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.
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.
| 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 |
| 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) |
| Solubility | Insoluble at STP; 1 ppmmass at 400 °C and 500 lb/in2 to 2600 ppmmass at 500 °C and 1500 lb/in2 |
| Other characteristics | lattice: hexagonal, Piezoelectric, may be triboluminescent, chiral (hence optically active if not racemic) |
| References | |
Varieties
Morion is a very dark brown to black opaque variety. Morion is the German, Danish, Spanish and Polish synonym for smoky quartz. The name is from a misreading of mormorion in Pliny the Elder.
Cairngorm is a variety of smoky quartz found in the Cairngorm Mountains of Scotland. 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). 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.
Sunglasses, in the form of flat panes of smoky quartz, were used in China in the 12th century.
See also
References
External links
Media related to Smoky quartz at Wiki Commons
Works related to EB1911:Cairngorm at Wikisource- Mineral Galleries - smoky quartz
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