| Feldspar | |
|---|---|
 Feldspar minerals. Clockwise from top left: Orthoclase, Albite, Microcline, and an indeterminate plagioclase | |
| General | |
| Category | Tectosilicate |
| Formula (repeating unit) | KAlSi 3O 8 – NaAlSi 3O 8 – CaAl 2Si 2O 8 |
| IMA symbol | Fsp[1] |
| Crystal system | Triclinic or monoclinic |
| Identification | |
| Color | pink, white, gray, brown, blue |
| Cleavage | two or three |
| Fracture | along cleavage planes |
| Mohs scale hardness | 6.0–6.5 |
| Luster | Vitreous |
| Streak | white |
| Diaphaneity | opaque |
| Specific gravity | 2.55–2.76 |
| Density | 2.56 |
| Refractive index | 1.518–1.526 |
| Birefringence | first order |
| Pleochroism | none |
| Other characteristics | exsolution lamellae common |
| References | [2] |
Feldspar (/ˈfɛl(d)ˌspɑːr/ FEL(D)-spar; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium.[3] The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars.[4] Feldspars make up about 60% of the Earth's crust[3] and 41% of the Earth's continental crust by weight.[5][6]
Feldspars crystallize from magma as both intrusive and extrusive igneous rocks[7] and are also present in many types of metamorphic rock.[8] Rock formed almost entirely of calcic plagioclase feldspar is known as anorthosite.[9] Feldspars are also found in many types of sedimentary rocks.[10]
- ^ 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.
- ^ "Feldspar". Gemology Online. Retrieved 8 November 2012.
- ^ a b Neuendorf, K.K.E.; Mehl, J.P. Jr.; Jackson, J.A., eds. (2005). Glossary of Geology (5th ed.). Alexandria, Virginia: American Geological Institute. p. 232. ISBN 978-0922152896.
- ^ Deer, W.A; Howie, R.A.; Zussman, J. (2001). Rock-forming Minerals (2nd edition) Volume 4A. London: Geological Society of London. p. 2. ISBN 1-86239-081-9.
- ^ Anderson, Robert S.; Anderson, Suzanne P. (2010). Geomorphology: The Mechanics and Chemistry of Landscapes. Cambridge University Press. p. 187. ISBN 9781139788700.
- ^ Rudnick, R. L.; Gao, S. (2003). "Composition of the Continental Crust". In Holland, H. D.; Turekian, K. K. (eds.). Treatise on Geochemistry. Vol. 3. New York: Elsevier Science. pp. 1–64. Bibcode:2003TrGeo...3....1R. doi:10.1016/B0-08-043751-6/03016-4. ISBN 978-0-08-043751-4.
- ^ TROLL, V. R. (2002-02-01). "Magma Mixing and Crustal Recycling Recorded in Ternary Feldspar from Compositionally Zoned Peralkaline Ignimbrite A', Gran Canaria, Canary Islands". Journal of Petrology. 43 (2): 243–270. Bibcode:2002JPet...43..243T. doi:10.1093/petrology/43.2.243. ISSN 1460-2415.
- ^ "Metamorphic Rocks." Metamorphic Rocks Information Archived 2007-07-01 at the Wayback Machine. Retrieved on July 18, 2007
- ^ Blatt, Harvey and Tracy, Robert J. (1996) Petrology, Freeman, 2nd ed., pp. 206–210 ISBN 0-7167-2438-3
- ^ "Weathering and Sedimentary Rocks." Geology. Archived 2007-07-03 at the Wayback Machine Retrieved on July 18, 2007.