Most of the Brazilian rubies or pink topazes are produced by heating the reddish or dark-yellow variety, either in a crucible or by enveloping the stone in German tinder and setting fire to the tinder. If heated too much, the stone is apt to become colorless, and if suddenly cooled it may crack.
Colorless or white topaz takes a very high polish, and is wonderfully clear and transparent.
The great Portuguese diamond, “The Braganza,” of about 1,680 carats, is supposed to be a white topaz.
Topaz is found in the Urals, Kamschatka, Alabaschka, Miask, Nestschinsk, Adun Tschilon, Villa Rica, Boa Vista, Capao, Lana, Minas Novas, Cairngorm Mts., Schlackenwald, Zinnwald, Schneckenstein, Ehrenfriedensdorf, Altenburg, Orenburg, Mourne Mts.—Ireland, Australia, New South Wales, Ceylon, Mexico, and the United States. False topaz, or the ordinary topaz of commerce, is yellow quartz resembling yellow topaz, but lacking its brilliancy and hardness; it is also very much lighter, being only 2.5 to 2.7 in specific gravity.
Beryl and chrysolite are often mistaken for topaz, but as they are softer and beryl is much lighter, they are easily distinguished from the topaz. The strong electric property of the topaz is also a conclusive test.
Oriental topaz, or yellow corundum, is harder and heavier than the occidental or true topaz.
Apatite.
Apatite, which is seldom used as a gem stone, sometimes resembles the beryl and emerald, but is much softer and rarely has the color and brightness combined of the former gems.
This mineral, composed principally of subsesquiphosphate of lime, is 4.5 to 5. in hardness, has the specific gravity of 2.95 to 3.25, is transparent to opaque, vitreous in lustre, infusible before the blow-pipe, and dissolves slowly in nitric acid. In colors, apatite varies from colorless to sea-green, bluish-green, violet-blue, gray, yellow, red, and brown.
Apatite is found in Saxony, the Hartz Mts., Bohemia, Norway, Bavaria, England, St. Gothard in Switzerland, and in the United States.