 1800 1700 1600 1500 1400 DiamondView images, some natural gem-quality colorless and yellow dia- RAMAN SHIFT (cm–1) monds may show cuboctahedral growth (Winter 2010 Lab Notes, pp. Figure 3. The graphite G band at 1590 cm–1 is found on the minute crys- 298–299; Winter 2011 Lab Notes, p. tals along the crystal junctions, confirming that they are graphite crystals. 310; Spring 2013 Lab Notes, pp. 45– 46). Some non-gem-quality diamonds possess cuboctahedral form (D.G. Pearson et al., “Orogenic ultramafic rocks of UHP (diamond facies) ori- 18, No. 1, 1991, pp. 1–16). Primary Treated Pink with HPHT Synthetic gin,” in R.G. Coleman and X. Wang, graphite crystals could also mix into Growth Structure Eds., Ultrahigh Pressure Metamor- the crystal clouds during the dia- HPHT synthetic diamonds are grown phism, Cambridge University Press, mond’s growth due to changes in en- using high pressure and high tempera- 1995, pp. 456–510). Growth rate, pres- vironmental temperature, pressure, ture but with a much higher growth sure, and temperature of geological and the growth fluid’s chemical ele- rate than natural diamond. Conse- environment control the habit of a di- ments. These minute graphite crys- quently, their growth structures are dif- tals would tend to form along the ferent. GIA’s New York lab recently junctions of crystal faces, since they examined a multi-step treated diamond usually have a higher surface energy. with a growth structure similar to that Figure 4. This multi-step treated Thus, we believe that both primary of HPHT synthetics. The 1.62 ct Fancy 1.62 ct Fancy pink natural dia- and secondary graphite formation, oc- pink type IIa round brilliant seen in fig- mond shows what appears to be curring between the diamond’s ure 4 showed spectral characteristics HPHT synthetic growth structure. growth episodes, contributed to this suggestive of HPHT treatment, irradi- phenomenal octahedral outline. ation, and annealing. This diamond Graphite inclusions are commonly was internally clean, except for the seen in diamonds as isolated crystals presence of strong, colorless internal or jointed crystal clouds. It is very un- graining (figure 5). Tatami and banded usual to see these minute graphite in- strains with strong interference colors clusions formed at the junctions of the could be seen under cross-polarized original diamond crystal faces and out- light (again, see figure 5). Based on these lining the octahedral growth pattern. microscopic features, we concluded This stone not only captures the that this was a natural diamond. amount of stress and extreme condi- DiamondView imaging of the tions under which the diamond grew, stone showed cuboctahedral growth but also shows the beauty of the for- with dark sectors and pink coloration mation of crystalline diamond. (figure 6). This crystal habit is usually Yixin (Jessie) Zhou observed in HPHT-grown synthetic

LAB NOTES GEMS & GEMOLOGY WINTER 2015 429 Figure 5. Tatami strain (left, field of view 3.20 mm), banded strain (middle, field of view 3.20 mm), and heavy in- ternal graining (right, field of view 2.45 mm) are evidence of a natural diamond.

amond crystal. A slow growth rate Very Large Type Ib Natural cently tested a large 13.09 ct gem- causes octahedral crystal growth, but Diamond quality natural type Ib rough dia- a high growth rate can facilitate cubic Nitrogen is the main impurity in dia- mond. The diamond measured 13.51 {100} and octahedral {111} sectors de- mond and during growth it is initially × 11.56 × 10.18 mm, with rounded do- veloping simultaneously. As a result, incorporated in the diamond lattice as decahedral morphology and clear dis- cuboctahedral habit can be formed isolated nitrogen atoms (C centers). solution pits on some faces in a naturally. Diamonds where the majority of nitro- symmetrical pattern (figure 7). The di- While the DiamondView is very re- gen occurs in C centers are known as amond had a highly saturated, slightly liable at revealing the growth structure type Ib. While C centers are common orangy yellow color evenly distrib- of natural vs. synthetic diamond, it is in lab-grown HPHT diamonds, the oc- uted throughout the whole crystal. important to correctly interpret all currence of C centers in natural cra- The diamond contained two tiny sul- identifying characteristics. When tonic diamonds is extremely rare (<1% fide inclusions with their associated cuboctahedral growth structure is ob- of all natural diamonds). Natural dia- graphitic rosette fracture systems. served, one should look for other monds form deep in Earth’s mantle, The infrared absorption spectrum features to support the origin. Micro- where high temperatures result in ni- revealed typical features of natural scopic features and spectral character- trogen aggregating to form A centers type Ib diamonds: a sharp peak at istics are useful for this purpose. (N ) and B centers (N V). 1344 cm–1 and a broad band at 1130 S 4 Kyaw Soe Moe and Wuyi Wang GIA’s New York laboratory re- cm–1. The absorption attributed to the

Figure 6. DiamondView fluorescence images of the treated 1.62 ct pink natural (left) and the post-growth treated 0.27 ct pink HPHT synthetic (right) showed similar growth patterns, containing cubic {100} sector and octahedral {111} sectors. The middle image of phosphorescence of the 1.62 ct pink natural diamond showed even color distri- bution without growth sectors. Type IIa pink HPHT synthetic diamonds are usually not phosphorescent.

