Group: Silicates – tectosilicates
Chemical composition: KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8
Colors: pink, white, gray, brown
Formation: triclinic or monoclinic
Principal Sources: Italy, Turkey, China
Special Notes: Feldspar is derived from the German Feld “field” and Spath “a rock that does not contain ore.” Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth’s crust. Feldspars crystallize from magma in both intrusive and extrusive igneous rocks, as veins, and are also present in many types of metamorphic rock. Feldspar is a common raw material used in glassmaking, ceramics, and to some extent as a filler and extender in paint, plastics, and rubber. In glassmaking, alumina from feldspar improves product hardness, durability, and resistance to chemical corrosion.