is a silicate mineral
with the chemical formula Al2SiO4
. 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.