{111}

{111} {111} {100} {111} {100} {111}

{111}

430 LAB NOTES GEMS & GEMOLOGY WINTER 2015 monds. Preservation of C centers in hyalite opal from Zacatecas, Mexico,” these natural diamonds is typically at- Journal of Gemmology, Vol. 34, 2015, tributed to very young formation ages pp. 490–508). or to storage of these diamonds at GIA’s Tokyo laboratory recently cooler temperatures in Earth’s mantle had an opportunity to examine sev- than most other diamonds. Ongoing eral faceted hyalites from Zacatecas, isotopic age dating of sulfide inclu- Mexico, along with several rough sions, combined with temperature hyalites from other locations, includ- constraints, will provide the opportu- ing Japan, Hungary, and Argentina. nity to evaluate how these enigmatic There were two different types of type Ib diamonds are preserved in nat- Japanese hyalites in the study sam- ural cratonic settings. ples: botryoidal and spherical. The Wuyi Wang and Karen Smit botryoidal one (figure 9) was from Gifu’s Naegi granitic pegmatite (H. Ogawa et al., “Fluorescence of hyalite in pegmatite from Naegi granite, Figure 7. The yellow color of this Uranium Contents of HYALITE Hyalite is a colorless variety of com- Nakatugawa,” 2008 Annual Meeting gem-quality 13.09 ct type Ib nat- of Japan Association of Mineralogical ural diamond rough is due to mon opal with strong greenish fluo- Sciences), while the spherical one was the presence of isolated nitrogen rescence. Rough specimens have from Toyama’s Shin-yu hot spring (Y. (C centers). interesting glassy botryoidal shapes formed by vapor transport in volcanic Takahashi et al., “On the occurrence or pegmatitic environments (O.W. of opal at the Shin-yu hot spring, Flörke, “Transport and deposition of Tateyama,” Tateyama Caldera Re- A center (1280 cm–1) was rather weak. SiO with H O under supercritical search, Vol. 8, 2007, pp. 1–4.). Hungar- 2 2 Spectral fitting showed that 75% of conditions,” Kristall und Technik, ian hyalite is known to form in the the nitrogen existed as C centers and Vol. 7, 1972, pp. 159–166). Hyalite clefts of trachytic rocks in Bohemia, 8% as A centers. This diamond did from a new source in Zacatecas, Mex- Czech Republic, and Auvergne, not contain any amber centers, which ico, discovered in 2013, shows strong France (B. von Cotta, Rocks Classified is consistent with the lack of plastic green fluorescence even under day- and Described: A Treatise on Lithol- deformation lines or brownish hue. light conditions. This material was ogy, Longmans, Green, and Company, The UV-Vis-NIR absorption spec- spotlighted for the first time at the London, 1866, p. 425). Argentinean trum, collected at liquid nitrogen tem- 2014 Tucson gem and mineral shows hyalite is widely distributed, but the perature, showed a smooth and gradual (E. Fritsch et al., “Green-luminescing original rocks are not described. increase in absorption from the near- infrared region to about 560 nm, and then a sharp increase to the high-en- Figure 8. The diamond’s PL spectrum, collected at liquid nitrogen temper- ergy side. C centers were the only ature with 514 nm laser excitation, showed emissions related to N-V cen- color-introducing defect in this large ters along with many sharp peaks of unknown assignment. diamond. Photoluminescence (PL) spectra were collected at liquid nitrogen PL SPECTRUM 50000 temperature with various laser exci- Diamond 637.0 tations. Under 514 nm laser excita- 45000 Raman [N-V]- 0 – tion, [N-V] at 574.9 nm and [N-V] at 40000 624.4 637.0 nm were detected. Many sharp 657.8 35000 574.9 emissions with unknown assign- [N-V]0 614.3 ments were also observed (figure 8). 30000 586.2 With 830 nm laser excitation, weak 25000 585.8 640.3 575.4 589.1 626.2 600.4 emissions at 882/884 nm from Ni- 621.6 20000 589.9 635.2 610.9 related defects were observed. 582.9 INTENSITY (CPS) 595.6 15000 Large type Ib diamonds with in- 581.2 tense yellow color are rarely seen. 10000

GIA continues to study these rare di- 5000 amonds to understand the geological 550 570 590 610 630 650 processes that allow isolated nitrogen WAVELENGTH (nm) to be preserved in some natural dia-

LAB NOTES GEMS & GEMOLOGY WINTER 2015 431 Figure 9. Two different types of Japanese hyalite rough specimens under daylight (left) and short-wave UV light (right). The photo on the right demonstrates the strong yellow-green fluorescence of pegmatite hyalite, while the spherical hyalite samples do not show the fluorescence.

