LAB NOTES GEMS & GEMOLOGY SPRING 2011 49

DIAMOND

Large HPHT-Treated Cape DiamondSince the early 2000s, high-pressure,high-temperature (HPHT) treatmenthas been used extensively to improvethe color of diamonds. In the earlystages, the typical starting material wasbrown type IIa diamond, which wasprocessed to achieve a colorless to near-colorless stone. In recent years, wehave also seen brown type IaB dia-monds HPHT-treated to near-colorless(J. Van Royen et al., “HPHT treatmentof type IaB brown diamonds,” Fall 2006G&G, pp. 86–87). The treatment canalso change the bodycolor of coloreddiamonds, such as gray type IIb stonesthat are altered to blue. On rare occa-sions, the GIA Laboratory has seenlight yellow cape diamonds HPHT -treated to vivid yellow.

The New York lab recentlyreceived a 28.65 ct brownish yellow-ish orange emerald-cut diamond (fig-ure 1) for grading. Microscopic exami-nation revealed few inclusions, andthe stone showed a good polish exceptfor one facet with a frosted surface,which suggested HPHT treatment(figure 2). The diamond was inert toboth long- and short-wave UV radia-tion. Infrared spectroscopy revealedthat it was type Ia with a spectral pat-

tern typical of cape diamonds, whichwas inconsistent with the brownishorange color. The UV-Vis absorptionspectrum, however, did not show acape spectrum. Instead, we observedan increase in absorption from 700nm to higher energies (attributed toisolated nitrogen) and a weak absorp-tion from the H2 optical center (zero-phonon line at 986.2 nm).

These gemological and spectro-scopic properties indicated that thislarge brownish yellowish orange dia-mond was HPHT treated. The startingmaterial probably had a light yellow orbrownish yellow bodycolor. Instead ofbecoming intense yellow, HPHTtreatment produced a strong yellowishorange hue with a brownish modifier,

which could be attributed to a rela-tively high concentration of isolatednitrogen as well as the size of thestone.

Jason Darley

A Very Large Colorless HPHT-Treated DiamondOver the past year, the laboratory hasobserved an influx of large HPHT-treated diamonds, both type I andtype II (see Lab Notes: Spring 2010,pp. 50–51; Winter 2010, p. 298; andthe previous entry in this issue). Thistrend has continued in 2011.

Among the HPHT-annealed dia-monds we have identified recently,one was exceptional. This cushion-cut diamond weighed 38.59 ct (24.37× 18.69 × 10.22 mm; figure 3) and wasgraded F color with a clarity of VVS1.Microscopic examination revealedinternal graining in a few orienta-tions, and strong internal strain wasseen with crossed polarizers. Such fea-

Figure 1. This 28.65 ct FancyDeep brownish yellowish orangediamond is HPHT treated. Thestarting material was probably atypical cape diamond with lightyellow or brownish yellow color.

© 2011 Gemological Institute of America

GEMS & GEMOLOGY, Vol. 47, No. 1, pp. 49–55.

Editors’ note: All items were written by staffmembers of the GIA Laboratory.

EDITORS

Thomas M. Moses Shane F. McClure | GIA Laboratory

Figure 2. The diamond in figure 1had a frosted surface along thegirdle, a good indication of HPHTtreatment. Magnified 40×.

50 LAB NOTES GEMS & GEMOLOGY SPRING 2011

tures are common in HPHT-treatedtype IIa diamonds (T. M. Moses et al.,“Observations on GE-processed dia-monds: A photographic record,” Fall1999 G&G, pp. 14–22).

The IR absorption spectrum re -vealed a typical type IIa diamond, withno detectable nitrogen- or hydrogen-related features. The UV-Vis spectrumalso showed no isolated nitrogen-relat-ed absorptions. However, photolumi-nescence spectroscopy collected at liq-uid-nitrogen temperature with laserexcitations of varying wavelength con-firmed HPHT annealing, consistentwith the graining and strain patternsseen with the microscope.

This is one of the largest HPHT-treated diamonds the GIA Laboratoryhas ever identified. Treating diamondsthis size is risky, and we suspect thatnot all facilities have the equipment toanneal them, as the capsule normallyused in HPHT presses will not accom-modate such a large stone. It is alsopossible that such diamonds takelonger to process.

