Feldspar is the name of a large group of rock-forming silicate minerals that make up over 50% of Earth’s crust. They are found in igneous, metamorphic, and sedimentary rocks in all parts of the world. Feldspar minerals have very similar structures, chemical compositions, and physical properties. Common feldspars include orthoclase (KAlSi₃O₈), albite (NaAlSi₃O₈), and anorthite (CaAl₂Si₂O₈). Feldspars are also important constituents of gabbro and basalt, which are the primary types of rock in Earth’s oceanic crust