Feldspar, any of a group of aluminosilicate minerals that contain calcium, sodium, or potassium. Feldspard make up more than half of Earth crust, and professional literature about them constitutes a large percentage of the literature of mineralogy.

Of the more than 3,000 known mineral species, less than 0.1 percent make up the bulk of Earth crust and mantle. These and an additional score of minerals serve as the basis for naming most of the rocks exposed on Earth surface.

Description and Identifying Characteristics Feldsparis derived from the German word feld,which means field, and spar, which means crystal. This name reflects the minerals abundance, as most crystalline material found in the field is feldspar. Potassium feldspard are the feldspar minerals in which the silicate tetrahedral and aluminum tetrahedra are bound with potassium ions, rather than sodium or calcium ions as in the plagioclase feldspar subgroup. The potassium feldspar group is composed of three mineral polymorphs, each having the same chemical composition, but slightly different crystal structures.

Technically these are distinct minerals, but their physical properties are so similar that they are usually only identified as potassium feldspar in the field. Using other minerals in the rock to determine the host rocks identity is often the most useful guide to their probable identity. felsic plutonic igneous rocks and metamorphic rocks Microcline