134 LAB NOTES GEMS & GEMOLOGY SUMMER 2009

DIAMOND

Bicolored DiamondGIA only rarely encounters faceteddiamonds that merit two color gradesbecause of the presence of two distinctcolored areas (e.g., Winter 1989 LabNotes, p. 237). Recently, the New Yorklaboratory had the chance to examinejust such a stone, when the 1.79 ct rec-tangular step cut in figure 1 was sub-mitted for grading. The diamond wasassigned two color grades: Fancy Darkorangy brown and near-colorless, bothconfirmed to be of natural origin. Thepronounced orangy brown color wasconfined to one half of the stone; asharp boundary separated it from thenear-colorless half. Some fracturesextended across the boundary, but the(highly reflective) mineral inclusionsindicative of a natural type Ib diamondwere observed only in the orangybrown region. Both regions fluorescedmoderate blue to long-wave ultravioletradiation; however, the near-colorlessregion displayed stronger yellow fluo-rescence to short-wave UV than theorangy brown region. No phosphores-cence was observed.

Infrared absorption spectra collect-ed from the two regions also revealedclear differences. The near-colorlessregion showed a characteristic typeIaA spectrum with a very low concen-tration of nitrogen and a very weakhydrogen-related absorption at 3107cm–1. In contrast, the orangy brownsection showed the “irregular” fea-tures usually observed in natural yel-low-orange diamonds colored by thelattice defect referred to as the “480nm band” (e.g., Spring 2007 Lab

Notes, pp. 49–50), as well as traceamounts of isolated nitrogen. In addi-tion to the 3107 cm–1 peak, sharp linesat 3313, 3299, 3272, 3191, 3182, and3144 cm–1 were recorded. All theseobservations indicated that the orangybrown color was due to the 480 nmband defect and isolated nitrogen.None of these features were detectedin the infrared spectrum from thenear-colorless region.

Most natural diamonds are typeIa, with the majority of nitrogen pres-

EditorsThomas M. Moses andShane F. McClureGIA Laboratory

© 2009 Gemological Institute of America

GEMS & GEMOLOGY, Vol. 45, No. 2, pp. 134–140.

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

Figure 1. This unusual diamond(1.79 ct) proved to be a mixed-type IaA/Ib, with the two typescorresponding to the near-color-less and Fancy Dark orangybrown regions, respectively.

Figure 2. In the DiamondView,the diamond in figure 1 showedtwo distinct areas of growth,again corresponding to the differ-ent colors (near-colorless, top;orangy brown, bottom).

LAB NOTES GEMS & GEMOLOGY SUMMER 2009 135

ent as IaA aggregates. Type Ib singlysubstituted nitrogen rarely occurs innatural diamonds. When present innatural stones, it can cause an orange-yellow (“canary”) color, occasionallywith brownish or, rarely, reddishmodifiers (e.g., Fall 2008 Lab Notes,pp. 255–256). This bicolored dia-mond contained both type Ia aggre-gated nitrogen and type Ib isolatednitrogen. While it is not unusual for adiamond to contain different forms ofnitrogen aggregates, the sharply defineddistribution of these defects withrespect to the distinct color zones isunusual.

DiamondView imaging indicatedthat this stone may have crystallizedduring two different periods of growthand in two different growth environ-ments (figure 2). Distinct differences indefect configuration between the twosections also suggest that the nitrogenaggregation process after diamondcrystallization in the mantle may havebeen affected by factors (e.g., occur-rence of other lattice defects) in addi-tion to temperature and duration.