Gem diamonds of this size andquality are extremely rare. The increas-ing number of large HPHT-treated dia-monds seen in the laboratory under-scores the importance of proper disclo-sure and reliable gem identification.

Wuyi Wang and Tom Moses

Thermoluminescence from Type IaB DiamondsThe luminescence properties of dia-mond are widely documented in thescientific literature. Analysis of fluo-rescence, phosphorescence, cathodolu-minescence, and photoluminescence(PL) reactions has proven extremelyvaluable to gemological laboratories inidentifying natural, lab-grown, andcolor-treated diamonds. Thermo lumi -nescence (TL), the reemission of storedenergy as light in response to heating,has also been observed in diamond,though its value to gemologists hasbeen limited at best.

During PL testing of near-color-less diamonds in the Carlsbad labora-tory, we observed an interesting TLresponse from certain stones. Afterexposure to 325 nm laser excitationwhile cooled to liquid-nitrogen tem-perature (~77 K), many pure type IaBdiamonds briefly luminesced whenthey were removed from the cryo-genic vessel and allowed to warm toroom temperature (figure 4). We didnot notice this behavior in diamondsof other types observed under thesame conditions. Pure type IaB dia-monds are dominated by B-aggregatednitrogen impurities (~1175 cm−1 inFTIR spectra; figure 5) and are rela-tively uncommon among nitrogen-containing diamonds. Their observed

TL emissions were short-lived (<2seconds), mostly blue, and variedfrom strong to very weak. A few sam-ples showed green emission.

To determine the lattice defectresponsible for the luminescence, wemeasured the TL emission using aportable CCD spectrometer. The dia-monds showing blue TL displayed abroad luminescence band from ~410to 510 nm. PL spectra collected fromthe same stones using 325 nm laserexcitation showed a very strong N3defect (415 nm), which is likely thecause of the blue TL emission (figure6). One diamond displaying green TLhad a luminescence band from ~490to 550 nm, which we attributed to H3defects (503.2 nm) recorded in the PLspectrum of the sample.

While the TL behavior is apparent-ly restricted to nearly pure type IaBdiamonds, the reason for this remainsunclear. The B-aggregate of nitrogen isassociated with lattice vacancies thatmay somehow play a role. Addi -tionally, it is well known that A-aggre-gated nitrogen impurities tend toquench luminescence. We did noticethat as the A-aggregate became moreabundant, the TL emission disap-peared, even in stones with high con-centrations of B-aggregates. Whilethere is no obvious explanation for thelink between this TL behavior andpure type IaB diamonds, the lumines-cent effect is a fascinating byproductof laboratory testing.

David Nelson and Christopher M. Breeding

Two Diamonds Cut to Exhibit InclusionsThe New York lab recently observedtwo striking examples of hydrogen-and etch-related features in diamondsthat had been manufactured to high-light their inclusions. Hydrogen-relat-ed features often take the form of well-defined symmetrical clouds that areusually dark-colored or gray (W. Wangand W. Mayerson, “Sym metricalclouds in diamond—The hydrogenconnection,” Journal of Gemmology,Vol. 28, No. 3, 2002, pp. 143–152).

Figure 4. This colorless type IaBdiamond (~0.75 ct) was cooled ina liquid-nitrogen bath during 325nm laser PL analysis. When thestone was removed and warmedto room temperature, it brieflydisplayed a blue thermolumines-cence emission.

Figure 3. This 38.59 ct cushion-cut diamond proved to be HPHTtreated.

LAB NOTES GEMS & GEMOLOGY SPRING 2011 51

Such clouds are often obscured by adiamond’s faceting, but that was notthe case with these specimens.

The first, a 1.05 ct Fancy gray–greenish yellow octahedron (figure 7),had been polished to preserve the orig-inal rough shape. Clearly visible in theinterior was a cloud with an elaboratestructure that was well-aligned withthe polished faces. Such formationscould be related to octahedral growthand variations in the crystallizationenvironment. Viewed through the largetriangular facets, the cloud resembled aStar of David hexagram.

