Moonstone

Moonstone is the most well known variety of orthoclase feldspar. A colorless to yellowish gray, highly translucent to semitransparent stone that reflects light in a distinctive shimmering phenomenon known as adularescence.
This lovely sheen is due to a combination of orthoclase and albite arranged in layers. Light reflected from the layers if they are not too thick is responsible for the unusual optical properties.
Moonstone is fairly soft (6-6.5 on the Mohs scale). Moonstone comes from Sri Lanka, India, Madagascar, Burma, Tanzania and the USA.