Erica Emerson, Paul Johnson,and Wai Win

“Black” Diamond with Deep Violet ColorBlack diamonds are not uncommon inthe gem trade, but naturally coloredexamples are relatively rare. Mostblack diamonds currently in the mar-ket are produced by the heating offractured diamond to high tempera-tures in a vacuum to induce graphiti-zation of the feathers and inclusions.The result is a nearly opaque stonethat contains so much graphite thatthe diamond will conduct an electriccurrent. In the past, treatmentsinvolving heavy-dose irradiation orirradiation plus annealing have alsobeen used to produce black diamondsthat are, in reality, very dark greenwhen viewed with strong fiber-opticillumination. On occasion, we haveseen other very dark colors, such asorange and blue. Naturally coloredblack diamonds typically containabundant dark inclusions (sometimes

graphite) that cause the stones toappear black when viewed face-up.Dense, dark-colored hydrogen cloudshave also been reported as a naturalcause of black color in diamonds (seeLab Notes: Fall 2008, p. 254; Spring2009, pp. 54–55).

Recently, we examined an inter-esting 0.4 ct marquise brilliant in theCarlsbad laboratory. The tone of thediamond was so dark when it wasviewed face-up that the stone wasgraded Fancy black (figure 3, top).Table-down examination in a whitetray, however, revealed that the body-color of the diamond was in fact a verydeep violet (figure 3, bottom). This isremarkable because we had not previ-ously seen a violet diamond with sucha dark tone.

The diamond’s infrared absorptionspectrum (see the G&G Data Deposi-tory at www.gia.edu/gandg) showedthat it was type Ia with very high con-centrations of nitrogen and hydrogen

impurities. As is typical of naturalhydrogen-rich violet diamonds, thestone contained shallow etch pits andcavities, and fluoresced yellow to bothlong- and short-wave UV radiation (C.van der Bogert et al., “Gray-to-blue-to-violet hydrogen-rich diamonds fromthe Argyle mine, Australia,” Spring2009 G&G, pp. 20–37).

This marquise cut represents anextremely rare type of black diamond.It was issued a “natural” color originreport.

Christopher M. Breeding andKimberly M. Rockwell

Carved Diamond CrucifixIt is not unusual to see carved dia-monds submitted to the laboratory foridentification. Over the years, theyhave come in many forms, such ascarved fish (Spring 1983 Lab Notes, p.73) or dice (Fall 1985 Lab Notes, p.172). Carved diamonds with religiousthemes have also been submitted,including one fashioned as a Hamsa,symbolizing the protective hand of thecreator (Fall 2001 Lab Notes, p. 214),and another cut in the image of theBuddha (Fall 1996 Gem News, p. 215).In reviewing our records, however, itdoes not appear that we have previous-ly examined a crucifix such as the oneshown in figure 4.

This piece consisted of a carving ofChrist on a white metal cross; theChrist figure was determined to bediamond by Raman analysis. Thegrayish appearance of the diamondwas due to numerous graphite-con-taining fractures. There was also evi-dence of the rough diamond crystal atone point on the carving, a corner of atrigon and some striations.

While many diamond carvingstoday are created using lasers, theclient stated that this crucifix hadbeen fashioned by a now-deceasedIndian master carver using just handtools. Only a skilled craftsman withexceptional patience could performthis type of carving, in this detail. Toour knowledge, this diamond crucifixis unique.

Garry Du Toit

Figure 3. This 0.4 ct diamond wasgraded Fancy black. When viewedthrough the pavilion (bottom), thestone shows deep violet color.

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Rare Type IIb Gray-Green DiamondNatural type IIb diamonds are very rare.Among those we have examined in theGIA Laboratory, only about half showeda pure blue color, with the other halfdisplaying an additional gray compo-nent due to varying levels of saturation.Two of the most famous type IIb dia-monds, the Hope and the Wittelsbach,were color graded Fancy Deep grayishblue. Occasionally, brown diamondswith type IIb characteristics have alsobeen seen (e.g., Summer 1977 LabNotes, p. 307; Winter 2008 Lab Notes,pp. 364–365). Recently, staff membersin the New York laboratory had theopportunity to examine an extremelyrare type IIb diamond for which thedominant color was green.

