| Smoky quartz | |
| Category: | Silicate minerals |
| Formula: | SiO2 |
| Strunz: | 04.DA.05 |
| Dana: | 75.01.03.01 |
| Symmetry: | Trigonal 32 |
| Unit Cell: | a = 4.9133 Å, c = 5.4053 Å; Z=3 |
| Colour: | Brown to grey, opaque |
| Habit: | 6-sided prism ending in 6-sided pyramid (typical), drusy, fine-grained to microcrystalline, massive |
| System: | α-quartz: trigonal trapezohedral class 3 2; β-quartz: hexagonal 622[1] |
| Twinning: | Common Dauphine law, Brazil law and Japan law |
| Cleavage: | Indistinct |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Mohs: | 7 – lower in impure varieties (defining mineral) |
| Lustre: | Vitreous – waxy to dull when massive |
| Refractive: | nω = 1.543–1.545 nε = 1.552–1.554 |
| Opticalprop: | Uniaxial (+) |
| Birefringence: | +0.009 (B-G interval) |
| Pleochroism: | weak, from red-brown to green-brown |
| Streak: | White |
| Gravity: | 2.65; variable 2.59–2.63 in impure varieties |
| Melt: | 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 |
| Diaphaneity: | Transparent to nearly opaque |
| Other: | lattice: hexagonal, Piezoelectric, may be triboluminescent, chiral (hence optically active if not racemic) |
| References: | [2] [3] [4] [5] |
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]
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 Gaelic; Scottish Gaelic: sgianan-dubha (anglicised: sgian-dubhs or skean dhu).[11] The largest known cairngorm crystal is a 23.6kg (52lb) specimen kept at Braemar Castle.
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]