Moonstone is a sodium potassium aluminium silicate. Its name is derived from a visual effect, or sheen, caused by light diffraction within a microstructure consisting of a regular succession of feldspar layers. Moonstone is composed of two feldspar species, orthoclase and albite. The two species are intermingled. Then, as the newly formed mineral cools, the intergrowth of orthoclase and albite separates into stacked, alternating layers. When light falls between these thin, flat layers, it scatters in many directions producing the phenomenon called adularescence.