The 5.41 ct marquise brilliant cutin figure 5 was color graded FancyDark gray-green. With magnification,the diamond showed only minor frac-tures reaching the surface. It had noreaction to either long- or short-waveUV radiation, which is characteristicof type IIb diamonds. When examinedunder the strong short-wave UV radia-

tion of the DiamondView, it showedmoderately strong blue florescenceand weak red phosphorescence.

Infrared and photoluminescence

spectroscopy revealed features ob-served in other natural type IIb dia-monds. No evidence of artificial irradi-ation was detected. However, someunusual features were observed in theultraviolet-visible–near infrared region(see the spectrum in the G&G DataDepository at www.gia.edu/gandg). Incontrast to typical blue IIb diamonds,which often show a uniform increasein absorption from the UV toward thelower energy/longer wavelength side,this diamond displayed increasingabsorption from ~500 nm toward thehigher energy/shorter wavelength side.As a result, a transmission windowwas created from ~500 to 525 nm,leading to the dominant green hue.This increase in absorption from ~500nm to shorter wavelengths is very like-ly caused by plastic deformation of thecrystal lattice, a common feature inmany natural diamonds.

A natural type IIb diamond with adominant green hue is extremely rare.This unusual color is a result of theright combination of boron concen-tration, intensity of plastic deforma-tion, and influence of the cut style.

Paul Johnson and Jason Darley

Unconventional Diamond CutsIn March, the New York lab received anumber of diamonds with unusual andunconventional facet distributions.They ranged in shape from round andcushion to pear and rectangular, but allhad one feature in common: a fullyfaceted dome-shaped crown, witheither no table at all or only a tiny“culet”-style facet in the center of thecrown (figure 6). We were surprised tosee these experimental cuts beingapplied to fairly large diamonds, mostof them between 2 and 7 ct, as well asto diamonds of different colors.

Diamond cuts that lack a tablefacet invariably pose challenges forcalculating overall dimensions andcrown and pavilion angles, since typi-cally the table serves as the basic ref-erence plane against which theseangles are measured. The cut descrip-tion (shape and cutting style) alsobecomes more difficult, because none

Figure 5. This highly unusualFancy Dark gray-green diamond(16.54 × 9.13 × 5.87 mm) provedto be type IIb.

Figure 4. This unique crucifix (27.12 × 7.24 × 4.25 mm) consisted of a carveddiamond set on a white metal cross.

LAB NOTES GEMS & GEMOLOGY SUMMER 2009 137

of the standard terms in the GIA lexicon fully explain these designs.

We were pleasantly surprised,however, to see that a number of thestones showed a balanced contrastpattern, which is very unusual fornontraditional diamond cuts (andeven for the standard fancy cuts).When we compared one of the roundshapes with a round brilliant cut (grad-ed by GIA as “Excellent”) of the samediameter, the latter appeared darker

overall, with a less subtle contrast pat-tern. We have not analyzed the lightpath by ray tracing, but we believethat the fragmented specular reflec-tion or glare of the additional crownfacets, in combination with an effi-cient light-path migration inside thediamond, results in this brighter andmore sparkly look.

We contacted the client andlearned that this new cut has beenpatented and will be marketed as“Antwerp Twins.” The name waschosen to reflect the cut’s city of ori-gin and the fact that these diamondshave two “dome-faceted” sides (crownand pavilion), as shown in figure 7.

While unconventional cuts can bechallenging to measure, classify, andgrade, we appreciate the opportunityto view the results of this type ofinnovation.

Ronnie Geurts

Pink CVD SYNTHETIC DIAMONDGem-quality synthetic diamondsgrown by chemical vapor deposition(CVD) were introduced to the jewelrymarket several years ago, but only alimited number of stones have been

submitted to the GIA Laboratory fortesting, and those have been near-col-orless or brown (see, e.g., Lab Notes:Spring 2008, pp. 67–69; Summer 2008,pp. 158–159; Winter 2008, pp.365–367). Recently, however, we iden-tified a rare CVD synthetic diamondwith a distinct pink coloration.

