Chemically the feldspars are silicates of aluminum, containing sodium, potassium, iron, calcium, or barium or combinations of these elements. Feldspar is found in association with all rock types, including granite, gneiss, basalt, and other crystalline rocks, and are essential constituents of most igneous rocks.
Feldspars weather to yield a large part of the clay found in soils.
Pure feldspar is colorless and transparent but the mineral is commonly opaque and found in a variety of colors. Orthoclase and microcline are called potassium or potash feldspars. They usually range from flesh color to brick red, although other colors are found, and are used in the making of porcelain and as a source of aluminum in making glass. A green variety of microcline known as amazonite, or Amazon stone, is used for ornamental purposes. The plagioclase feldspars are most commonly gray and occasionally red.