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.
Pure topaz is colorless and
transparent but is usually tinted by
impurities; typical topaz is wine red,
yellow, pale gray, reddish-orange, or
blue brown. It can also be white, pale
green, blue, gold, pink (rare),
reddish-yellow or opaque to
Orange topaz, also known as precious
topaz, is the traditional November
birthstone, the symbol of friendship,
and the state gemstone of the US state
Imperial topaz is yellow, pink (rare, if
natural) or pink-orange. Brazilian
Imperial Topaz can often have a bright
yellow to deep golden brown hue,
sometimes even violet. Many brown or
pale topazes are treated to make them
bright yellow, gold, pink or violet
colored. Some imperial topaz stones can
fade on exposure to sunlight for an
extended period of time.
Blue topaz is the state gemstone of the
US state of Texas. Naturally occurring
blue topaz is quite rare. Typically,
colorless, gray or pale yellow and blue
material is heat treated and irradiated
to produce a more desired darker blue.
Mystic topaz is colorless topaz which
has been artificially coated giving it
the desired rainbow effect.
Topaz is commonly associated with
silicic igneous rocks of the granite and
rhyolite type. It typically crystallizes
in granitic pegmatites or in vapor
cavities in rhyolite lava flows
including those at Topaz Mountain in
western Utah and Chivinar in South
America. It can be found with fluorite
and cassiterite in various areas
including the Ural and Ilmen mountains
of Russia, in Afghanistan, Sri Lanka,
Czech Republic, Germany, Norway,
Pakistan, Italy, Sweden, Japan, Brazil,
Mexico; Flinders Island, Australia;
Nigeria and the United States.
Brazil is one of the largest producers
of topaz, some clear topaz crystals from
Brazilian pegmatites can reach boulder
size and weigh hundreds of pounds.
Crystals of this size may be seen in
museum collections. The Topaz of
Aurangzeb, observed by Jean Baptiste
Tavernier weighed 157.75 carats. The
American Golden Topaz, a more recent
gem, weighed a massive 22,892.5 carats.
Large, vivid blue topaz specimens from
the St. Anns mine in Zimbabwe were found
in the late 1980s.
Colorless and light-blue varieties of
topaz are found in Precambrian granite
in Mason County, Texas within the Llano
Uplift. There is no commercial mining of
topaz in that area.