This 0.54 ct cushion cut, originallysubmitted for a colored diamond grad-ing report, was graded Fancy brownishpink (figure 8). Although comparableto that seen in many natural counter-

Figure 6. The Antwerp Twins cut is used on different shapes, such as those shown here (2.27, 4.17, and 2.08 ct).Note the fully faceted crown on each diamond and the small culet-style facet in the center of the yellow oval.

Figure 8. This 0.54 ct Fancybrownish pink cushion cut (4.97× 4.90 × 2.60 mm) was identifiedas a CVD synthetic diamond.

Figure 7. This side view of the2.08 ct round-cut Antwerp Twinsdiamond in figure 6 shows theunusual “dome” faceting of thecrown and pavilion.

138 LAB NOTES GEMS & GEMOLOGY SUMMER 2009

parts, this color is rare in synthetic diamonds. The color was evenly dis-tributed throughout. With magnifica-tion, the gem displayed strong disloca-tion-related graining in a lineararrangement. Except for one black“pinpoint” (likely graphite), no otherinclusions or fractures were observed.

We detected weak orange-yellowfluorescence to both long- and short-wave UV radiation. Under the ultrashort-wave UV radiation of theDiamondView, the cushion cut dis-played strong, uniform orange-red flu-orescence, as well as moderatelystrong, evenly distributed yellowphosphorescence. We did not observethe irregularly distributed blue fluo-rescence seen in many CVD synthet-ic diamonds. In addition, the charac-teristically striated growth structureof CVD synthetics (P. Martineau etal., “Identification of synthetic dia-mond grown using chemical vapordeposition [CVD],” Spring 2004G&G, pp. 2–25; W. Wang et al.,“Latest-generation CVD-grown syn-thetic diamonds from Apollo Dia-

mond Inc.,” Winter 2007 G&G, pp.294–312) was less pronounced.

Infrared absorption spectroscopyrevealed typical type IIa features, withno detectable absorption in the one-phonon region. Noticeable featuresincluded weak but sharp absorptionsat 7804, 5219, 4888, 4767, 4648, 4587,4337, and 3123 cm–1. These absorp-tions are specific to CVD syntheticdiamonds and have been reported inother pink samples (Wang et al.,2007). Notable features in the UV-Vis-NIR absorption spectrum (collected atliquid-nitrogen temperature) includeda moderately strong broad band cen-tered at ~520 nm that is the maincause of pink coloration, a sharpabsorption doublet at 736.5/736.9 nmfrom a Si-related defect, and sharppeaks at 753.0 and 850.2 nm (figure 9).Assignment of the 753.0 and 850.2nm peaks is ambiguous, but theyhave not been reported in natural dia-monds. The color of most naturalpink diamonds is caused by a broadabsorption band centered at ~550 nm,slightly higher than the 520 nm band

in this CVD synthetic diamond. The photoluminescence (PL) spec-

trum was dominated by emissions ofN-V centers (ZPL at 574.9 nm and637.0 nm) and a Si-related defect(736.5/736.9 nm doublet). In addition,numerous weak and sharp peaks weredetected in the 460–530, 670–700,and 740–780 nm regions.

Pink CVD synthetic diamonds arerarely encountered in the gem market.Despite their many close similaritieswith natural pink diamonds, they canbe identified reliably by spectroscopicfeatures such as the H-related 3123cm–1 absorption in the infrared regionand the Si-related 736.5/736.9 nmdoublet seen with both absorption andPL spectroscopy.

