Smoky quartz
Smoky quartz | |
---|---|
Smoky quartz | |
General | |
Category | oxide mineral |
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]
Gallery
- Smoky quartz found in a stream
- Morion variety
See also
References
- 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
- ↑ 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.
- ↑ Quartz. Mindat.org. Retrieved on 2013-03-07.
- ↑ Quartz. Webmineral.com. Retrieved on 2013-03-07.
- ↑ Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20 ed.). ISBN 0-471-80580-7.
- ↑ "Smoky Quartz: Smoky Quartz mineral information and data.".
- ↑ http://www.mindat.org/min-6270.html Morion on Mindat
- ↑ New Oxford American Dictionary (2nd ed., 2005), p. 1102.
- ↑ "The Gemstone Smoky Quartz". minerals.net. Retrieved 14 December 2015.
- ↑ 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.
Wikisource has original text related to this article: |
- Holden, Edward (1925). "The Cause of Color in Smoky Quartz and Amethyst" in American Mineralologist, vol. 9, pp. 203–252
External links
Wikimedia Commons has media related to Smoky quartz. |