a gemological look at kyoceras new synthetic star ruby

8/17/2019 A Gemological Look at Kyoceras New Synthetic Star Ruby

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A GEMOLOGICAL LOOK AT KYOCERA S

NEW SYNTHETIC STAR R U B Y

B y John I . Ko ivu la a nd Rober t C. IZamnwr l ing

Kyocera Corporation of Kyo to, Japan, is currentlymarke t ing under the t rade na me Jnamor i a macro-scopically nat~tral-appearing emitransparent asteri-a ted synthe t ic ruby. W i th the except ion of obv iousintern al characteris t ics and a relatively strong fluo-rescence to ul traviolet radiat ion, al l of th e gemologi-cal properties sho wn b y this material are essential lythe sa me cis those encountered in natural s tar rubies.For the majo ri ty of gemologists wit hou t access to re-search-grade test ing equipment, the internal charac-teris t ics of l


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TABLE 1. The genfidogical properties of the Kyocera

Propwiles that overlap thoseof natural st r ruColor Slightly purpiish redVi ug appearance Vary convincing body color wit sli ht

r r t ~ f f e e t t m W the asterternRefractive l n W Spot readings of 1 76 1.77Potariscopff &on Uniaxial optic f i g wPteochroism Strong orangy fed and pwpltsh redColor fitter reaction Bright redSpecific grwffy 4-0 Â 0.02 using Gtetici's solution

withindicatorAbsorption spectrum Identiest to tk spectrum dh* by

natural ruby

~ e ydentifying propertiesUltraviolet fWe^eeweb

Long wawe Very strong redShort-wave Strong to ve^y strong fed witha

moderate to stMg superficial chalky

blue-whitewertone

Extremely fine white appear in^eixsoiution rutila. Numerous bluishwhite smoke-like swirb. Both roundand distorted gas bubble

rubies is a very natural looking slightly purplish

red that compliments their near-transparency.From the back because of their flat semipolished bases these synthetic star rubies look

synthetic. This is a cutting style gemologists haveome to associate with synthetic star corundum

similar to that produced by the Linde division ofUnion Carbide. Should these backs be roughed androunded, however, without magnification theywould look very natural.

GEMOLOGICAL PROPERTIESThe gemological properties determined on thesefive samples agreed for the most part with thosereported by Kyocera in their promotional literature. As indicated in table 1 with the exception offluorescence and internal characteristics, theproperties of the Inamori synthetic star rubyoverlap those of their natural counterparts. Thedistinctive features are described below.

Reaction t o Ultraviolet Radiation, When exposedto long-wave ultraviolet radiation, the Kyocerasynthetic star rubies all

fluoresceda very strong

red. The short-wave reaction appeared to beslightly weaker with a variable moderate tostrong] superficial chalky blue-white overtonethat was most obvious when the lamp was heldvery close to the stone and the room was in totaldarkness darkroom conditions). No phosphores-cence was observed in any of the tones. If rubies ofknown origin were used as indicators in fluores-cence testing, perhaps this reaction would proveuseful in providing evidence of synthesis.

Microscopy. When we ex mined the samples with

a gemological microscope, the first thing weno

ticed was the fineness of the exsolution "rutile"needles (figure 2 when compared t o the rutile

figure 3. The star causing xsohttion rut ls seees in t h i s Burmese d y ie much coazser

than those observed in the h mon synthetic.Incident fiber optic llumination magnified 30

238 Notes and New Techniques GEMS GEMOLOGY Winter 988


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needles typically responsible for asterism in natu-ral star mbies figure 3).

When fiber optic illumination was used, nu-merous smoke-like, bluish white, s w i r h g wispyveils were seen running haphazardly between hestar s rays Sgure 4 throughout ll five syntheticstones. These swirls are composed of white appearing matter that is far too fine to be resolvedwith a standard gemological microscope.

Similar-appearing swirls have been observedin very poor quality Czochralski-pulled syntheticruby and suggest that Kyocera s star mbies arecrystallized from a high-temperature melt process,such as Czochrahki p* rather than grown aseuhedral crystals in a flux or hydiothermal envi-ronment. The absence of curved striae suggeststhat the flame-fusion process was not used. The1.99-ct stone shows a crude hexagonal patternthrough its apex that appears to be surrounded byswirls [figure 5 nd may be the trace remnant of aseed.

Particularly distinctive of this synthetic is thepresence of gas bubbles both round and distorted

n hadowed transmitted light (figure 6 ) he swirlsare observed as dark-edged wavy bands, while thegas bubbles, although small, stand out in relativelyhigh relief.

