Smoky quartz

Smoky quartz
General
Category Oxide minerals
Formula
(repeating unit)		 SiO2
Strunz classification 04.DA.05
Dana classification 75.01.03.01
Crystal system α-quartz: trigonal trapezohedral class 3 2; β-quartz: hexagonal 622[1]
Space group Trigonal 32
Unit cell a = 4.9133 Å, c = 5.4053 Å; Z=3
Identification
Colour Brown to grey, opaque
Crystal habit 6-sided prism ending in 6-sided pyramid (typical), drusy, fine-grained to microcrystalline, massive
Twinning Common Dauphine law, Brazil law and Japan law
Cleavage {0110} Indistinct
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 7 – lower in impure varieties (defining mineral)
Lustre Vitreous – waxy to dull when massive
Streak White
Diaphaneity Transparent to nearly opaque
Specific gravity 2.65; variable 2.59–2.63 in impure varieties
Optical properties Uniaxial (+)
Refractive index nω = 1.543–1.545
nε = 1.552–1.554
Birefringence +0.009 (B-G interval)
Pleochroism None
Melting point 1670 °C (β tridymite) 1713 °C (β cristobalite)[1]
Solubility Insoluble at STP; 1 ppmmass at 400 °C and 500 lb/in2 to 2600 ppmmass at 500 °C and 1500 lb/in2[1]
Other characteristics Piezoelectric, may be triboluminescent, chiral (hence optically active if not racemic)
References [2][3][4][5]

Smoky quartz is a grey, translucent variety of quartz. It ranges in clarity from almost complete transparency to a brownish-gray crystal that is almost opaque. Some can also be black.[6] Like other quartz gems, it is a silicon dioxide crystal. The smoky colour results from free silicon, formed from the silicon dioxide by natural irradiation.

Varieties

Morion

A very dark brown to black opaque variety is known as morion. Morion is the German, Danish, Spanish and Polish synonym for smoky quartz.[7] The name is from a misreading of mormorion in Pliny the Elder.[8] It has a density of 5.4.

Cairngorm

Cairngorm is a variety of smoky quartz crystal found in the Cairngorm Mountains of Scotland. It usually has a smokey yellow-brown colour, though some specimens are a grey-brown.

It is used in Scottish jewellery and as a decoration on kilt pins and the handles of sgian dubhs (anglicised: skean dhu). The largest known cairngorm crystal is a 23.6 kg (52 pound) specimen kept at Braemar Castle.

Uses

Smoky quartz is common and was not historically important, but in recent times it has become a popular gemstone, especially for jewellery.[9]

Sunglasses, in the form of flat panes of smoky quartz, were used in China in the 12th century.[10]

See also

References

  1. 1 2 3 Deer, W. A., R. A. Howie and J. Zussman, An Introduction to the Rock Forming Minerals, Logman, 1966, pp. 340–355 ISBN 0-582-44210-9
  2. ↑ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (eds.). "Quartz". Handbook of Mineralogy (PDF). III (Halides, Hydroxides, Oxides). Chantilly, VA, US: Mineralogical Society of America. ISBN 0962209724.
  3. ↑ Quartz. Mindat.org. Retrieved on 2013-03-07.
  4. ↑ Quartz. Webmineral.com. Retrieved on 2013-03-07.
  5. ↑ Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20 ed.). ISBN 0-471-80580-7.
  6. ↑ "Smoky Quartz: Smoky Quartz mineral information and data.".
  7. ↑ http://www.mindat.org/min-6270.html Morion on Mindat
  8. ↑ New Oxford American Dictionary (2nd ed., 2005), p. 1102.
  9. ↑ "The Gemstone Smoky Quartz". minerals.net. Retrieved 14 December 2015.
  10. ↑ Joseph Needham, Science & Civilisation in China (Cambridge, England: Cambridge University Press, 1962), volume IV, part 1, page 121. Needham states that dark glasses were worn by Chinese judges to hide their facial expressions during court proceedings.


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