The other diamond, a 4.51 ctFancy greenish yellow-brown roundbrilliant (figure 8), contained a hydro-gen cloud composed of six roughlyoval-shaped arms aligned to a centralpoint and extending along the [100]axes. Even more conspicuous werebundles of needle-like etch channelsthat converged in the diamond’s cen-ter (see also Fall 2009 Lab Notes, pp.209–210). These channels result fromcorrosive fluids in the magma thattransport diamonds from deep withinthe earth to near-surface environ-ments. Under certain conditions, the

fluids can dissolve deep into the inte-rior of the diamond, following direc-tions of weakness in the crystal struc-ture. It is very common to see etchchannels along the [111] directions, asin this example. These channels had abrown color from natural radiationstaining.

The varying appearance of hydro-gen clouds is not fully understood.One possible explanation is that acloud tends to be concentrated in the{100} growth sector due to the dia-mond’s higher surface energy duringgrowth. If growth paused for any rea-son, the cloud could have spread alongthe crystal edges, forming an octahe-dral outline once growth resumed.

Rather than follow the conven-tional approach to cutting, whichseeks to minimize inclusions for thesake of market value, these unusualdiamonds accentuated the naturalbeauty of their growth features, mak-ing them truly one-of-a-kind.

Jon Neal, Jason Darley, and Vinny Cracco

WAVELENGTH (nm)

400 450 500 550 600 650 700

PL SPECTRUM

INTE

NSI

TY

415N3

WAVENUMBER (cm-1)

4000 3500 3000 2500 2000 1500 1000

FTIR ABSORPTION SPECTRUM

0

1

2

3

1175

AB

SOR

BAN

CE

Figure 5. FTIR spectroscopy demonstrated that the diamonds showing TLemission were nearly pure type IaB, as indicated by the band at 1175 cm−1.

Figure 6. PL analysis of type IaB diamonds with blue TL emissionshowed a prominent N3 defect (415 nm peak), which is likely thecause of the TL behavior.

52 LAB NOTES GEMS & GEMOLOGY SPRING 2011

HALITESubmitted for Identification A 13.25 g near-colorless piece of roughwas recently submitted to the Carls -bad laboratory for identification (fig-ure 9). Initial examination showed arounded surface with one large flatside that was obviously a cleavage, asits stepped appearance in some areasindicated it had been broken ratherthan sawn. Dissolution tubes extend-ed into the stone in three directions atright angles.

The RI of the cleavage surface wasaround 1.55, though the unpolishedsurface yielded a rather indistinctreading. The optic character, observedwith a polariscope, was singly refrac-tive. The specimen fluoresced weakyellow to long-wave UV radiation andwas inert to short-wave UV. Given thedissolved appearance of the surface,the author was hesitant to measurethe sample’s hydrostatic specific grav-ity. Water-soluble minerals have beenused as gems (e.g., the hanksitedescribed in the Spring 2010 GemNews International [GNI], pp. 60–61),and immersing such a specimenmight cause damage.

While there were no obviousexternal clues to the morphology ofthe specimen other than its perfectcleavage, microscopic examinationproved more revealing. With magnifi-cation, numerous planes of fluid-filled cubic negative crystals werevisible (figure 10, left). The cubiccrystal system was consistent withthe singly refractive character. Mostof the negative crystals contained abrown to colorless liquid with a gascomponent, but a few contained agreen fluid with several daughtercrystals (figure 10, right). Both typesof fluid inclusions were indicative ofa natural material.

Further testing with energy-dis-persive X-ray fluorescence (EDXRF)spectroscopy indicated that the majorelements were sodium and chlorine.The ionic combination of these twoelements is familiar to us as halite, orcommon table salt. Raman analysisconfirmed this identification.

Although halite is not rare ordurable enough to be considered a gemmaterial, this proved to be an interest-ing exercise in identification. Becausethe surface provided so little crystallo-graphic information, most of the cluescould only be gathered from micro-scopic features. A solid foundation incrystallography and micros copy isessential for any gemologist, who maybe called on to identify even non-gem-related materials.

