Feldspar, which is classified as a tectosilicate mineral group, is a major constituent in the Earth's crust, comprising around 60 percent of its make-up. It is formed in igneous rocks by the crystallization of magma, and is also found in both metamorphic and sedimentary rocks. There are almost 20 different types of feldspar, with these being divided into two main groups — the plagioclase feldspars and the K-feldspars or alkali feldspars. The plagioclase feldspars include Albite, (Sodium Aluminum Silicate), Oligoclase, (Sodium Calcium Aluminum Silicate), and Labradorite (Calcium Sodium Aluminum Silicate). The K-feldspars include Microcline (Potassium Aluminum Silicate), Sanidine (Potassium Sodium Aluminum Silicate), and Orthoclase (Potassium Aluminum Silicate).