Plagioclase feldspars show a complete compositional variation between sodium-rich plagioclase, albite, and calcium-rich plagioclase, anorthite. Typically white to light grey the crystal shapes are generally tabular or prismatic.

The feldspar crystal structure is complex but consists of rings of four tetrahedra strung into chains and held together ionically by metallic cations. The specific cations determine the particular variety of feldspar obtained.

Plagioclase is an important rock-forming mineral and occurs widely, primarily in igneous rocks such as basalts. It can sometimes be confused with alkali feldspars (such as orthoclase) but can be distinguished by striations on the cleavage surfaces caused by the intersection of lamellar twins with the cleavage surface.