Feldspars are a group of rock-forming aluminium tectosilicate minerals, containing sodium, calcium, potassium, or barium. The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust, and 41% of the Earth's continental crust by weight.
8 – NaAlSi
8 – CaAl
|Crystal system||Triclinic or monoclinic|
|Color||pink, white, gray, brown, blue|
|Cleavage||two or three|
|Fracture||along cleavage planes|
|Mohs scale hardness||6.0–6.5|
|Other characteristics||exsolution lamellae common|
Feldspars crystallize from magma as both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase feldspar is known as anorthosite. Feldspars are also found in many types of sedimentary rocks.