topaz

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Topaz from Minas Gerais state, Brazil (credit: Lee Boltin)

Aluminum silicate mineral, Al₂SiO₄(F,OH)₂, that is valued as a gemstone. It is formed by fluorine-bearing vapours given off during the last stages of the crystallization of igneous rocks. Pure topaz may be colourless and, when brilliant-cut, has been mistaken for diamond. It may also be various shades of yellow, blue, or brown. Imperial topaz, with vivid reddish orange colour, from Minas Gerais, Braz., is very highly valued.

For more information on topaz, visit Britannica.com.

A mineral best known for its use as a gemstone. Crystals are usually colorless but may be red, yellow, green, blue, or brown. The wine-yellow variety is the one usually cut and most highly prized as a gem. Corundum of similar color sometimes goes under the name of Oriental topaz. Citrine, a yellow variety of quartz, is the most common substitute and may be sold as quartz topaz.

Topaz is a nesosilicate with chemical composition Al₂SiO₄(F,OH)₂. The mineral crystallizes in the orthorhombic system and is commonly found in well-developed prismatic crystals with pyramidal terminations. It has a perfect basal cleavage which enables it to be distinguished from minerals otherwise similar in appearance. Hardness is 8 on Mohs scale; specific gravity is 3.4–3.6. See also Hardness scales.

Fine yellow and blue crystals have come from Siberia and much of the wine-yellow gem material from Minas Gerais, Brazil. In the United States topaz has been found near Florissant, Colorado; in Thomas Range, Utah; in San Diego County, California; and near Topsham, Maine. See also Gem; Silicate minerals.

Environment

In pegmatites, seams in granitic rock, high-temperature veins and replacement impregnations, and gas cavities in rhyolite.

Commonly crystallized, often in free-growing transparent crystals, sometimes very large. The c -face, the base, may be conspicuous or may be entirely missing; it is usually present. Also in parallel columnar growths (pycnite); in pseudomorphs after feldspar crystals; and in granular masses. When doubly terminated, "precious" (golden) crystals may appear hemimorphic, for the terminal faces at the two ends of the Brazilian precious topaz are usually unlike.

Colorless, white, pale blue, light yellow, yellow-brown, pinkish brown, pink, and ruby red. Luster glassy; hardness 8; specific gravity 3.5-3.6; fracture conchoidal; cleavage perfect basal. Transparent to translucent.

Aluminum fluohydroxysilicate (56.5% Al ₂ O ₃ , 33.3% SiO ₂ , and about 10% F and OH). The paragenetical habit differences are great enough to suggest major structural differences, perhaps related to the F and OH content.

Infusible, and insoluble in all but hydrofluoric acid. The powder turns blue (aluminum test) when moistened with cobalt nitrate and heated.

Great hardness and its good cleavage are excellent indications, along with its crystal form and typical occurrence and pegmatitic associations. Beryl fuses on thin edges; quartz decrepitates more violently and easily.

A valuable jewelry stone, especially in the pink, red, and brown hues. Not to be confused with the brown quartz commonly sold in Brazil and other lands (under the name topaz, as in "smoky topaz."

Large topaz crystals are not common in the U.S.; the biggest are probably some crudely shaped white ones found in the pegmatite at Amelia, Virginia, associated with microcline. Clear crystals, to 4-5 in. (10 cm) across and somewhat etched, from Devils Head and Pikes Peak, Colorado; smaller crystals have come from other Colorado localities. Large and deeply etched blue crystals were found at Topsham, Maine, and many 1-2 in. (2-5 cm) crystals were found in small miarolitic cavities in granite with smoky quartz, feldspar, and phenakite at Baldface Mountain, New Hampshire. Less etched, pale blue crystals are found in Mason Co., Texas. Also important in San Diego Co., California, dikes associated with beryl and tourmaline.

Rhyolite extrusions of the Thomas Range, Utah (and, less conspicuously, of Nathrop, Colorado, and New Mexico) contain many gas cavities in which there are 1-in. (3 cm) light brown crystals, which soon fade to colorless on exposure to light. Larger but sandy crystals within the rhyolite, mostly filled with quartz and opaque, are always simpler in their terminations. It is associated in Utah with black bixbyite ([Mn,F] ₂ O ₃ ) cubes, rosy beryl (not morganite), and in Colorado with spessartine garnet. In San Luis Potosí, Mexico, similar and sometimes larger topaz appears to occur alone or perhaps with cassiterite in the rhyolite seams.