Standard gemological testing of the spectra composed of a major band be- (LA-ICP-MS) detected a very wide range faceted Mexican stones revealed RI val- tween 430 and 460 cm–1 (vibration of of uranium contents; the maximum ues of 1.460–1.461 and a hydrostatic SG bridging oxygen) and a band centered was 1060–1330 ppmw for the Japanese of 2.13. Prominent fluorescence was at 790 cm–1 representing the stretching pegmatitic hyalite, while the Japanese observed under short-wave UV light, of isolated SiO 4– (P. McMillan, “A spherical hyalite had zero uranium 4 but only the Japanese spherical samples Raman spectroscopic study of glasses content. The amounts are quite inho- were inert (figure 10). Strong graining in the system CaO-MgO-SiO ,” Amer- mogeneous, but seem to correlate with 2 flow structures were visible at 64× ican Mineralogist, Vol. 69, 1984, pp. the intensities of fluorescence, decreas- magnification. Raman analysis (figure 645–659). Laser ablation–inductively ing from Mexican (1180–3.55 ppmw) to 11) revealed typical amorphous silica coupled plasma–mass spectrometry Argentinian (2.48–2.49 ppmw) to Hun- garian (0.39–0.15 ppmw) (figure 11). Interestingly, only the Japanese peg- Figure 10. Clockwise from top center, one Hungarian botryoidal hyalite matitic hyalite sample was rich in rare with matrix, one Japanese pegmatite rough hyalite with matrix, twenty- earth elements (REE). Since Naegi three pieces of Japanese spherical hyalite, one rough and three faceted granitic pegmatite is known to be an Mexican specimens, and one Argentinian botryoidal hyalite under short- REE-enriched pegmatite (T.S. Ercit, wave UV light. The intensity of yellow-green fluorescence vary in the dif- “REE-enriched granitic pegmatites,” in ferent specimens. R.L. Linnen and I.M. Samson, Eds., Rare-Element Geochemistry and Min- eral Deposits, Geological Association of Canada, GAC Short Course Notes 17, 2005, pp. 175–199), the host rock chemistry appears to affect the silica- rich fluid. Kazuko Saruwatari, Yusuke Katsurada, Shoko Odake, and Ahmadjan Abduriyim

Large Natural Fossil Blister PEARLS from Tr dacna (Giant Clam) Species Fossil pearls, first mentioned in 1723 in John Woodward’s “An essay to- wards a natural history of the earth and terrestrial bodies,” were described in greater detail by R. Bullen Newton in 1908 (“Fossil pearl-growths,” Jour- nal of Molluscan Studies, Vol. 8, pp.

432 LAB NOTES GEMS & GEMOLOGY WINTER 2015 RAMAN SPECTRA

442 790

a

b

c

d INTENSITY

Figure 12. Two natural fossil blis- e ter pearls attached to their giant clam host, courtesy of Volker Bassen London Auction Rooms.

