Topaz
Topaz crystal on white matrix
General
CategoryNesosilicate minerals
Formula
(repeating unit)		Al2SiO4(F,OH)2
IMA symbolTpz[1]
Strunz classification9.AF.35
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPbnm
Unit cella = 4.65 Å, b = 8.8 Å,
c = 8.4 Å; Z = 4
Identification
ColorColorless (if there are no impurities), white, blue, brown, orange, gray, yellow, yellowish brown, green, pink, reddish pink or even red
Crystal habitPrismatic crystal
TwinningRarely on [111][2]
Cleavage[001] Perfect
FractureSubconchoidal to uneven
Mohs scale hardness8 (defining mineral)
LusterVitreous
StreakWhite
DiaphaneityTransparent
Specific gravity3.49–3.57
Optical propertiesBiaxial (+)
Refractive indexnα = 1.606–1.629
nβ = 1.609–1.631
nγ = 1.616–1.638
Birefringenceδ = 0.010
PleochroismWeak in thick sections X = yellow; Y = yellow, violet, reddish; Z = violet, bluish, yellow, pink
Ultraviolet fluorescenceShort UV=golden yellow; Long UV=cream
References[3][4][5][6]

Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. It is used as a gemstone in jewelry and other adornments. Common topaz in its natural state is colorless, though trace element impurities can make it pale blue or golden brown to yellow orange. Topaz is often treated with heat or radiation to make it a deep blue, reddish-orange, pale green, pink, or purple.

Although it is often associated with golden yellow and blue, it comes in a variety of colors, including colorless. The rarest are natural pinks, reds, and delicate golden oranges, sometimes with pink hues.[7]

Topaz is a nesosilicate mineral. It is one of the hardest naturally occurring minerals and has a relatively low index of refraction. It occurs in many places in the world.

Etymology

The name "topaz" is usually believed to be derived (via Old French: Topace and Latin: Topazius) from the Greek Τοπάζιος (Topázios) or Τοπάζιον (Topázion),[8] from Τοπαζος. This is 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. The name topaz was first applied to the mineral now known by that name in 1737.[9] Ancient Sri Lanka (Tamraparni) exported native oriental topazes to Greece and ancient Egypt, which led to the etymologically related names of the island by Alexander Polyhistor (Topazius) and the early Egyptians (Topapwene) – "land of the Topaz".[10][11] Pliny said that Topazos is a legendary island in the Red Sea and the mineral "topaz" was first mined there. Alternatively, the word topaz may be related to the Sanskrit word तपस् "tapas", meaning "heat" or "fire".[8]

History

Nicols, the author of one of the first systematic treatises on minerals and gemstones, dedicated two chapters to the topic in 1652.[12] 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.

Many English translations of the Bible, including the King James Version, mention topaz. However, because these translations as topaz all derive from the Septuagint translation topazi[os], which referred to a yellow stone that was not topaz, but probably chrysolite (chrysoberyl or peridot), topaz is likely not meant here.[13]

An English superstition also held that topaz cured lunacy.[14] The ancient Romans believed that topaz provided protection from danger while traveling.[15] During the Middle Ages, it was believed that attaching the topaz to the left arm protected the owner from any curse and warded off the evil eye. It was also believed that wearing topaz increased body heat, which would enable people to relieve a cold or fever.[16] In Europe during the Middle Ages, topaz was believed to enhance mental powers.[17]

Gemstone

Topaz is a gemstone. In cut and polished form, it is used to make jewelry or other adornments. It also has other uses. Orange topaz, also known as precious topaz, is the conventional birthstone for November, the symbol of friendship and the state gemstone of the U.S. state of Utah.[18] Blue topaz is the state gemstone of the US state of Texas.[19]

Characteristics

Blue topaz crystal

Topaz in its natural state is colorless, often with a greyish cast. It also occurs as a golden brown to yellow which makes it sometimes confused with citrine, a less valuable gemstone.[20] The specific gravity of all shades of topaz, however, means that it is considerably heavier than citrine (about 25% per volume) and this difference in weight can be used to distinguish two stones of equal volume. Also, if the volume of a given stone can be determined, its weight if it were topaz can be established and then checked with a sensitive scale. Likewise, glass stones are also much lighter than equally sized topaz.

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.

Sherry-colored topaz from Utah, USA

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.[21][22] 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.[22] Mystic topaz is colorless topaz which has been artificially coated via a vapor deposition process giving it a rainbow effect on its surface.[23]

Although very hard, topaz must be treated with greater care than some other minerals of similar hardness (such as corundum) because of a weakness of atomic bonding of the stone's molecules along one or another axial plane (whereas diamonds, for example, are composed of carbon atoms bonded to each other with equal strength along all of its planes). This gives topaz a tendency to break along such a cleavage plane if struck with sufficient force.[24]

Topaz has a relatively low index of refraction for a gemstone, and so stones with large facets or tables do not sparkle as readily as stones cut from minerals with higher refractive indices, though quality colorless topaz sparkles and shows more "life" than similarly cut quartz. When given a typical "brilliant" cut, topaz may either show a sparkling table facet surrounded by dead-looking crown facets or a ring of sparkling crown facets with a dull well-like table.[25] It also takes an exceptionally fine polish, and can sometimes be distinguished from citrine by its slippery feel alone (quartz cannot be polished to this level of smoothness).[26]

