Strontium Titanate

Strontium titanate, which is manufactured by the National Lead Co. by the Verneuil process, must be added to the list of manmade gem materials. It is of particular interest because the singly refractive boules are almost colorless and the R.I. (2.409) is approximately that of diamond (2.417). Moreover, its dispersion is 0.109, compared to diamond's 0.044. This combination of high index, high dispersion, single refraction and lack of body color makes it an exceedingly attractive stone, particularly when fashioned in the emerald-cut style. Although the 2.409 R.I. is significantly lower than the same value for synthetic rutile, strontium titanate is considerably more brilliant, because less brilliancy is lost to dispersion and none to birefringence, which is the cause of the fuzziness and the reduction in the intensity of light reflections in rutile. Unfortunately, however, it is so soft (5 to 6) that it will not retain its beauty for any length of time, if it is subjected to the abuse that a ring usually takes.

Other properties are as follows:

S.G 5.13
Melting point 2090°C
Fracture conchoidal
Luster vitreous
Cleavage virtually none
Hardness 5-6
R.I 2.409

Strontium titanate is also of interest because it is a manmade gem material that has no natural counterpart. The approximate chemical composition is SrTiO3. The closest mineral in nature is perovskite, a calcium-titanium oxide (CaTiO3); in other words, calcium, which is another of the alkali-earth elements (others are barium and strontium), takes the place of the strontium of the new synthetic material. Perovskite, like strontium titanate, crystallizes in the Isometric, or cubic system.

When strontium titanate was first introduced, it was decided that a novel method of promotion would be used. The manufacturer worked with a merchandising consultant who, after investigation, concluded that no manmade material had ever been welcomed enthusiastically by jewelers. As a result, it was decided that the stone, then called "starilian," would be mounted in platinum jewelry and handled only through fashion outlets, rather than by jewelers. This merchandising method was unsuccessful; therefore, it was soon abandoned. At the preset time, it is sold by retail jewelers, who are able t0 obtain supplies from the various colored-stone houses. However, the vogue for strontium titanate, which is now marketed under the names "Bal de Feu", "Diagem", "Diamontina", "Fabulite", "Kenneth Lane Jewel", "Lustigem", "Marvelite", "Sorella", "Jewelite", "Pauline Trigers", "Wellington", have not developed to the extent that the manufacturers and colored-stone sources had hoped. Whether this is because of a lack of publicity or a reluctance on the part of jewelers to handle the material because of its comparatively low hardness and toughness is not clear. Strontium titanate is a beautiful stone, and for use in jewelry other than rings it would seem to have a significant potential.

Strontium titanate is not a particularly difficult gem material to identify. One reason for this is that its S.G. is higher than any natural transparent gem that is available in commercial quantity. However, particularly in fancy shapes, there is a possibility of visual confusion with diamond; its clarity and sharp brilliancy are more reminiscent of that stone than any other. The strength of dispersion, the present of gas bubbles as seen in Figure 1 (not always present), the nature of the girdle surface, shown in Figure 2., and the quality of polish are sufficient to identify the grained but unpolished surface that is typical and most diamond, nor does it have diamond's characteristic sharp facet edges. Also, the polishing marks that are present on most stones are usually much deeper than those on even a poorly polished diamond. Furthermore, naturals and cleavages, two features associated with diamond, never appear on strontium titanate.

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