Topaz belongs to the rhombic system of crystallization. Its cleavage
is basal and perfect, fracture uneven, hardness 8, scratching quartz
distinctly, specific gravity 3.4 to 3.6, lustre vitreous, refraction
double, and colors ranging from colorless or white to bluish-white,
light blue, wine-yellow, straw-yellow, golden-yellow, greenish- and
pale-red to pink.
Topaz becomes electric from rubbing or pressure, and retains
electricity for twenty-four hours. Before the blow-pipe topaz partly
loses color, but does not melt, and with borax it fuses slowly to a
white bead.
Topaz is partially attacked by sulphuric acid, and dissolves in salts
of phosphorus.
The composition of topaz is:
Silicon 15.05
Aluminium 30.02
Oxygen 36.08
Fluorine 17.05
Goutte d’eau or colorless topaz, sometimes called “slaves diamond,”
Siberian or bluish-white, Brazilian or golden to reddish-yellow, Saxony
or pale-wine yellow, Brazilian ruby or pink, Brazilian sapphire or
light blue, and aquamarine or greenish, are the various commercial
names for topaz.
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.