Smoky quartz

Smoky quartz is a brownish grey, translucent variety of quartz that ranges in clarity from almost complete transparency to an almost-opaque brownish-gray or black crystals.[6] The color of smoky quartz is produced when natural radiation, emitted from the surrounding rock, activates color centers around aluminum impurities within the crystalline quartz. [7]

Smoky quartz
General
CategorySilicate minerals
Formula
(repeating unit)		SiO2
Strunz classification04.DA.05
Dana classification75.01.03.01
Crystal systemα-quartz: trigonal trapezohedral class 3 2; β-quartz: hexagonal 622[1]
Space groupTrigonal 32
Unit cella = 4.9133 Å, c = 5.4053 Å; Z=3
Identification
ColourBrown to grey, opaque
Crystal habit6-sided prism ending in 6-sided pyramid (typical), drusy, fine-grained to microcrystalline, massive
TwinningCommon Dauphine law, Brazil law and Japan law
Cleavage{0110} Indistinct
FractureConchoidal
TenacityBrittle
Mohs scale hardness7 – lower in impure varieties (defining mineral)
LustreVitreous – waxy to dull when massive
StreakWhite
DiaphaneityTransparent to nearly opaque
Specific gravity2.65; variable 2.59–2.63 in impure varieties
Optical propertiesUniaxial (+)
Refractive indexnω = 1.543–1.545
nε = 1.552–1.554
Birefringence+0.009 (B-G interval)
Pleochroismweak, from red-brown to green-brown
Melting point1670 °C (β tridymite) 1713 °C (β cristobalite)[1]
SolubilityInsoluble at STP; 1 ppmmass at 400 °C and 500 lb/in2 to 2600 ppmmass at 500 °C and 1500 lb/in2[1]
Other characteristicslattice: hexagonal, Piezoelectric, may be triboluminescent, chiral (hence optically active if not racemic)
References[2][3][4][5]


Varieties

Morion is a very dark brown to black opaque variety. Morion is the German, Danish, Spanish and Polish synonym for smoky quartz.[8] The name is from a misreading of mormorion in Pliny the Elder.[9]

Cairngorm is a variety of smoky quartz found in the Cairngorm Mountains of Scotland.[10] It usually has a smoky yellow-brown colour, though some specimens are greyish-brown. It is used in Scottish jewellery and as a decoration on kilt pins and the handles of sgianan-dubha (anglicised: sgian-dubhs or skean dhu).[11] The largest known cairngorm crystal is a 23.6 kg (52 lb) 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 jewelry.[12]

Sunglasses, in the form of flat panes of smoky quartz, were used in China in the 12th century.[13]

See also

References
  1. 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). Vol. 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. "Smoky Quartz: A transparent brown gem & gem material".
  8. http://www.mindat.org/min-6270.html Morion on Mindat
  9. New Oxford American Dictionary (2nd ed., 2005), p. 1102.
  10. Shaw, Philip; Thompson, Des B. A. (12 June 2006). The Nature of the Cairngorms: Diversity in a Changing Environment. The Stationery Office. p. 22. ISBN 978-0-11-497326-1.
  11. Chisholm, Hugh, ed. (1911). "Cairngorm" . Encyclopædia Britannica. Vol. 4 (11th ed.). Cambridge University Press. p. 952.
  12. "The Gemstone Smoky Quartz". minerals.net. Retrieved 14 December 2015.
  13. 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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