TOPAZ, a mineral having the composition of an aluminum fluo-silicate. It is not the topaz of Pliny and other early writers which was chrysolite (q.v.), the names having been interchanged. It generally crystallizes in or thorhombic prisms, colorless, white, yellow, or occasionally pale green or blue. Trans parent topaz, in any of its tints, is a beautiful gem. The colorless variety much resembles dia mond, and is sometimes sold for it, though its lower hardness (8) affords an easy test. What has been called the largest diamond in the world, among the Crown jewels of Portugal, is probably a colorless or "white° topaz. The yel low variety is most familiar, and is called "Bra zilian topaz,° in distinction from "Oriental to paz° (yellow sapphire) and “false,° °Scotch° or "Spanish topaz° (yellow quartz). The "Ori ental topaz° is much rarer, harder (9) and denser (about 4) ; while the "Spanish is cheaper, less hard (7) and lighter (2.65),
the density of topaz being 3.4 to 3.6. It is also distinguished by its eminent basal cleavage. The favorite shade is wine-yellow or sherry color. Both yellow and blue topaz fade and be come white by weathering or exposure to light, and some yellow varieties can be changed to a pale pink by heating, yielding the so-called "burnt topaz° or "Brazilian ruby,° resembling the pale, or Balas, variety of ruby spinel (q.v.).
Topaz occurs usually in metamorphic rocks, like gneiss, but also somewhat in igneous rocks; it is frequently, though not always, as sociated with tin-ore. The principal localities are in Ceylon, Siberia, Japan, Brazil and Mexico. In the United States it occurs in large masses at Stoneham, Me., and Trumbull, Conn.; in crystals in Colorado and Utah. Fine topaz crystals, colorless and pale blue, have re cently been found in San Diego County, Cal.