Nathan Renfro

Three Similar-Appearing GreenStones: JADEITE, OMPHACITE,and HYDROGROSSULARThe New York laboratory recentlyreceived several green cabochons foridentification over the period of a fewdays (e.g., figure 11). They all had a sat-urated green color, and microscopicobservation revealed similar micro-crystalline textures. Observation witha dichroscope showed very weak or nopleochroism, which is common forfine-textured aggregates. In the desk-model spectroscope, all of the cabo-chons displayed chromium lines near690 nm, and all but one also had a linenear 437 nm, as seen in jadeite andomphacite. The samples were inert tolong- and short-wave UV radiation.Their SG values, however, varied from2.90 to 3.34. In addition, all but one ofthe cabochons had refractive indicesof 1.66–1.68—typical values forjadeite and omphacite—while theother stone (also with the highest SGvalue) had an RI of 1.72.

Raman spectroscopy identifiedthe stone with the highest RI and SGvalues as hydrogrossular (hibschite).This identification was further sup-ported by infrared spectroscopy, basedon distinct hydroxyl absorption bandsin the 4000–3000 cm−1 region.EDXRF spectroscopy indicated majoramounts of calcium, aluminum, andsilicon, with minor chromium, con-sistent with hydrogrossular’s formulaof Ca3Al2(SiO4)3–x(OH)4x (x = 0.2–1.5)

Figure 7. This 1.05 ct Fancy gray–greenish yellow diamond containsa cloud with an octahedral struc-ture that matches that of the pol-ished faces.

Figure 8. In this 4.51 ct Fancygreenish yellow-brown roundbrilliant, bundles of needle-likeetch channels converge at thecenter, dividing the six oval-shaped clouds (only four of whichare visible here).

Figure 9. The rounded surface ofthis 13.25 g piece of halite was theresult of dissolution. The cleavageplane indicates the specimen hadbeen cleaved after dissolution.

LAB NOTES GEMS & GEMOLOGY SPRING 2011 53

and the stone’s green color. Hydro -grossular occurs in green colors whentrace amounts of chromium are pres-ent, and variations in hydroxyl con-tent cause differences in physicalproperties such as RI and SG (W. A.Deer et al., Rock-Forming Minerals—Orthosilicates, Vol. 1A, 2nd ed.,Long man Group Ltd., London, 1982).

The other cabochons were identi-fied as jadeite or omphacite, using thesame techniques. Ompha cite [(Ca,Na)(Mg,Fe,Al)Si2O6] is a clinopyroxenethat forms a solid solution withjadeite (NaAlSi2O6). Both mineralshave similar properties—such as over-lapping RI values—and they were dif-ferentiated by Raman spectroscopy.Further confirmation was provided byEDXRF, which revealed the presenceof Ca and Fe in omphacite, and theabsence of these elements in jadeite.

Positive identification of jadeitecan be difficult because other mineralsalso exhibit similar fine aggregate tex-ture, SG and RI ranges, hardness, UVreaction (if not impregnated), and/orchromium-related UV-Vis absorption

bands; amphibole (nephrite) and ser-pentine-group minerals are some ofthe better-known examples. Properidentification requires careful observa-tion and testing.

Ren Lu

Beryllium- and Tungsten-BearingSAPPHIRES from AfghanistanIn March 2010, the Bangkok laborato-ry received a rough parcel of 175 bluesapphires reportedly from a relativelynew deposit near the lapis lazulimines in the Kokcha Valley ofAfghanistan’s Badakhshan Province.The pieces ranged from ~0.2 to 4 g (fig-ure 12), and about half the parcel wasgem quality. During a trip to Afghani -stan in July 2010 (see Winter 2010GNI, pp. 319–320), one of us (VP)obtained six additional samples said tobe from this deposit, consisting of bluesapphires on a matrix of bluish greenand yellowish brown crystals (identi-fied as dravite and phlogopite byRaman and laser ablation–inductively

coupled plasma–mass spectrometry[LA-ICP-MS] analysis, respectively).

Of the 181 samples, most hadstrong hexagonal blue color zoningsurrounding a yellow core that dis-played a six-rayed star pattern whenviewed with transmitted light (figure13). Common inclusions were nega-tive crystals (sometimes associatedwith healed fissures), corroded zirconcrystals, twin planes, and crystals ofcorundum. Most of the sapphires weresector zoned with colorless areas asso-ciated with the basal pinacoid.