Wuyi Wang

Rare Star PERIDOTCat’s-eye peridot is rare, and star peri-dot is rarer still. Only two examples ofthe latter have been reported by theGIA Laboratory (Spring 1960 High-lights at the Gem Trade Lab in LosAngeles, p. 3; Summer 1987 LabNotes, p. 106). The first was describedas having a “well-defined four-rayedstar reflected from tiny needlelike ori-ented inclusions,” the second as hav-ing a star with two strong arms andtwo weaker arms. Recently, we wereloaned for examination a 22.21 ct ovalperidot with a uniformly distinct four-rayed star (figure 10).

Standard gemological testing con-firmed the stated identity and gavethe following properties: diaphane-ity/color—transparent to semitrans-parent brownish green; spot RI—1.65;hydrostatic SG—3.32; and absorptionbands observed at 453, 477, and 497nm in the desk-model spectroscope.Despite the stone’s relatively hightransparency, examination with agemological microscope revealed thatit was filled with inclusions. “Finger-prints” and brown platelets were themost obvious internal features (figure11, left). With fiber-optic illumina-tion, oriented fine iridescent thinfilms, tiny needles, and short stringsof reflective particles were observed

Figure 9. The UV-Vis-NIR absorption spectrum of the CVD synthetic dia-mond in figure 8 displayed a moderately strong broad band centered at ~520nm (not shown), which is the main cause of the pink coloration. In the NIRregion (shown), a sharp absorption doublet at 736.5/736.9 nm from a Si-related defect was observed, along with sharp peaks at 753.0 and 850.2 nm.

LAB NOTES GEMS & GEMOLOGY SUMMER 2009 139

throughout (figure 11, right); theseabundant inclusions were the cause ofthe asterism. We performed Ramanspectroscopy in an attempt to identifythe platelets, but the spectra showedtoo much interference from the hostperidot. As many of the plateletsappeared brown in transmitted light,the possibilities include phlogopite,biotite, or even the ilmenite that wassuggested for the peridot in theSummer 1987 Lab Note.

Accurately photographing theasterism proved quite challenging. Asa result, the image in figure 10 is acomposite of two digital photos—onefocusing on the star, the other on theoutline of the cabochon.

Donna Beaton

TOURMALINE with Silver andGold Chatoyancy In the Fall 2001 Lab Notes (pp.218–219), we reported on a 1.51 ct starsapphire double cabochon that dis-played a six-rayed “silvery” star on oneside and a six-rayed “golden” star onthe opposite side. This effect was dueprimarily to color zoning and the dis-tance of the phenomenon-causinginclusions from the surface of the gem.

We recently had the opportunity

to examine a cat’s-eye tourmaline,said to be from Mozambique, thatdisplayed a similar dual-color phe-nomenon. The 5.44 ct double cabo-chon (figure 12) was loaned for exam-ination by Leon M. Agee (AgeeLapidary, Deer Park, Washington).The 12.01 × 10.59 × 5.46 mm gemdisplayed a strong silvery white eyeon one side and a deep golden browneye of almost equal intensity andsharpness on the other. When thecabochon was positioned between

two light sources and then rotated,both eyes could be made to open andclose dramatically, as would be expect-ed in a fine cat’s-eye chrysoberyl.

Microscopic examination revealedvery strong color zoning, with a gold-en brownish yellow zone positionedparallel to a near-colorless achroitelayer. The near-colorless side con-tained numerous very fine, uniformlydistributed growth tubes of the sortrequired to produce strong chatoyan-cy. Reflections from these inclusions

Figure 11. The star peridot had numerous inclusions of brown platelets (left,magnified 75×), though these could not be identified by Raman spectroscopy.Fiber-optic illumination revealed the abundant fine needles, thin films, andparticle strings (right, magnified 85×) that caused the peridot’s asterism.

Figure 10. This unusual 22.21 ctperidot displayed a distinct four-rayed star.

Figure 12. Fashioned from tourmaline reportedly mined in Mozambique,this 5.44 ct double cabochon displays silver chatoyancy on one side and agolden eye on the other.