We also noticed that one stone had a tiny chipwith a pronounced conchoidal fracture. While thistype of fracture can also be seen in natural rubiesand sapphires, it is rare in natural stones because,when put under excessive stress, natural gems aremore likely to separate along weak parting pknes,leaving a flat break s h i h o a cleavage surface.

Notes and New Techniques

Figure 5 A crude hex gon l pattern seenthrough the apex o the 1.99-ct stam m y bethe trace remnant of a seed Tiansmitted ndoblique fiber-opticilltiauttation; magai fied35 x

d general, the internal features in Kyocera sproduct in no way resemble the suite of charac-teristic inclusions recognized thus far in naturalstar corundums Giibelin and Koivula, 1986 . nthe basis of their inclusions, these new syntheticstar rubies te easy to distinguish from the natural.

INFRARED SPECTROSCOPYUsing a Nicolet 60SX Fourier-transform nfraredspectrometer, DL Emmanuel Fritsch tested themid-range infrared absorption characteristics ofone of the synthetic star rubies in a directionnormal to the cabochon s base) to check for thepossible presence of water within the structure.N o structural water could be detected.

This ack of water adds support to the premise

igme 6. n addition to the w vy patterns,sm ll gas bubbles, both round nd distorted,are sometimes observed. Shadowed transmittedlight; m smfied 50 x

GEMS . GEMOLOGY Winter 1988 239


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that Kyocera's new synthe tic s tar rubies are crys-tallized from a high-temperature melt using aprocess such as Czochralslzi pulling or Verneuilflame fusion.

QUALITATIVE CHEM ICAL ANALYSIS

Ms. Carol Stoclzton examined one of t he syn the ticstar rubies in GIA's Tracor Nor thern energy disper-sive X-ray fluorescence unit to determine quali-tatively what elements were present within thespecimen's structu re.

The cabochon was mounted, semi-polishedbase down, in a transpa rent Mylar-floored cup. Thesample chamber was evacuated and the stonesubjected to a tube voltage of 20 1zV and a tubecurrent of 0.10 mA for a 100-second measu rement .

In addition to alu min um, traces of chr omiu m(the color-producing chromophore) and titanium(th e asteriating agent) were present, as expected.

Very minor traces of calciu m and iron were alsodetected and may be the resul t of a slight co ntam-ination in the feed chemicals. The fact that nogallium was found is a very st rong indication ofsynthesis, since, in nature, aluminum-containingcompounds such as corundum always containtraces of gallium. Oxygen, another major compo-nent in this chemical system, is not detectablewith the Tracor unit.

X RAY DIFFRACTIONTo confirm the c orundum identification, we askedMr. Chu ck Fryer to d o an X-ray powder diffraction

analysis on the sample material. A spindle ofpowder from one of the cabochons was prepared

and mou nted in a Debye-Scherrer powder camera.The resulting pattern matched the JCPDS standardfor corundum, thus proving the identification.

CONCLUSIONTh is study of t he new Inamori synth eti c st ar rubywas based on an examination of only five polishedcabochons. According to Kyocera's April 1, 1987,press release, the company is marketin g only twogrades of synt het ic sta r ruby. These grades aredesignated A ( almost pure stones ) and B( very slight ly flawed stones ). Both grades wererepresented i n the samples studied by the authors.

Although very close, the key gemologicalproperties, as listed by Kyocera in their brochure,are not in exact agreement w it h those obtained bythe authors during testing. Th e properties listed inthe brochure may reflect average values for a greatnumber of stones.

With the exception of ultraviolet fluorescenceand inte rnal characteristics, a ll of t he othe r gem-ological proper ties of the se synthet ic sta r rubies,such as specific gravity and refractive index, over-lap with those shown by natural star rubies.Qualitative chemical analyses will also provide apositive identification, but the sophisticatedequipm ent necessary is not readily available t o thejeweler-gemologist. While ultraviolet fluorescencemay provide a useful clue that the material isprobably synthetic, the authors feel that thiscriterion alone is not sufficient to give a positive

identification. Microscopy is the key to identifyingKyocera's new synthetic star rubies.

REFERENCESGubelin E.J . Koivula J I (1986) Photoatlas of Inclusions in Koivula J.I ., Fritsch E., Fryer C. (1988) The gemmological

Gemstones. ABC Edition, Zurich, Switzerland. characteristics of Inamori synthet ic cat s-eye alexandriteKane R.E. (1 987) Inamori syntheti c cat s-eye alexandrite. chrysoberyl. loiirnal of Gemmology Vol. 21, No. 4, pp.

Gems a Gemology Vol. 23, No. 3, pp. 158-162. 232-236.

240 Notes-and New Techniques GEMS GEMOLOGY Winter 1988

a gemological look at kyoceras new synthetic star ruby

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