Moonstone is a variety of feldspar that displays a shimmering light effect or sheen that resembles moonlight. The effect is called adularescence or schiller and is caused by the interference of light through lamellar layers within the stone. Moonstone occurs in various colours as described below, those with a bluish colour are the most sought after and are therefore more expensive.
Moonstones can display chatoyancy, a 'cat's eye effect' made possible when sufficient amounts of parallel needle-like inclusions are present throughout the stone.
Source locations for Moonstone include: Australia, Brazil, India, Madagascar, Myanmar, Sri Lanka and the USA.
Moonstone is not normally treated.