Gems : Moonstone

Moonstone is the best-known gem variety of orthoclase feldspar. It is usually polished as a cabochon, or bead, and has even been carved with a moon face. It’s an important gemstone because of its sheen, known as schiller, and given the name adularescence in moonstone. The most desirable colour is blue, but moonstone also occurs in grey, white, pink, green and brown.
Moonstones can contain a number of typical flaws, or ‘inclusions’. These can look like centipede-type insects, Chinese calligraphy, negative cavities like rectangular crystals, and needle-like shapes. In large numbers, the needle-shaped inclusions can cause a cat's eye, or chatoyancy, effect.