![cover image](https://wikiwandv2-19431.kxcdn.com/_next/image?url=https://upload.wikimedia.org/wikipedia/commons/thumb/0/03/Feldspar_group.svg/640px-Feldspar_group.svg.png&w=640&q=50)
Feldspar
Group of rock-forming minerals / From Wikipedia, the free encyclopedia
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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]
Feldspar | |
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![]() 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[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] |
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/0/03/Feldspar_group.svg/320px-Feldspar_group.svg.png)
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]