EDXRF analysis detected iron, gal-lium, vanadium, and surprisingly,tungsten (an element typically associ-ated with synthetics). LA-ICP-MSshowed similar amounts of galliumand vanadium in both the blue and col-orless areas. However, the colorlessareas were higher in magnesium andlower in iron, while titanium wasnearly absent. Significant levels ofberyllium (up to 20 ppma), as well asniobium, tin, tantalum, zirconium,hafnium, and tungsten (30–700 ppma)were found in the colorless areas butnot in the blue portions. Though notcommon, beryllium (in associationwith niobium and tantalum) has beenreported in some untreated blue sap-phires from Madagascar (V. Pardieu,“Beryllium discovered in unheatedsapphires,” InColor, Fall-Winter 2007-2008, p. 41) and Tasmania (B. M.McGee, “Characteristics and origin ofthe Weldborough sapphire, NE Tas -mania,” bachelor’s thesis, School ofEarth Sciences, University of Tas -mania, 2005).

UV-Vis spectroscopy showedstrong absorptions at 580 and 700 nm(o-ray) and ~700 nm (e-ray) that aretypical of metamorphic/metasomat-ic-type blue sapphires. Very weakiron-related absorptions were visibleat 377, 388, and 450 nm, and the spec-trum cutoff tended to be very low(around 300 nm). The FTIR spectra(figure 14) showed strong absorptionbetween 3700 and 3100 cm−1 (proba-bly due to molecular water) as well asfeatures related to diaspore (lines at2120 and 1990 cm−1 and broad bandsaround 3020 and 2880 cm−1) and mica

Figure 10. The cubic habit of these fluid-filled negative crystals revealsthe halite’s crystal structure (left, magnified 60×). A few of them hosted agreen fluid and multiple daughter crystals (right, magnified 100×).

Figure 11. These three similar-looking stones were identified (left to right)as jadeite (23.90 ct), omphacite (8.12 ct), and hydrogrossular (13.90 ct).

(lines in the ~3700–3620 cm−1 region)in most samples. A band at 3163 cm−1

was also observed in most of the sap-phires, along with some unusualabsorptions: a broad band at 3428 cm−1,a sharp feature at 3387 cm−1, and aseries of four broad bands at ~4450,4306, 4200, and 4100 cm−1.

The presence of such distinctivechemical and spectral features in thesesapphires, combined with their report-ed origin near the historic Afghan lapismines, makes them a very interestingaddition to the marketplace.

Vincent Pardieu, Sudarat Saeseaw,Kamolwan Thirangoon, and

Pantaree Lomthong

Aggregate of Black SYNTHETIC MOISSANITE andCrystalline SILICONThe Carlsbad laboratory recentlyreceived a 1.35 ct black submetallicround brilliant for an identificationand origin report. It had an SG of3.06, an over-the-limit RI, and wasopaque to strong fiber-optic light.These properties suggested syntheticmoissanite, although the SG waslower than the 3.22 previouslyreported for this material (K. Nassauet al., “Synthetic moissanite: A newdiamond simulant,” Win ter 1997G&G, pp. 260–275). Curiously, thesample displayed a granular structurein reflected light, which seemed to bean intergrowth of a higher-luster metallic material with a duller, dark-er matrix (figure 15). Raman spec-troscopy identified the matrix as syn-thetic moissanite and the interstitialmetallic material as crystalline sili-con. The abundance of silicon in thissample accounted for its low SG.

Silicon inclusions in black syn-

thetic moissanite were describedrecently by Haibo et al. (Winter 2009GNI, p. 308), though the intergrowthin this stone was much more exten-sive than the isolated silicon blebs inthat report. Like the samples exam-ined by Haibo et al., though, thisblack synthetic moissanite appearedto be a product of the physical vaportransport (PVT) technique. Siliconinclusions have not been reported insynthetic moissanite grown by seededsublimation, but they are known inPVT material grown in China (Z.Chen et al., “Growth of large 6H-SiCsingle crystals,” Journal of InorganicMaterials, Vol. 17, No. 4, 2002, pp.685–690).

