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
Yttrium point of nitrogen. Yttrium is found in most rare-earth minerals, it is found in some uranium ores, but is never found in the Earth's crust as a free element. About 31 ppm of the Earth's crust is yttrium, making it the 28th most abundant element, 400 times more common than silver. Yttrium is found in soil in concentrations between 10 and 150 ppm (dry weight average of 23 ppm) and in sea water at 9 ppt. Lunar rock samples collected during the American Apollo Project have a relatively high content of yttrium. Yttrium has no known biological role, though it