Feldspar

Feldspar
Feldspar
	Feldspar crystal 18 cm × 21 cm × 8.5 cm (7.1 in × 8.3 in × 3.3 in) from Jequitinhonha valley, Minas Gerais, southeastern Brazil
General
Category	Tectosilicate
Formula; (repeating unit)	KAlSi; 3O; 8 – NaAlSi; 3O; 8 – CaAl; 2Si; 2O; 8
IMA symbol	Fsp
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

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.

[1] 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.

[2] "Feldspar". Gemology Online. Retrieved 8 November 2012.

[Glossary2005-3] 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.

[DeerHowieZussman2001-4] 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.

[5] Anderson, Robert S.; Anderson, Suzanne P. (2010). Geomorphology: The Mechanics and Chemistry of Landscapes. Cambridge University Press. p. 187. ISBN 9781139788700.

[Rudnick2003-6] 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.

[7] 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.

[8] "Metamorphic Rocks." Metamorphic Rocks Information Archived 2007-07-01 at the Wayback Machine. Retrieved on July 18, 2007

[9] Blatt, Harvey and Tracy, Robert J. (1996) Petrology, Freeman, 2nd ed., pp. 206–210 ISBN 0-7167-2438-3

[10] "Weathering and Sedimentary Rocks." Geology. Archived 2007-07-03 at the Wayback Machine Retrieved on July 18, 2007.

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