Brazilian topaz is outstanding and comes in pegmatitic colorless and blue crystals, as well as in a series of quartz veins in rich brown gemmy crystals known as "precious topaz." Pink crystals of this type have also been found in nearby hematite mines and lately in Pakistan. Small natural pink Russian topazes from the valley of the Sanarka River resemble some of the brown Brazilian gemstones, with the same crystal habit. Fine blue topaz crystals (and sherry-hued fading to blue) were found years ago in pegmatites in the Ural Mountains; lately large numbers of pale brown crystals, fading to white, have been found in Pakistan.

Though like pegmatite crystals in habit, the small crystals cut for the Saxon crown jewels were straw-hued topazes from veins in and near the "Schneckenstein" (snail stone, from its shape) in the Erzgebirge near the Czechoslovakian border.

Golden Brazilian "precious" topaz turns pink on heating, and most pink jewelry topaz has been heated, though recent finds in Pakistan are naturally pink. Topaz is a very attractive and abundant species, characterized by beautiful crystals, placing it among the more popular gemstones with collectors. The common deep blue topaz now so abundant in the jewelry trade is largely irradiated white material; no naturally blue topaz ever reaches such a rich hue.

• Gemstones
• Brown

This article is about the mineral or gemstone. For other uses, see Topaz (disambiguation).

Topaz
A group of topaz crystals on matrix
General
Category	Silicate mineral
Chemical formula	Al2SiO4(F,OH)2
Strunz classification	9.AF.35
Crystal symmetry	Orthorhombic dipyramidal H-M symbol: (2/m 2/m 2/m) Space group: Pbnm
Unit cell	a = 4.65 Å, b = 8.8 Å, c = 8.4 Å; Z = 4
Identification
Color	Colorless (if no impurities), blue, brown, orange, gray, yellow, green, pink and reddish pink
Crystal habit	Prismatic crystals with faces striated parallel to long dimension; also columnar, compact, massive
Crystal system	Orthorhombic
Cleavage	[001] Perfect
Fracture	Subconchoidal to uneven
Mohs scale hardness	8 (defining mineral)
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	3.49–3.57
Optical properties	Biaxial (+)
Refractive index	nα = 1.606–1.629 nβ = 1.609–1.631 nγ = 1.616–1.638
Birefringence	δ = 0.010
Pleochroism	Weak in thick sections X = yellow; Y = yellow, violet, reddish; Z = violet, bluish, yellow, pink
Other characteristics	Fluorescent, short UV=golden yellow, long UV=cream
References	[1][2][3][4]

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.

Contents 1 Color and varieties 2 Localities and occurrence 3 Etymology and historical and mythical usage 3.1 Etymology 3.2 History 3.3 Biblical background, etymology, and analysis 4 References 5 External links

Color and varieties

Facet Cut Topaz Gemstones in various colors

Pure topaz is colorless and transparent but is usually tinted by impurities; typical topaz is wine, yellow, pale gray, reddish-orange, or blue brown. It can also be made white, pale green, blue, gold, pink (rare), reddish-yellow or opaque to transparent/translucent.

Orange topaz, also known as precious topaz, is the traditional November birthstone, the symbol of friendship, and the state gemstone for the US state of Utah.^[5]

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.^[6][7]

Blue topaz is the US state Texas' gemstone.^[8] 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.^[7]

Mystic topaz is colorless topaz which has been artificially coated giving it the desired rainbow effect.^[9]

Localities and occurrence

Topaz Mountain, Utah

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 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.

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 Aurungzebe, observed by Jean Baptiste Tavernier measured 157.75 carats.^[10] The American Golden Topaz, a more recent gem, measured a massive 22,892.5 carats.

Colorless and light-blue varieties of topaz are found in Precambrian granite in Mason County, Texas^[11] within the Llano Uplift. There is no commercial mining of topaz in that area.^[12]

Etymology and historical and mythical usage

Etymology

Colorless topaz, Minas Gerais, Brazil

The name "topaz" is derived (via Old French: Topace and Latin: Topazus) from the Greek Τοπάζιος (Τοpáziοs) or Τοπάζιον (Τοpáziοn),^[13] the ancient name of St. John's Island in the Red Sea which 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.