Alethea Inns

SYNTHETIC STAR SPINELImitation of MoonstoneThe Carlsbad laboratory recentlyexamined a translucent white roundcabochon that initially appeared to be

54 LAB NOTES GEMS & GEMOLOGY SPRING 2011

Figure 13. Microscopic examina-tion of this sapphire with trans-mitted light shows hexagonal bluebands surrounding a yellow corethat displays a star pattern. Thehigh-relief inclusion in the core isa negative crystal. Magnified 40×.

Figure 12. These sapphire crystals(~0.2–4 g) are reportedly fromAfghanistan’s BadakhshanProvince. Most are tabularprisms, with a colorless area (thatappears grayish here) on the topand bottom of each crystal.

Figure 14. These FTIR spectra of a Badakhshan sapphire (sample668563702, 1.35 ct and ~4 mm thick) reveal strong absorption between3700 and 3100 cm−1 (probably due to molecular water), as well as mica-related bands and some unusual features.

WAVENUMBER (cm-1)

4500 4300 4100 3900 3700 3500 3300 3100

FTIR ABSORPTION SPECTRA

5

6

7

4450

AB

SOR

PTIO

N C

OEF

FIC

IEN

T

4306

42004100

3710

3648 3387

3163

3428

3245

e-ray

o-ray

LAB NOTES GEMS & GEMOLOGY SPRING 2011 55

a moonstone (figure 16). The sam-pleshowed a pronounced bluish adu-larescence in diffused lighting. Whenviewed with a direct light source suchas fiber-optic illumination, however,it displayed a pronounced star (figure16, right). This star contained fourpairs of rays, a somewhat unusualconfiguration.

Gemological testing revealed prop-erties consistent with syntheticspinel, including a spot RI reading of1.72 and strong green fluorescence toshort-wave UV radiation. Micro scopicexamination uncovered a dense net-work of dislocation stringers, orientedcrystallographically throughout thegem (figure 17). In cross-polarizedlight, these dislocation networks dis-played considerable strain. Alsoobserved with magnification was ablue metallic coating on the back of

the cabochon. In reflected light, therewere obvious areas where the coatinghad chipped off (figure 18). This coat-ing was apparently added to create aneffect resembling the blue adulares-cence seen in moonstone.

Because the mounting preventedadditional tests such as specific gravi-ty measurement, advanced testingwas needed to confirm the identity ofthis cabochon. EDXRF spectroscopyshowed Al and Mg as the only majorelements, consistent with the expect-ed composition of spinel. Minor traceelements were iron, titanium, andchromium.

The crystallographically orienteddense network of dislocations is thepresumed source of the asterism, andthe four-rayed pattern is consistentwith the synthetic spinel’s cubic crys-tal structure. This contributor had

never seen a synthetic star spinel,much less one that imitated moon-stone. Given moonstone’s wide avail-ability and typically modest price, itis unlikely that there are many suchspecimens in the market. Never -theless, buyers should be aware thatimitations can occur at any pricelevel. And even though this cabochonproved to be a synthetic imitation, itcan be appreciated as an interestingspecimen in its own right.

Nathan Renfro

Figure 15. Reflected light shows the aggregate structure of the syntheticmoissanite (which appears dark gray here, with darker pits) and thebright-reflecting crystalline silicon. Magnified 30× (left) and 112× (right).

Figure 16. This ~5 ct synthetic star spinel made a convincing moon-stone imitation in diffused lighting, but in direct lighting it showeda pronounced star.

Figure 17. Dense stringer-like dislo-cations throughout the syntheticstar spinel, viewed here at 60× mag-nification, produced the asterism.

PHOTO CREDITSJian Xin (Jae) Liao—1, 7, 8, and 11; JasonDarley—2; Sood Oil “Judy” Chia—3;Robert Weldon—4; Robinson McMurtry—9 and 16 (left); Nathan Renfro—10, 17, and18; Vincent Pardieu—12 and 13; AletheaInns—15; Don Mengason—16 (right).

Figure 18. Defects in the metallicblue coating on the back of the syn-thetic star spinel were obvious inreflected light at 100× magnification.