Definition
A hydrous aluminosilicate mineral
containing some fluoride ions, used for
making refractories, glasses, and glazes. A
clear pale yellow or brown form is used as
a gemstone.
Definition
topaz: A variably coloured aluminiumsilicate mineral,Al
2(SiO
4)(OH,F)
2, that forms orthorhombiccrystals. It occurs chieflyin acid igneous rocks, such as granitesand pegmatites. Topaz is valuedas a gemstone because of its transparency,variety of colours (the wineyellowvariety being most highly prized), and great hardness (8 on theMohs’ scale). When heated, yellow orbrownish topaz often becomes arose-pink colour. The main sources oftopaz are Brazil, Russia, and the USA.
