Topaz

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Topaz
Specific gravity
3.49–3.57
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.[7] Topaz is often treated with heat or radiation to make it a deep blue, reddish-orange, pale green, pink, or purple.[8]

Topaz is a

crystal class.[10]

It occurs in many places in the world. Some of the most popular places that topaz is sourced is Brazil and Russia.[7]

Etymology

The name "topaz" is usually believed to be derived (via

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".[11]

History

Nicols, the author of one of the first systematic treatises on minerals and gemstones, dedicated two chapters to the topic in 1652.[15] 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.[16]

An English superstition also held that topaz cured lunacy.[17] The ancient Romans believed that topaz provided protection from danger while traveling.[18] 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.[19] In Europe during the Middle Ages, topaz was believed to enhance mental powers.[20] In India, people believed topaz granted beauty, intelligence and longevity when worn over the heart.[21]

Gemstone

Topaz is a gemstone. In cut and polished form, it is used to make jewelry or other adornments. Lower quality topaz is commonly used as an abrasive material due to its hardness and it is used to produce refractory materials for high temperature environments.[7] Topaz can be used as a flux in steel production[22]. Using topaz as a refectory material does have some health and environmental concerns due to the production of fluorine as a byproduct of calcining topaz.

Topaz is a part of the second rank of gemstones, or semiprecious stones, accompanying aquamarine, morganite, and tourmaline.[7] The first rank of gemstones, or precious stones, includes ruby, sapphire, diamond, and emerald.

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.[23] Blue topaz is the state gemstone of the US state of Texas.[24] The 4th wedding anniversary gem is blue topaz and the 23rd is imperial topaz.[21]

Synthetic topaz can be produced using a method that includes the thermal hydrolysis of SiO2 and AlF3.[25] When these compounds are heated to temperatures of 750° to 850 °C topaz is formed. Another method uses a combination of amorphous Al2O3, Na2SiF6, and water which is heated to a temperature of 500 °C, put under a pressure of 4000 bars and left for 9 days.[25]

On occasion, cavities can be found within topaz and they have been historically filled using a liquid called brewsterlinite.[25] This liquid is a hydrocarbon [26] with a refractive index of 1·13.[25]

To care for a topaz gemstone, it is best to avoid ultrasonic cleaners or steam as this could produce small fractures within the crystal.[21] Warm water with soap is the best way to wash it.

Mineralogy

Topaz's crystal structure using polyhedrons showcasing the aluminum octahedron (grey), silica tetrahedron (blue), oxygen (red), and fluorine (green).

Topaz is an accessory mineral to felsic igneous, sedimentary, and hydrothermally altered rocks.[27]

The crystal structure of topaz alternates between sheets of (F, OH)2O and O along (010) with Al3+ occupying the octahedral sites and Si4+ in the tetrahedral sites.[27] Fluorine can be substituted by hydroxide in topaz by up to 30 mol.% in nature and hydroxide dominating topaz can be made in lab but has not been found in nature.[28]

Topaz's crystal habit takes many forms. It can display a range of slender and long crystals to bulky and short.[28] There can also be variation in the terminations displaying blunt, pyramidal, chisel or wedge shaped terminations. The perfect cleavage {001} in topaz breaks no Si-O bonds within its structure and only breaks Al-O and Al-F bonds.[29] This cleavage is diagnostic for this mineral. The 2V optical angle in topaz can range from 48° to 69.5°.[28] Low fluorine content yields a smaller angle and high fluorine content yields a larger angle.

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 color which makes it sometimes confused with

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.[31]

Large topaz gemstone and small irradiated topaz fragment on display at the Smithsonian Museum of Natural History.

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 from exposure to sunlight for an extended period of time.

vapor deposition process giving it a rainbow effect on its surface.[34]

Sherry-colored topaz from Utah, USA

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.[35]

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.[36] 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).[37]

Another method of distinguishing topaz from quartz is by placing the unset stone in a solution of

methylene iodide. Quartz will invariably float in these solutions, whereas topaz will sink.[37]

Localities and occurrence

Main topaz producing countries

Topaz is commonly associated with

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. Topaz was found around the time of the 1700s in a pegmatite formation within the central Urals Mountains in Russia.[7]

Topaz varieties found in Pakistan.

Brazil is one of the largest producers of topaz,

Jean Baptiste Tavernier weighed 157.75 carats (31.550 g).[39] 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.[40] Colorless and light-blue varieties of topaz are found in Precambrian granite in Mason County, Texas[41] within the Llano Uplift. There is no commercial mining of topaz in that area.[42] It is possible to synthesize topaz.[43]

Mining

Large-scale topaz mining typically uses open pit and underground mining to extract the gem[44]. The waste material is discarded using large machines to transport it away while the valuable ore is washed and sorted to recover the topaz gems.

