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
Category	Silicate 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	weak, from red-brown to green-brown
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	lattice: 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.^{[citation needed]}

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

• List of minerals

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.

• Holden, Edward (1925). "The Cause of Color in Smoky Quartz and Amethyst" in American Mineralogist, vol. 9, pp. 203–252

External links

• Media related to Smoky quartz at Wikimedia Commons
• Works related to EB1911:Cairngorm at Wikisource
• Mineral Galleries - smoky quartz