This stone, sometimes called titanite from its chemical compo­sition (a silicate and titanate of calcium), varies in color, but only the transparent stones are cut and used in jewelry. Even so, it is seldom seen in mounted forms, for its softness mitigates against its more general use.

In color, it is generally green, yellow, or brown, the greens being more common, and they somewhat resemble the green beryl and chrysoberyl. Transparent stones show very strong dispersion and dichroism, two marked characteristics of this stone. The "fire" of a well cut, good quality sphene is remarkable, and it excels the diamond in this respect. In fact, with its brilliance, adamantine luster, and high refractive indices, it may be sometimes confused with a colored diamond, but it is very much softer. The refrac­tive indices are 1.90-1.98, specific gravity 3.4 to 3.6, but the hard­ness is only 5 1/2. The faces and edges of a cut stone are soon worn, if used in jewelry, and they need frequent repolishing to restore brilliance to the specimen.

Cut stones are very beautiful, and when cut in brilliant form, they are very suitable to be used in mounted jewelry, except rings. Large stones are very rare; the crystals, generally small in size, are wedge shaped and flattened, and they are found in many igneous rocks, associated with feldspar, as well as in granite, gneiss, and mica schist. They are also sometimes found in crystalline lime­stone. The crystals belong to the monoclinic system of crystal­lography.

Other distinguishing features of this stone are good cleavage, and the brilliance which some specimens reveal, even when very small. When viewed in Rontgen rays, sphene is almost opaque. But with all its outstanding properties, it is unfortunate that rarity, small size, and comparative softness rules out this stone for general use in jewelry.

The chief sources of supply are the St. Gothard district of Switzerland, Madagascar, the Austrian Tyrol, and Mexico. Can­ada and the U.S.S.R. produce non-gem material. Sphene is an im­portant ore mineral from which titanium is extracted, and this is used in various industries, including those of steel and ceramics. The word sphene comes from the Greek sphen, meaning "a wedge," which is an allusion to the form of its crystals.