140 LAB NOTES GEMS & GEMOLOGY SUMMER 2009

were responsible for the silvery whiteeye (figure 12, left). The growth tubesdid not extend into the brownish yel-low color-zoned area; instead this sidegained its golden chatoyancy by reflec-tions from the tubes in the near-color-less zone, which were projectedthrough the color layer (figure 12,right).

This is the first time we haveencountered a tourmaline displayingthis dual-color phenomenon. Themost logical way to set such a gemwould be in a pendant with a simplebezel, leaving both sides exposed sothat either cat’s-eye could be enjoyed.

John I. Koivula

Eljen Treated TURQUOISE In 2004, turquoise treated by a propri-etary process developed by EljenStones (Reno, Nevada) first appearedon the market. According to thetreater, Elven Jennings, his companyhas processed approximately 6 tonnesof rough material since then. In the lastthree years, about 1.4 million carats offinished goods were cut from ~1.4tonnes of treated material. Mr.Jennings claims that his proprietaryprocess transforms soft, chalkyturquoise into harder material thattakes a better polish with little or none

of the weight gain he has experiencedwith stabilized turquoise, and withoutusing any dyes or surface coatings.

We examined three rough samples(10.23–24.06 g) and five cabochons(5.93–12.62 ct; e.g., figure 13) ofturquoise treated by the Eljen processand donated to GIA by Mr. Jenningsand Dayton Simmons. The sampleswere greenish blue to blue, some withbrown matrix. The polished stones hadgood to very good luster. Standardgemological testing revealed Spot RIsranging from 1.60 to 1.62 and SG val-ues of 2.27–2.85.

The IR spectra of all the samplesresembled those of polymer-impreg-nated turquoise. We did not detectany evidence of Zachary treatment,such as the presence of abnormallyhigh concentrations of potassium,with energy-dispersive X-ray fluores-cence (EDXRF) spectroscopy. UV-Visspectroscopy showed a standardturquoise spectrum and no evidenceof dye. When exposed to long-waveUV radiation, all the samples fluo-resced weak-to-moderate blue andseveral showed zoned fluorescence atthe boundary between the turquoiseand the interstitial matrix. Theboundary region appeared strong yel-low, while the turquoise itself fluo-resced a moderate blue.

The samples had a Mohs hardness

of 5–6, similar to high-quality (untreat-ed) turquoise. By comparison, mostpolymer-impregnated turquoise can beindented with a metal probe (Mohshardness of 5). Additionally, a hotpoint can char or blacken a polymer-impregnated stone and release an acridodor; if wax is present, the stone mayreact by sweating. When the Eljen-treated samples were tested with a hotpoint, the turquoise gave no reactionor only a very weak one (some sweat-ing was seen in samples with matrix).

Three of the cabochons tested hadbeen cut and polished by one of us(PAO). During preforming on thecoarse grinding wheel, the materialseemed harder than typical stabilizedturquoise. The good luster of the pol-ished stones was probably due to thegreater hardness. Although the matrixwas slightly softer than the turquoise,these specimens had less undercuttingthan typical polymer-impregnatedmaterial. A thin (0.7 mm) sample wascut and polished to test the strengthand behavior of thin edges during fash-ioning; the sample did not fracture andcould be polished to a sharp edge.

The Eljen samples we studied wereconsistent with the treater’s claimsregarding hardness, durability, ease ofcutting, and quality of polish. Althoughwe did not attempt to identify the spe-cific substance used in this treatment,IR spectroscopy did reveal the presenceof a polymer. Therefore, the GIALaboratory would identify this materi-al as “impregnated natural turquoise.”

Philip A. Owens and Sally Eaton-Magaña

PHOTO CREDITSJian Xin (Jae) Liao—1, 5, 6–8; PaulJohnson—2; Robison McMurtry—3;Shashikant Shah—4; Robert Weldon—10,12, 13; Donna Beaton—11.

Figure 13. These three cabochons (5.93–8.08 ct) were treated by the Eljenprocess and studied for this report.