Anorthite is a mineral that belongs to the plagioclase feldspar group, primarily composed of calcium and aluminum silicate. It is characterized by its white to gray color and often forms in igneous rocks, such as basalt and gabbro. Anorthite is significant in geology as it helps in understanding the formation of the Earth's crust. This mineral is also found in lunar rocks, making it important for studies related to the Moon and its geological history. Anorthite's high calcium content distinguishes it from other feldspars, which can contain varying amounts of sodium and potassium.