Back Sanidien Afrikaans سانيدين Arabic Sanidin Azerbaijani Санідзін Byelorussian Sanidina Catalan Sanidin Czech Sanidin German Sanidina Spanish Sanidiin Estonian Sanidine Basque
| Sanidine | |
|---|---|
 Sanidine from Puy de Sancy, Monts-Dore massif, Puy-de-Dôme, France. Size 5 cm × 4.5 cm (2.0 in × 1.8 in) | |
| General | |
| Category | Feldspar |
| Formula (repeating unit) | K(AlSi3O8) |
| IMA symbol | Sa[1] |
| Strunz classification | 9.FA.30 |
| Dana classification | 76.01.01.02 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/m |
| Identification | |
| Color | Colorless to white |
| Crystal habit | Tabular crystals, may be acicular |
| Twinning | Carlsbad twinning common |
| Cleavage | {001} perfect, {010} good |
| Fracture | Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 6 |
| Luster | Vitreous, pearly on cleavage |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.52 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.518–1.525 nβ = 1.523–1.530 nγ = 1.525–1.531 |
| Birefringence | δ = 0.007 |
| 2V angle | Measured: 18°–42° (low); 15°–63° (high) |
| References | [2][3][4] |
Sanidine is the high temperature form of potassium feldspar with a general formula K(AlSi3O8).[2] Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures. At yet lower temperatures, microcline, a triclinic polymorph of potassium feldspar, is stable.
Due to the high temperature and rapid quenching, sanidine can contain more sodium in its structure than the two polymorphs that equilibrated at lower temperatures. Sanidine and high albite constitute a solid solution series with intermediate compositions termed anorthoclase. Exsolution of an albite phase does occur; resulting cryptoperthite can best be observed in electron microprobe images.
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ a b "The New IMA List of Minerals – A Work in Progress – Updated: March 2014" (PDF). Archived from the original (PDF) on March 25, 2014.
- ^ http://www.mindat.org/min-3521.html Mindat.org
- ^ http://www.webmineral.com/data/Sanidine.shtml Webmineral data