Moonstone
Moonstone is a feldspar gemstone whose soft, billowy sheen, called adularescence, comes from light scattering within intergrown feldspar layers.
Adularescence: A floating, billowy light effect produced by light scattering within a gemstone. This optical effect is the defining sheen of moonstone.
Silicate minerals: Minerals built from silicon–oxygen tetrahedra, the dominant structural units in Earth's crust. Feldspars, including moonstone, belong to this broad mineral family.
Gemstone: A mineral, rock, or organic material cut or polished for use in adornment or collecting. Moonstone is valued and worked as a gemstone.
Pegmatite: An exceptionally coarse-grained igneous rock, commonly formed from late-stage granitic magma. Some gem-quality moonstone crystallizes in granitic pegmatites.
Rainbow moonstone: A trade name for a labradorite gemstone that shows vivid blue or multicolored flashes. Despite its name, it is generally labradorite rather than classic orthoclase moonstone.
Feldspar: A group of rock-forming aluminosilicate minerals that includes potassium, sodium, and calcium varieties. Moonstone is a feldspar variety, commonly involving orthoclase and albite.
Aluminosilicate: A silicate compound in which aluminum occupies some of the silicon positions in the structure. Feldspar chemistry is based on an aluminosilicate framework.
Cabochon: A gemstone cut with a smooth, rounded surface rather than facets. The domed surface displays moonstone's moving sheen clearly.
Sri Lanka: An island country in the Indian Ocean with important deposits of gem minerals. Sri Lanka is a major source of fine, often bluish moonstone.
Opalite: A commercial name commonly used for man-made opalescent glass sold as an imitation gemstone. Its milky glow can resemble moonstone, but it is glass rather than feldspar.