Another method of distinguishing topaz from quartz is by placing the unset stone in a solution of bromoform or methylene iodide. Quartz will invariably float in these solutions, whereas topaz will sink.[26]

Localities and occurrence

Main topaz producing countries

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 Ilmensky mountains of Russia, in Afghanistan, Sri Lanka, the 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,[27] some clear topaz crystals from Brazilian pegmatites can reach boulder size and weigh hundreds of pounds. The Topaz of Aurangzeb, observed by Jean Baptiste Tavernier weighed 157.75 carats (31.550 g).[28] The American Golden Topaz, a more recent gem, weighed 22,892.5 carats (4,578.50 g). Large, vivid blue topaz specimens from the St. Anns mine in Zimbabwe were found in the late 1980s.[29] Colorless and light-blue varieties of topaz are found in Precambrian granite in Mason County, Texas[30] within the Llano Uplift. There is no commercial mining of topaz in that area.[31] It is possible to synthesize topaz.[32]

See also

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ↑ Nesse, William D. (2000). Introduction to mineralogy. New York: Oxford University Press. p. 313. ISBN 9780195106916.
  3. ↑ Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20 ed.). ISBN 0-471-80580-7.
  4. ↑ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (1995). "Topaz" (PDF). Handbook of Mineralogy. Vol. II (Silica, Silicates). Chantilly, VA, US: Mineralogical Society of America. ISBN 978-0-9622097-1-0. Retrieved December 5, 2011.
  5. ↑ Topaz. Mindat.org. Retrieved on 2011-10-29.
  6. ↑ Topaz. Webmineral.com. Retrieved on 2011-10-29.
  7. ↑ "Topaz Value, Price, and Jewelry Information". International Gem Society. Retrieved 2021-11-16.
  8. 1 2 Harper, Douglas. "topaz". Online Etymology Dictionary.
  9. ↑ Hurlbut & Klein 1985.
  10. ↑ Suckling, Horatio John (1876). Ceylon: A General Description of the Island, Historical, Physical, Statistical. Containing the Most Recent Information. Chapman & Hall. p. 10. Retrieved 28 June 2019. topaz taprobane.
  11. ↑ "Astrological Magazine". Astrological Magazine. 56 (1–6): 75. 1967. Retrieved 28 June 2019.
  12. ↑ A Lapidary or History of Gemstones, University of Cambridge, 1652.
  13. ↑ Farrington, Oliver (1903) Gems and Gem Minerals. Chicago. p. 119.
  14. ↑ Pettigrew, Thomas Joseph (1844) On Superstitions Connected with the History and Practice of Medicine and Surgery. Philadelphia E. Barrington and G.D. Haswell. p. 70.
  15. ↑ Webster, R. (2012). The encyclopedia of superstitions. Llewellyn Worldwide. p. 256. ISBN 9780738725611.
  16. ↑ Webster 2012, p. 260.
  17. ↑ Simmons, Robert (2005). The book of stones : who they are & what they teach. East Montpelier, VT: Heaven and Earth Pub. p. 403. ISBN 978-0962191039.
  18. ↑ "Utah State gem – Topaz". Pioneer.utah.gov. 16 June 2010. Archived from the original on 14 November 2012. Retrieved 29 October 2011.
  19. ↑ "Texas state gem – Blue Topaz. State gemstone cut – Lone Star cut". state.tx.us. Archived from the original on 2009-03-12.
  20. ↑ Hurrell, Karen; Johnson, Mary L. (15 December 2016). Gemstones: A Complete Color Reference for Precious and Semiprecious Stones of the World. Book Sales. p. 169. ISBN 978-0-7858-3498-4.
  21. ↑ "Imperial topaz". nhm.org. Natural History Museum of Los Angeles County. Archived from the original on 13 May 2009.
  22. 1 2 "Gemstones & Gemology – Topaz". academic.emporia.edu. Emporia State University.
  23. ↑ "Mystic topaz, consumer information". Farlang.com. 30 October 2008. Retrieved 29 October 2011.
  24. ↑ Newman, Renee (7 January 2015). Gem & Jewelry Pocket Guide: A traveler's guide to buying diamonds, colored gems, pearls, gold and platinum jewelry. BookBaby. p. 104. ISBN 978-0-929975-49-8.
  25. ↑ Dake, H. (16 April 2013). The Art of Gem Cutting – including cabochons, faceting, Sspheres, tumbling, and special techniques. Read Books Limited. p. 105. ISBN 978-1-4474-8480-6.
  26. 1 2 B. Anderson (2011). Gem Testing. Read Books.
  27. ↑ "Topaz Guide". Ayana Jewellery. Archived from the original on November 24, 2016. Retrieved November 23, 2016.
  28. ↑ Famous and Notheworthy Topazes Rao Bahadur, A Handbook of Precious Stones, Geological Survey of India
  29. ↑ "Topaz (Blue)". Cape Minerals. Archived from the original on 8 February 2017. Retrieved 7 February 2017.
  30. ↑ Handbook of Texas Online – Mineral Resources and Mining. Tshaonline.org. Retrieved on 2011-10-29.
  31. ↑ Mason, Texas Chamber of Commerce Web site
  32. ↑ Rosenberg, Philip E. (1972). "Compositional variations in synthetic topaz" (PDF). American Mineralogist. 57: 169–187.
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