TOPAZ

'Topaz' is a silicate mineral of aluminium and fluorine with the chemical formula Al₂SiO₄(F,OH)₂. It crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. It has an easy and perfect basal cleavage, meaning that gemstones or other fine specimens have to be handled with care to avoid developing cleavage flaws. The fracture is conchoidal to uneven. Topaz has a hardness of 8, a specific gravity of 3.4–3.6, and a vitreous luster. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. They may also be white, gray, green, blue, pink or reddish-yellow and transparent or translucent. When heated, yellow topaz often becomes reddish-pink. Topaz can also be irradiated, turning the stone blue, ranging from a light pure color to very dark almost electric blue. A recent trend in jewelry is the manufacture of topaz specimens that display iridescent colors, by applying a thin layer of titanium oxide via physical vapor deposition, this stone is then sold as 'mystic topaz'.
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 like those at Topaz Mountain in western Utah. It may be found with fluorite and cassiterite. It can be found in the Ural and Ilmen mountains, Afghanistan, Czech Republic, Germany, Norway, Pakistan, Italy, Sweden, Japan, Brazil, Mexico, and the United States.
Topaz crystals from Brazilian pegmatites are up to 80cm x 60cm x 60cm in size.^[1] The biggest topaz crystal ever found, named "El Dorado", was found in Brazil in 1984. It weighs 6.2 kg and belongs to the British Royal Collection.

Contents

Etymology and historical and mythical usage

References

External links

Etymology and historical and mythical usage

The name "topaz" is derived from the Greek ''tòpazi[òs]'', which was the name of an island in the Red Sea that was difficult to find and from which a yellow stone (now believed to be chrysolite: yellowish olivine) was mined in ancient times; topaz itself (rather than ''topazios'') wasn't really known about before the classical era. In the Middle Ages the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above.
Many modern English translations of the Bible, including the King James Version mention ''topaz'' in Exodus 28:17 in reference to a stone in the Hoshen: "And thou shalt set in it settings of stones, even four rows of stones: the first row shall be a sardius, a topaz, and a carbuncle: this shall be the first row." However, since these translations as ''topaz'' all derive from the Septuagint translation ''tòpazi[òs]'', which as mentioned above referred to a yellow stone that wasn't topaz, probably chrysolite, it should be borne in mind that topaz is not meant here. The masoretic text (the Hebrew on which most modern bible translations of the Old Testament are based) has ''pitdah'' as the gem the stone is made from; ''pitdah'' is of unknown meaning, though scholars think it is related to an Assyrian word meaning ''flashed''. There is a wide range of views among traditional sources about which tribe of the Israelites the stone refers to.
Yellow topaz is the traditional November birthstone, and the state gemstone for Utah.

References

★ Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy'', 20th ed., ISBN 0-471-80580-7
1. ''The Complete Encyclopedia of Minerals'' by P. Korbel and M. Novak

External links

★ Webmineral

★ Mindat with location data

★ Mineral galleries