Formula: (Ca,Na)(Al,Si)4O8, where Ca/(Ca + Na) (% Anorthite) is between 50%-70%
Labradorescence: It occurs in large crystal masses in anorthosite and shows a play of colors called labradorescence. The labradorescence, or schiller effect, is the result of light refracting within lamellar intergrowths resulting from phase exsolution on cooling in the Boggild miscibility gap, An48-An58.
Varieties: Gemstone varieties of labradorite exhibiting a high degree of labradorescence are called spectrolite; moonstone and sunstone are also commonly used terms, and high-quality samples with good qualities are desired for jewelry.
