Moonstone is a potassium Feldspar of the Orthoclase family. It has a white shimmer called adularescence. The light diffraction is from thin alternating layers of Orthoclase and Albite. Moonstone is also known as Hecatolit, Chandrakanta, Feldspath Nacré.
 
Ancient Romans considered moonstone to be solidified moonlight. 
 
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* Sizes, shapes and colors my vary due to being a natural stone, being hand-carved and/or difference in computer monitors.