Plagioclase is a group of important rock-forming minerals that are part of the feldspar family. They are primarily composed of sodium and calcium aluminum silicates and are commonly found in igneous rocks like granite and basalt. Plagioclase minerals are characterized by their distinct cleavage and can vary in color from white to gray, and even to reddish hues. These minerals play a crucial role in the Earth's crust and are significant in the study of geology. Plagioclase is often used in petrology to help identify the composition of rocks and understand geological processes. Their presence can indicate the conditions under which a rock was formed.