Moonstone is a kind of feldspar, the most abundant mineral group in the crust of the Earth. Feldspar is mainly composed of silicates of aluminum with traces of other minerals such as sodium and calcium. When feldspar forms with potassium and attains a translucent, pearly form, it is known as a moonstone. The name of the moonstone comes from the similarity it has to the moon, and moonstones have been used in jewelry, especially for women, for centuries.

Several parts of the world, as well as Sri Lanka, have deposits of moonstone. Moonstone is classified as an orthoclase, meaning that it forms around volcanic and hydrothermal deposits, and has a translucent appearance, along with a sparkling luster. Moonstone is a type of orthoclase known as adularia, after the Adula Mountains of Switzerland, where the stone is abundantly circulated. Adularia crystallizes at a low temperature, and when it takes the appearance of an opalescent stone, it is classified as a moonstone.
When found in the rough, a moonstone is not an exciting sight. A skilled stone cutter must bring out the bright appearance of the stone, which must be cut with care. Normally, moonstones are cut in the form of a cabochon, a rounded and polished cut which lacks facets. The cabochon can take any form, though teardrop, round, and oval cabochons are all common. If cut properly, the stone will glitter and flow, exhibiting a property called adularescence, after the family of rock that moonstones come from.