Feldspar Feldspar Feldspars (KAlSiO – NaAlSiO – CaAlSiO) are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight. Feldspars crystallize from magma as veins in both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase feldspar (see below) is known as anorthosite. Feldspars are also found in many types of sedimentary rocks. The name "feldspar" derives from the German "Feldspat", a compound of the words "Feld", "field", and "Spat", "a rock that does not contain ore". The change from
Primary minerals in the acidic igneous rocks and a second group of accessory minerals which were formed by deposition from the residual mother liquors. Modern soil science offers the following definition: "Primary Minerals: The thickness of the earth's crust varies from 10 km under the ocean to 30 km under the continents. Of the 88 naturally occurring elements on earth, only 8 make [up] most of the crust. The earth's crust and soils are dominated by the silicic acid in combination with Na, Al, K, Ca, Fe and O ions. ...Those elements are components of primary minerals, whereas primary minerals are components