f

these pearls had a porcelaneous ap- g pearance and were smoother than the bases, which were attached to the clam shell. These bases showed 200 1200 2200 3200 chalky rough surfaces and flared RAMAN SHIFT (cm–1) forms (figure 13). Numerous natural indentations and cavities were pres- Figure 11. Raman spectra from (a–b) Mexican hyalites, (c) Japanese peg- ent on their surfaces. In some areas, matitic hyalite, (d) Hungarian hyalite, (e) Argentinean hyalite, and (f–g) subtle flame-like structures were also Japanese spherical hyalite. All spectra show similar patterns, with the observed at 10× magnification with Mexican specimens showing the unknown specific peak at 1548 cm–1. the use of fiber-optic lighting (figure 14). Microradiography was not helpful owing to the specimens’ sizes, but Raman spectroscopy was able to de- 318–320). It is a rare occurrence to re- move the entire shell from the tect calcite on both specimens and ceive such pearls at GIA, which is ground. Similar fossilized giant clam aragonite on the larger pearl, although why two large fossil blister pearls re- shells have been recovered from areas it is possible there was aragonite in cently submitted to the New York lab- along the Kenyan coastline (G. Ac- untested areas on the small pearl. The oratory immediately caught our cordi et al., “The raised coral reef presence of aragonite in the larger attention. complex of the Kenyan coast: Tri- pearl indicates that some of those According to the client, the pair of dacna gigas U-series dates and geolog- structures had been replaced by cal- fossil blister pearls were found near ical implications,” Journal of African cite during fossilization. Lunga Lunga, a region in southeastern Earth Sciences, Vol. 58, No. 10, 2010, According to the client, the shell Kenya bordering Tanzania. They were pp. 97–114). These two blister pearls in figure 12 was found in the upper found attached to a fossilized giant were subsequently removed from the layers of secondary fossil reef build- clam shell that weighed approxi- shell and submitted to GIA for iden- up, suggesting that it lived there dur- mately 297 kg and was discovered 4.3 tification after cleaning and removing ing the later Pleistocene period. To meters below ground (figure 12) along the outermost fossilized debris. the authors, the shell looks similar to with some fossilized corals. The shell, The blister pearls measured ap- that of the present-day Tridacna gigas along with the attached pearls, was proximately 58 × 47 × 45 mm and 85 giant clam, but the client stated that presented to the client as a gift from a × 70 × 46 mm and weighed 758 ct and the clam was a precursor called Tri- local Digo tribe. It took a month to re- 1256 ct, respectively. The faces of dacna gigantea. The large size of

LAB NOTES GEMS & GEMOLOGY WINTER 2015 433 Figure 13. The two natural fossil blister pearls after removal from the giant clam shell. The left image shows the face-up view, while the right image shows the base of the pearls, where the clam shell was previously attached.

these fossil blister pearls, their unique process. Gemologists are never sure different from anything encountered, appearance, and the story behind their what they will find when natural to our knowledge, in a natural pearl. discovery proved fascinating, and of- pearls are examined using microradi- RTX revealed an attractive radiating fered valuable gemological and scien- ography. Substantial real-time X-ray structure within a central conchiolin- tific information for future reference. microradiography (RTX) work by GIA rich boundary and associated external Chunhui Zhou and staff in various locations has shown arcs within the surrounding nacreous Joyce Wing Yan Ho evidence of formation cause in only a overgrowth (figure 16). The radial ob- few pearls. ject displayed clear solid arms extend- Early in 2015, a cream semi- ing from the central core of the baroque button pearl measuring 5.22 structure. Given the nature of the A Natural Pearl with an Intriguing × 5.04 mm and weighing 0.95 ct (fig- core, further investigation was per- Internal Structure ure 15) was submitted to GIA’s formed in order to identify the radial Aspects of natural pearl formation re- Bangkok laboratory with nine other feature and see whether the pearl was main a mystery in many cases; how- pearls. Externally the pearl appeared natural or formed via human inter- ever, one generally accepted principle similar to many other previously ex- vention using an organic nucleus as a is that an intruder finds its way into amined natural pearls, but the micro- “bead.” the mantle or gill areas of a mollusk radiography uncovered something Computed microtomography (μ- and instigates the pearl formation that was far from normal. CT) analysis was used to perform a 3- After initial RTX examination, D examination of the radial feature. the apparent initiator of this speci- The μ-CT results revealed a magnifi- Figure 14. Porcelaneous and men’s formation was found to be very cent structure with a snowflake-like flame-like structures, seen here on the surface of the larger fossil blister pearl, were observed in some areas under fiber-optic Figure 15. The 0.95 ct pearl measuring 5.22 × 5.04 mm is shown with a lighting. Field of view 15 mm. GIA triplet loupe for scale.