In smaller scale mines, dry sieving is used in alluvial environments by shovelling the material in sieves to separate the gems from unwanted dust and debris[44]. The topaz can then be selected out by hand from the remaining material.

Mined topaz is then sent to be processed for use in jewelry by polishing the gem and treating it to achieve the desired colour[44].

Mining for topaz can cause some environmental concerns mostly associated with the larger scale operations[45]. The introduction of a large open pit mine into an environment can lead to deforestation and modification of the land around it to make it accessible to workers. The pollution produced by mining can impact the environment around it and damage its health. This disruption to the ecosystem can be challenging to the wildlife and local populations. Water is also a large component of mining operations which draws it away from neighbouring communities and creates a lack of water.

  • Topaz Mountain, Utah, United States
    Topaz Mountain, Utah, United States
  • Red topaz from Tepetate, Municipio de Villa de Arriaga, San Luis Potosí, Mexico
    Red topaz from Tepetate, Municipio de Villa de Arriaga, San Luis Potosí, Mexico
  • Facet cut topaz gemstones in various colors
    Facet cut topaz gemstones in various colors
  • Yellow topaz in stepped kite-shaped cut
    Yellow topaz in stepped kite-shaped cut
  • Imperial Topaz of Minas Gerais
    Imperial Topaz of Minas Gerais

See also

References

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  3. .
  4. . Retrieved December 5, 2011.
  5. ^ Topaz. Mindat.org. Retrieved on 2011-10-29.
  6. ^ Topaz. Webmineral.com. Retrieved on 2011-10-29.
  7. ^
    S2CID 266145193
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  8. ^ "Topaz Value, Price, and Jewelry Information". International Gem Society. Retrieved 2021-11-16.
  9. PMID 29358663
    .
  10. .
  11. ^ a b Harper, Douglas. "topaz". Online Etymology Dictionary.
  12. ^ Hurlbut & Klein 1985.
  13. ^ 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.
  14. ^ "Astrological Magazine". Astrological Magazine. 56 (1–6): 75. 1967. Retrieved 28 June 2019.
  15. ^ A Lapidary or History of Gemstones, University of Cambridge, 1652.
  16. ^ Farrington, Oliver (1903) Gems and Gem Minerals. Chicago. p. 119.
  17. ^ 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.
  18. .
  19. ^ Webster 2012, p. 260.
  20. .
  21. ^ a b c "November Birthstone". Gemological Institute of America. Retrieved 2024-02-18.
  22. ^ "Topaz" (PDF). resourcesregulator.nsw.gov. NSW Department of Primary Industries. Retrieved March 20, 2024.
  23. ^ "Utah State gem – Topaz". Pioneer.utah.gov. 16 June 2010. Archived from the original on 14 November 2012. Retrieved 29 October 2011.
  24. ^ "Texas state gem – Blue Topaz. State gemstone cut – Lone Star cut". state.tx.us. Archived from the original on 2009-03-12.
  25. ^ .
  26. ^ "Topaz - Encyclopedia". theodora.com. Retrieved 2024-02-18.
  27. ^ .
  28. ^ .
  29. .
  30. .
  31. .
  32. ^ "Imperial topaz". nhm.org. Natural History Museum of Los Angeles County. Archived from the original on 13 May 2009.
  33. ^ a b "Gemstones & Gemology – Topaz". academic.emporia.edu. Emporia State University.
  34. ^ "Mystic topaz, consumer information". Farlang.com. 30 October 2008. Retrieved 29 October 2011.
  35. .
  36. .
  37. ^ a b B. Anderson (2011). Gem Testing. Read Books.
  38. ^ "Topaz Guide". Ayana Jewellery. Archived from the original on November 24, 2016. Retrieved November 23, 2016.
  39. ^ Famous and Notheworthy Topazes Rao Bahadur, A Handbook of Precious Stones, Geological Survey of India
  40. ^ "Topaz (Blue)". Cape Minerals. Archived from the original on 8 February 2017. Retrieved 7 February 2017.
  41. ^ Handbook of Texas Online – Mineral Resources and Mining. Tshaonline.org. Retrieved on 2011-10-29.
  42. ^ Mason, Texas Chamber of Commerce Web site
  43. ^ Rosenberg, Philip E. (1972). "Compositional variations in synthetic topaz" (PDF). American Mineralogist. 57: 169–187.
  44. ^ a b c Australia, Geoscience (2020-02-07). "Topaz". Geoscience Australia. Retrieved 2024-03-20.
  45. ^ "Topaz Mining: Balancing Resource Extraction and Sustainability". www.brilliyond.com. Retrieved 2024-03-20.

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