Topaz :

Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al₂SiO₄(F, OH)₂. Topaz crystallizes in the orthorhombic system, and its crystals are mostly prismatic terminated by pyramidal and other faces. It is one of the hardest naturally occurring minerals (Mohs hardness of 8) and is the hardest of any silicate mineral. This hardness combined with its usual transparency and variety of colors means that it has acquired wide use in jewellery as a cut gemstone as well as for intaglios and other gemstone carvings.^[5]
Topaz in its natural state is a golden brown to yellow – a characteristic which means it is sometimes confused with citrine, a less valuable gemstone.^[5] A variety of impurities and treatments may make topaz wine red, pale gray, reddish-orange, pale green, or pink (rare), and opaque to translucent/transparent. The pink and red varieties come from chromium replacing aluminium in its crystalline structure