Pliny says that Topazos is a legendary island in the Red Sea and the mineral "topaz" was first mined there. The word topaz might be related to the Arabic word توباز which meant "the subject of the search" or Sanskrit word तपस् "tapas" meaning "heat" or "fire."^[13]

History

Nicols, the author of one of the first systematic treatises on minerals and gemstones, dedicated two chapters to the topic in 1652.^[14] In the Middle Ages, the name topaz was used to refer to any yellow gemstone, but in modern times it denotes only the silicate described above.

Biblical background, etymology, and analysis

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 (garnet): this shall be the first row."

However, because these translations as topaz all derive from the Septuagint translation topazi[os], which as mentioned above referred to a yellow stone that was not topaz, but probably chrysolite, it should be borne in mind that topaz is likely not meant here.^[15] The masoretic text (the Hebrew on which most modern Protestant Bible translations of the Old Testament are based) has pitdah as the gem the stone is made from; some scholars think it is related to an Assyrian word meaning "flashed".^{[citation needed]} More likely, pitdah is derived from Sanskrit words (पीत pit = yellow, दह् dah = burn), meaning "yellow burn" or, metaphorically, "fiery".

References

1. ^ Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7
2. ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W. and Nichols, Monte C., ed. (1995). "Topaz" (PDF). Handbook of Mineralogy. II (Silica, Silicates). Chantilly, VA, US: Mineralogical Society of America. ISBN 0-9622097-1-6. http://rruff.geo.arizona.edu/doclib/hom/topaz.pdf. Retrieved December 5, 2011. 
3. ^ Topaz. Mindat.org. Retrieved on 2011-10-29.
4. ^ Topaz. Webmineral.com. Retrieved on 2011-10-29.
5. ^ Utah State Gem – Topaz. Pioneer.utah.gov (2010-06-16). Retrieved on 2011-10-29.
6. ^ Imperial Topaz, Natural History Museum of Los Angeles County
7. ^ ^{a b} Gemstones & Gemology – Topaz, Emporia State University
8. ^ State Gem – Texas Blue Topaz. State Gemstone Cut – Lone Star Cut. state.tx.us
9. ^ Mystic Topaz, Consumer Information. Farlang.com (2008-10-30). Retrieved on 2011-10-29.
10. ^ Famous and Notheworthy Topazes Rao Bahadur, A Handbook of Precious Stones, Geological Survey of India
11. ^ Handbook of Texas Online – Mineral Resources and Mining. Tshaonline.org. Retrieved on 2011-10-29.
12. ^ Mason, Texas Chamber of Commerce Web site
13. ^ ^{a b} Harper, Douglas. "potash". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=potash. 
14. ^ A Lapidary or History of Gemstones, University of Cambridge, 1652.
15. ^ See for extensive discussion Oliver Farrington, Gems and Gem Minerals, Chicago, 1903, p. 119. Farrington was curator of Natural History Museum in Chicago.

External links

Wikimedia Commons has media related to: Topaz

• Pink Topaz, Biblical Topaz References Farlang – gem information and full text historical references
• Topaz and other minerals found at Topaz Mountain, Juab County, Utah Geological Survey

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Dansk (Danish)
n. - topas

Nederlands (Dutch)
topaas

Français (French)
n. - topaze

Deutsch (German)
n. - Topas

Ελληνική (Greek)
n. - (ορυκτολ.) τοπάζι

Italiano (Italian)
topazio

Português (Portuguese)
n. - topázio (m)

Русский (Russian)
топаз

Español (Spanish)
n. - topacio

Svenska (Swedish)
n. - topas

中文（简体）(Chinese (Simplified))
黄晶, 南美蜂鸟, 黄玉

中文（繁體）(Chinese (Traditional))
n. - 黃晶, 南美蜂鳥, 黃玉

한국어 (Korean)
n. - 황옥, 벌새의 일종

日本語 (Japanese)
n. - 黄玉, トパーズ

العربيه (Arabic)
‏(الاسم) حجر كريم مختلف ألأشكال وألألوان, ألتوباز‏

עברית (Hebrew)
n. - ‮טופז, פטדה‬

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