434 LAB NOTES GEMS & GEMOLOGY WINTER 2015 Figure 16. The RTX images of the pearl’s structure (left and right viewed from the side; center viewed from the top) revealed an intricate feature that might be an example of a foraminifera. The central feature measures approxi- mately 1.95 × 1.93 mm, as determined by RTX and μ-CT. intricacy to its form (figure 17). The have been documented in RTX and μ- hole present in the shell, as opposed to structure created some doubts about CT work carried out on two pearls re- the larger drill holes commonly found the natural formation of the pearl. The covered from natural P.maxima shells in cultured pearls, also strongly sug- dark organic/conchiolin-rich growth by GIA staff (“An expert’s journey into gests a natural origin. structure, with some gaps between the the world of Australian pearling,” The nucleus of the 0.95 ct pearl nucleus and the surrounding nacre, 2014, www.gia.edu/gia-news-press/ under discussion appeared to be an or- has been noted in other unusual natu- malaysia-jewellery-fair). Pearls with ganism such as coral. In order to find a ral pearls of known origin. This differs unique structures have also been re- match, coral samples were analyzed by from the so-called “atypical bead-cul- ported by others (K. Scarratt et al., RTX and μ-CT methods to compare tured pearls” that almost always dis- “Natural pearls from Australian Pinc- their structures. Results indicated that play a tight structure (lacking growth tada maxima,” Winter 2012 G&G, pp. the feature within the pearl may well arcs) around the inserted nucleus. Al- 236–261). The exact origin of the pearls be coral, but no exact match was most all of the whole shell nuclei ex- studied in Scarratt et al. is unclear, al- noted. During the recent International perimentally inserted into Pinctada though they are more likely to be nat- Gemmological Conference (IGC) in maxima hosts have shown the bound- ural in at least two of the examples Vilnius, Lithuania, it was suggested ary of the shell/nacre interface to cited. For instance, the whole shell of that the similar internal feature of a merge tightly with one another, with one sample mentioned by Scarratt et al. different pearl (N. Sturman et. al, “X- very little in the way of organic arcs showed characteristics similar to the ray computed microtomography (μ- within the surrounding nacre. This cu- specimen described here, with visible CT) structures of known natural and rious structure led to further investiga- arcs within the nacre surrounding a non-bead cultured Pinctada maxima tions into published claims of natural shell nucleus that has a notable pearls,” Proceedings of 34th Interna- organic nuclei within natural pearls. void/organic interface between the tional Gemmological Conference, Similar but not identical structures shell and nacre. The very small drill 2015, pp. 121–124) could well be a re-

Figure 17. The μ-CT images reveal the structure in even more detail. Here, the nature of the organic-looking nat- ural core is shown in three different μ-CT slices in the three different directions examined.

LAB NOTES GEMS & GEMOLOGY WINTER 2015 435 markably preserved foraminifera, a marine micro-skeleton member of a phylum of amoeboid protists. They are usually less than 1 mm in size; their structures vary, and many live on the sea floor. Given the environment, size, and features evident in the form within the pearl under discussion, it may well be that the internal structure is a type of foraminifera sphere with a porous structure for passive filtration (see figure 6 at www.mdpi.com/1660- 3397/12/5/2877/html). The μ-CT re- sults revealed the interconnecting channels and radial structure charac- teristic of these spherical foraminifera. Whatever the true nature of the central form, the author considers the structure of this pearl to be natural Figure 18. Left: A large natural pearl reportedly from a Spondylus species. based on the characteristics noted. It Right: A large natural pearl reportedly from a Trochoidea species. Cour- is also interesting to see that this tesy of Sunghee Caccavo. pearl was small and not of particu- larly fine quality, other characteris- tics of natural pearl samples collected from the field. GIA’s own experi- abundant surface grooves, and a dis- and their appearances closely resem- ments with small pieces of shell and tinct bluish flame structure (figure 19). ble one another. coral using P. maxima hosts have pro- As with previous examples, microra- Our client claimed that the duced larger pearls with different ex- diography showed only a tight struc- Spondylus pearl is from Baja, Mexico; ternal appearances and generally finer ture, lacking obvious growth arcs. In the turban pearl is from Mexico’s Pa- quality than the specimen studied addition, aragonite and natural poly- cific coast. Although it is extremely here. Further research into the differ- enic pigment peaks were detected by challenging to identify the exact mol- ences between unusual structures in Raman spectroscopy. Its unique ap- lusk species these rare pearls origi- natural and atypical bead-cultured pearance, coloration, and bluish tinted nated from, their unique and pearls will continue. flame structures consistent with interesting appearances are consistent Spondylus pearls we previously re- with previously studied materials of Nanthaporn Somsa-ard ported. There is no known cultured similar claims. Regardless of their pearl from this species, and the tight structure is commonly seen in other Two Large Natural Pearls non-nacreous pearls, which further Figure 19. Distinct bluish flame Reportedly from Spondylus and confirmed its natural origin. structures were observed on this Trocho dea Species Mollusks The same client also submitted a large non-nacreous pearl, similar In a Fall 2014 Lab Note (pp. 241–242), large natural nacreous pearl report- to previously studied samples GIA reported on four natural pearls edly from an unknown Trochoidea that also reportedly formed ranging from 5.72 to 12.40 ct that were (turban snail) species (figure 18, within Spondylus (thorny) oys- reportedly from a Spondylus (thorny right). The specimen, which meas- ters. Field of view 7.9 mm. oyster) species. These interesting non- ured approximately 27 × 19 × 12 mm nacreous pearls showed porcelaneous and weighed 39.30 ct, had a cream surfaces with unique bluish flame color, high luster, and strong orient. structures. Another even larger natu- Its smooth surface showed a unique ral pearl, also reportedly from a wavy pattern. Previously GIA re- Spondylus species, was recently sub- ported on a natural pearl from the mitted to the New York laboratory for turban snail species Astraea undosa identification. This pearl measured ap- that also showed high luster and proximately 24 × 16 mm and weighed strong iridescent colors, with an un- 42.96 ct (figure 18, left). It was formed dulating wave-like pattern (Winter in an attractive drop shape with a ho- 2003 GNI, pp. 332–334). Both pearls mogeneous yellow-brown bodycolor, share many common characteristics,

