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Home , Cubic zirconia

Synthetic Cubic Stabilized Zirconia A New Effective Substitute

By RiCHARD T. LIDDICOAT, JR. and JOHN I. KOIVULA with photographs by Michael D. Waitzman and Michael R. Havstad

A Brief Description be noted. In addition, cubic zirconia Synthetic cubic stabilized zirconia, may contain small negative a newcomer in gemology, can now be arranged in sub-parallel rows that added to the growing list of diamond appear as tiny bubbles of very high substitutes. It is perhaps the most relief. The negative crystals may in satisfactory of the one-piece diamond turn be lined or partially lined with a substitutes to date. As the name white powder that is probably undiges- implies, cubic zirconia crystallizes in ted Zr02. On rare occasions negative the cubic (isometric) system. crystals may be somewhat larger and The chemical formula is Zr02 with more easily resolved. minor amounts of certain metallic As well as the colorless form, cubic oxides like oxide (CaO) or zirconia is available in a wide range of oxide (Y203) that act as colors from red to violet. Although structure stabilizing agents in the somewhat brittle, it is easily faceted o the rwise naturally monoclinic and should gain in popularity as a material. synthetic gem material. The of cubic zirconia varies between 2.15 and 2.18 Identification of Cubic Zirconia which is somewhat less than diamond's The major obstacle to overcome in fairly constant 2.42 reading. The the identification of cubic zirconia or slightly lower refractive index is, in any diamond substitute is the blinding general, balanced out by a of gemological knowledge that occurs of approximately 0.060 which is when someone is offered, at a low greater than diamond's dispersion of price, what appears to be a diamond. 0.044. Showing no and with a If a gemologist keeps in mind the hardness of 7-1/2 to 8-1/2 on the many ways in which diamond substi- Mohs scale, cubic zirconia is a very tutes may be detected, the chance of acceptable synthetic gem material. making a mistake is minimal. There are The much higher specific gravity of many ways to identify cubic zirconia. cubic zirconia, 5.60 to 5.95, compared The most important tests are based on to diamond's 3.52, makes this proper- refractive indices, specific gravity, ty a good test for gemological separa- and visual characteristics tion if the stone is unmounted. Under that become apparent both to the magnification, due to cubic zirconia's unaided eye and under magnification. much lower hardness, rounded facet If loose, the much higher specific junctions and polishing lines will often gravity of cubic zirconia is readily

58 GEMS & GEMOLOGY Growth striations in cubic zirconia. Stringers of negative crystal "gas bubbles." Magnification 10x. Magnification 2&.

EllitJJ»tlJd bYbblllIi.'partially lined with flux. Largef1U·bubb'.II~theseare rare in cubic '~ifir;~~f#i' 1~. zirconi•• Mif?1Hiriiftitm 4&.

~;ii titih>;i, 0-' .'ltull' 'me;t #iJ!r .CJI-~ ¥Immd.. . . apparent. 'With those familiar with views 8 round brilliant diamond from diamOnd $izes Md weigbll., mei'CIly just abovti thl' ptlll1C of girdle:. the weigbi"g;:the-stone wUl showiij'wdih't opPoSite Bide of thi!J lit0ne'still look$;: tQ,}l~;~epIlSi~~.l'J'Iblygreate r than tful1 ~f brillillnt-wbereas there 1liI· a dark '''V'' lit the c~t,e:r of the 'opposil~Sid,e of a :Jtt·a;I~:*~_S;t~t~e-i5¥~. auhi(! ii~C()riili. :GGC or .YAG. If il diilm oad; The- fa~to(S.iebted 10'i'efia~ ,stontlis JI~ onJtS palfUiCnt rom ~Yl...,t~'~ shOW'u. '" .p.,-;:tk'nta~~m. =w~.. .'a( f~tj, :mi,! light IJdirected onto. the the stone, pal1jQut~wh~ ~1ij!4; and $lOOl! thro~gh the tnb.lc,thtln the,~ looked at from the .side.Whe.n ~ i;lf;' thiC·~reaor bright tight· CQnUng through the stone will vary depending graph below illustrates. The inclu- on the refractive index of the material. sions in cubic zirconia, if present, There is a distinctly different appear- are also clues to its identification; ance and larger circle of light transmis- however, many stones must be studied sion on a cubic zirconia as compared to become familiar with the common to a diamond. Of course, GGG and appearance of these. YAG have even larger circles. The The reaction of cubic zirconia to same situation is true when one tries radiation varies somewhat to read printing through a stone. from stone to stone. Under longwave, Again, related to refractive index is the a medium yellow to orange fluores- appearance of a stone when immersed cence is usually encountered. The in methylene iodide with a refractive color is roughly the same, or a little index of 1.74. The loss of brilliancy in more yellow under short wave, and the cubic zirconia compared to stones have been noted that while diamond is marked to the eye. fluorescent to short wave are com- Also, one could get an idea as to pletely inert to long wave radiation. the identity of the unknown stone by Unfortunately, some cubic zirconia using a reflectivity meter, such as a shows no fluorescence. Another means Gemeter, or Jeweler's Eye. While of recognizing cubic zirconia that is reflectivity meters have inherent faults useful to those who have examined a and often give other than an accurate number of stones, is to place the reading, there is a large enough differ- stone table down on a piece of paper ence between the reflectivity of cubic with a light overhead. In this way, zirconia and that of diamond to make the cubic zirconia shows much more it easy to distinguish the substitute dispersion than does a diamond of from diamond. com parable size. A carefully polished substitute that There are several new tests' in the is as hard as cubic zirconia should have process of development that will be sharp facet edges, but those that are useful for identification of diamond polished rapidly do show rounded versus its substitutes. One is a heat facet edges, a feature never seen on a conduction test that should be on the diamond. The softer substitutes such market very shortly. Another is a new as and synthetic liquid developed by the GIA that will routinely show the rounding of write smoothly on a diamond's surface facet edges and are readily identified but will bead up on diamond substi- .as substitutes by them. The girdle tutes like cubic zirconia, GGG and surface looks different from that of YAG. ( the bruted girdle on a diamond. There and Yttrium Aluminum Garnet). will be no cleavages on acubic zir- conia, which is an important identi- . . fying characteristic of diamond . Naturals, another key diamond char- . '~- acteristic, have also been observed on . the girdles of cubic zirconias. These Natural on cubic Zirconia, Magnification 63. can be very confusing, as the photo-

60 GEMS & GEMOLOGY