Topaz is a mineral occurring in rhombic prisms, generally yellowish and pellucid, also colourless, and of greenesh, bluish, or brownish shades. It sometimes occurs massive and opaque. It is a fuosilicate of alumina, and is used as a gem. It is formed by flourine-bearing vapors given off during the last stages of the solidification of igneous rocks and has the formulae Al2SiO4 (F,OH)2 and a relative hardness of 8.
No related terms.