436 LAB NOTES GEMS & GEMOLOGY WINTER 2015 exact origin, these beautiful large nat- ural pearls prove just how wonderful Mother Nature is at creating spectac- ular wonders of great variety and eye- pleasing form. Chunhui Zhou and Joyce Wing Yan Ho

Two Large CVD-Grown SYNTHETIC DIAMONDS Tested The quality and size of near-colorless and colorless synthetic diamonds grown by chemical vapor deposition (CVD) have rapidly improved in recent years due to advances in growth tech- niques and the introduction of post- growth decolorizing treatments. Figure 20. The I-color 3.23 ct round on the left (9.59–9.61 × 5.83 mm) and Near-colorless CVD synthetics have H-color 2.51 ct round on the right (8.54–8.56 × 5.43 mm) are the largest now passed the three-carat threshold. CVD synthetic diamonds GIA has tested. In September 2015, a 3.09 ct sample (I color, VS clarity) of unknown prove- 2 nance was submitted to HRD Antwerp (www.hrdantwerp.com/en/news/ high-order interference colors when with dislocation bundles that fluo- hrd-antwerp-recently-examined-a-309- viewed under cross-polarized light resced violet-blue (figure 23), fol- ct-cvd-lab-grown-diamon). This was (figure 22), indicating high levels of lowed by weak greenish blue preceded by Pure Grown Diamonds’ strain. phosphorescence. Both samples were announcement of a 3.04 ct synthetic (I The synthetics showed weak or- characterized by a layered growth color, SI clarity) in December 2014 ange fluorescence to conventional structure, suggesting that the crystals 1 (www.businesswire.com/news/ short-wave UV and were inert to were grown using a multi-step tech- home/20141229005491/en/ADDING- long-wave UV radiation. Exposure to nique to maximize their volume. The MULTIMEDIA-Worlds-Largest-Labo- the deep UV radiation (< 230 nm) of sharp boundaries between the differ- ratory-Pure-Grown#.VOtnbS63raQ). the DiamondView revealed an overall ent growth layers are a result of GIA’s New York laboratory re- strong red-pink fluorescence attrib- changes in the fluorescent impurity cently tested two large CVD synthetic uted to nitrogen-vacancy centers uptake during the starting, stopping, diamonds (figure 20) submitted for grading services. These synthetics, weighing 2.51 and 3.23 ct, are the Figure 21. Left: These pinpoint inclusions were observed in the 2.51 ct syn- largest CVD-grown diamonds GIA thetic diamond. Right: A small black inclusion measuring approximately has examined to date. The results of 125 µm was observed in the 3.23 ct sample. Field of view 4.72 mm (left) the examination underscore the con- and 6.27 mm (right). tinued improvements in CVD syn- thetic diamonds. The 2.51 and 3.23 ct round bril- liants received H and I color grades, respectively. Microscopic examina- tion revealed pinpoint and black in- clusions in both, while small fractures along the girdle were only observed in the 2.51 ct round (figure 21). The 3.23 ct synthetic contained a small black inclusion measuring approximately 125 µm. As a result, SI and VS clarity 1 2 grades were given to the 2.51 and 3.23 ct samples, respectively. Both re- vealed irregular stress patterns with 1000 μm 1000 μm

