Smoky quartz

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Quartz
Quartz Noir variété Morion.JPG
Quartz Morion variety (Kgs 4050) from Brazil, on display at Jardin des Plantes, Paris
General
Category Silicate mineral
Formula
(repeating unit)
SiO2
Strunz classification 04.DA.05
Dana classification 75.01.03.01
Crystal symmetry 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
Crystal system α-quartz: trigonal trapezohedral class 3 2; β-quartz: hexagonal 622[1]
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[edit]

Morion[edit]

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[edit]

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[edit]

Sunglasses, in the form of flat panes of smoky quartz, were used in China in the 12th century.[9]

Gallery[edit]

See also[edit]

References[edit]

  1. ^ a b c 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. and Nichols, Monte C. (ed.). "Quartz" (PDF). Handbook of Mineralogy. 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 on Mindat
  7. ^ http://www.mindat.org/min-6270.html Morion on Mindat
  8. ^ New Oxford American Dictionary (2nd ed., 2005), p. 1102.
  9. ^ 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.

External links[edit]