LAB NOTES GEMS & GEMOLOGY WINTER 2015 437 thetic material (again, see Martineau et al., 2004). Photoluminescence (PL) spectra acquired with 514 nm laser excita- tion at liquid-nitrogen temperature revealed a doublet at 596/597 nm, nitrogen-vacancy centers at 575 [NV]0 and 637 [NV]– nm, and [SiV]– at 736.6/736.9 nm for both samples, with the [NV]0/– luminescence domi- nating. The strength of the [NV]0/– 1000 μm 1000 μm centers was consistent with the red- Figure 22. Irregular stress patterns were observed under the microscope pink fluorescence colors (figure 23). with cross-polarized light. Both the 2.51 ct (left) and 3.23 ct (right) syn- Although the 596/597 nm doublet is thetic diamonds showed high-order interference colors. Field of view 5.76 not thought to arise from the same mm and 6.27 mm, respectively. center as the 596 nm feature seen in the absorption spectrum of the 3.23 ct sample, it has only been detected in CVD synthetics, thus revealing the and restarting of growth. These im- diamonds from Gemesis Corp.,” samples’ CVD origin (Martineau et ages clearly revealed that at least five Summer 2012 G&G, pp. 80–97) but is al., 2004). The doublet also indicated growth layers were applied to pro- rarely observed in natural diamonds, that the samples had not undergone duce these large crystals. The pat- especially using absorption methods. post-growth HPHT (high-pressure, terns suggest that the table of the The 596 nm feature is particularly high-temperature) processing to im- 2.51 ct sample was cut parallel to the useful for identification purposes, as prove their color, as the treatment growth layers, while the table of the it has only been reported in CVD syn- would have removed this feature. 3.23 ct synthetic was cut at an angle to the growth layers. The dislocation bundles are seen to propagate through Figure 23. DiamondView imaging of both samples revealed strong red- the different growth layers. The for- pink fluorescence superimposed with dislocation patterns that fluoresced mation of the two blue bands of violet-blue. A layered growth structure indicating start-stop growth was highly concentrated dislocations clearly observed on the pavilion of both. The orientation of the layers re- crossing the table of the 2.51 ct spec- veals that the 2.51 ct sample (top) was cut with its table approximately imen is not understood. parallel to the growth plane, whereas the layers intersect the table facet in Infrared absorption spectroscopy the 3.23 ct sample (bottom). in the mid-IR range (6000–400 cm–1) showed no major nitrogen-related ab- sorption in the one-phonon region, which classified both samples as type IIa. No hydrogen-related defects were detected, either. UV-Vis-NIR absorp- tion spectra collected at liquid-nitro- gen temperature revealed a smooth increase in absorption from the in- frared region to the high-energy end of the spectrum, with a 737 nm peak in both samples and a small absorption peak at 596 nm in the 3.23 ct syn- thetic. The 737 nm peak is an unre- solved doublet at 736.6/736.9 nm attributed to [SiV]–. This center is often inadvertently introduced during CVD growth (P. Martineau et al., “Identification of synthetic diamond grown using chemical vapor deposi- tion (CVD),” Spring 2004 G&G, pp. 2–25; W. Wang et al., “CVD synthetic

438 LAB NOTES GEMS & GEMOLOGY WINTER 2015 139). The presence of Brazil-law twin- ning and certain inclusions, such as tourmaline or golden rutile needles, can be used to distinguish natural from synthetic quartz. But high-quality quartz, whether of natural or synthetic origin, typically has no inclusions or twinning. In this case, standard gemo- logical testing may not be able to iden- tify the origin. Advanced instruments, including infrared absorption spec- troscopy (S. Karampelas et al., “An up- [SiV]– luminescence [SiV]– luminescence date in the separation of natural from lowest highest highest lowest synthetic amethyst,” Bulletin of the Geological Society of Greece, 2007, pp. Figure 24. PL [SiV]– silicon distribution maps were collected with 532 nm 805–814) and LA-ICP-MS are consid- laser excitation. Left: Less luminescence from [SiV]– centers is observed in ered useful tools for separating natural two broad bands on the 2.51 ct sample. Right: More intense [SiV]– lumi- from synthetic material from material nescence is found at the diamond layer boundaries in the 3.23 ct sample. with synthetic origins (C.M. Breeding, “Using LA-ICP-MS analysis for the separation of natural and synthetic amethyst and citrine,” GIA News The distribution of [SiV]– centers cant improvement in CVD growth. from Research, 2009, www.gia.edu/ was investigated through PL mapping Using advanced spectroscopic and gia-news-research-nr73109a). of the 736.6/736.9 nm doublet at liquid- fluorescence imaging technologies, it The Bangkok lab recently exam- nitrogen temperature using 532 nm is nevertheless possible to detect low ined a high-clarity, transparent, near- laser excitation (figure 24). The distri- concentrations of impurity centers, colorless bangle (figure 25). Standard bution was different between the two allowing conclusive determination gemological testing revealed a spot RI samples, forming patterns that corre- of these samples’ synthetic origin. of 1.54 and an SG of 2.65, consistent sponded directly with their Diamond- GIA is monitoring the development with quartz. Magnification revealed View images (again, see figure 23). For of laboratory-grown diamonds and irregular two-phase inclusions (figure the 2.51 ct sample, the [SiV]– lumines- conducting research to ensure that we 26). These inclusions are more likely cence decreased along the bands with can continue identifying every single to be present in natural quartz than in higher concentrations of dislocation synthetic diamond. bundles. This may indicate that there Caitlin Dieck, Lorne Loudin, and – are fewer [SiV] centers in this region, Ulrika D’Haenens-Johansson or an increased concentration of de- Figure 25. A synthetic rock crys- fects (either structural or impurity- tal quartz bangle measuring ap- based) that effectively quench the proximately 80 × 22 × 10 mm. [SiV]– luminescence. Where the growth SYNTHETIC ROCK CRYSTAL layers intersect the table in the 3.23 ct QUARTZ Bangle with sample, the [SiV]– luminescence ap- Unusual Inclusions peared to be highest at the start of a Synthetic quartz is grown by the hy- layer’s growth, decreasing as the drothermal technique, which can pro- growth progressed. This could mean duce large single crystals of high that the concentration of silicon in the quality (K. Byrappa and M. Yoshimura, growth gas fell over time, or that the Handbook of Hydrothermal Technol- concentration of defects that may ogy: A Technology for Crystal Growth quench the [SiV]– luminescence in- and Material Processing, William An- creased during growth. Notably, the drew Publishing, 2001). This process, concentration of dislocations increased widely used in the jewelry trade, has as growth progressed. led to difficulty in separating synthetic Analysis of these two large samples quartz from its natural counterpart (R. demonstrates that high-quality CVD Crowningshield et al., “A simple pro- synthetic diamonds can be produced cedure to separate natural from syn- even without post-growth decolorizing thetic amethyst on the basis of HPHT treatment, marking a signifi- twinning,” Fall 1986 G&G, pp. 130–

LAB NOTES GEMS & GEMOLOGY WINTER 2015 439 unlike that of natural rock crystal quartz. The characteristic IR absorp- tions of natural rock crystal quartz oc- curred at 3379, 3483, and 3595 cm–1. These features are never seen in syn- thetic rock crystal quartz. The IR spectrum of the bangle showed ab- sorption peaks at 3610, 3585, 3431, 3294, and 3194 cm–1 (figure 27), which Figure 26. Irregular two-phase inclusions seen in the bangle using dark- matches the IR absorption features of field illumination (left and right) are similar to those found in natural synthetic rock crystal quartz (P. Zec- specimens but are rarely found in hydrothermal synthetic quartz. Field of chini and M. Smaali, “Identification view 4.1 mm. de l’origine naturelle ou artificielle des quartz,” Revue de Gemmologie, No. 138/139, 1999, pp. 74–80). The IR hydrothermal synthetic quartz, which breadcrumb inclusions. This bangle spectrum confirmed that this mate- typically shows nail-head spicule and also gave an IR absorption spectrum rial was grown by hydrothermal methods. Large transparent colorless quartz Figure 27. Infrared spectra of the synthetic rock crystal quartz bangle and can be found in natural and synthetic a 17.50 ct natural rock crystal quartz faceted bead show different absorp- forms, but synthetic quartz is usually tion patterns. The characteristic absorptions of natural rock crystal quartz seen as a flat crystal. This bangle is an –1 at 3379, 3483, and 3595 cm are never seen in synthetic rock crystal interesting example of large, high- quartz. The bangle showed absorption peaks at 3610, 3585, 3431, 3294, clarity synthetic quartz used in jew- –1 and 3194 cm , matching the IR absorption of synthetic rock crystal elry. The presence of the irregular quartz. two-phase inclusions in this example serves as an important reminder that natural and synthetic quartz can IR SPECTRA show a similar appearance and con- 2 tain internal inclusion features that Natural are identical. 3483 Synthetic 1.8 " Nattida Ng-Pooresatien " 3379 11" ,, 1.6 I\ I\ I I ,,../ \ 3585 : \ ,',3431 ../ \ 3294 ,''' \.' \ 3194 1.4 I 3595 ....__ _ -----_, 1.2 ------

3610 1 PHOTO CREDITS: Jian Xin (Jae) Liao—1, 7, 20; Yixin (Jessie) ABSORBANCE (ARB. UNITS) ABSORBANCE Zhou— 2; Sood Oil (Judy) Chia—4, 13, 18; 0.8 Kyaw Soe Moe—5, 6; Masumi Saito—9, 10; Joyce Wing Yan Ho—14, 19; Caitlin Dieck— 0.6 21, 22, and 23; Lorne Loudin—24; Nuttapol 3700 3600 3500 3400 3300 3200 3100 3000 Kitdee—25; Nattida Ng-Pooresatien—26. WAVENUMBER (cm–1)

440 LAB NOTES GEMS & GEMOLOGY WINTER 2015