According to Hindu mythology, moonstone is made of solidified moonbeams. Many other cultures also associate this gem with moonlight, and it’s easy to see why. Its internal structure scatters the light that strikes it, creating a phenomenon known as adularescence. The visual effect is reminiscent of the full moon shining through a veil of thin, high clouds.
Legends say that moonstone brings good luck. 
Adularescent moonstone was once called “adularia.” The name originated with a city in Switzerland, Mt. Adular (now St. Gotthard), that was one of the first sources of fine-quality moonstone.

Great designers of the romantic Art Nouveau era, such as René Lalique and Louis Comfort Tiffany, featured the pale gem in custom jewelry. Moonstone was also a favorite among artisans of the Arts and Crafts era in the last half of the nineteenth century.
MINERAL: Feldspar
COLOR: Colorless to White, Gray, Green, Peach, Brown
REFRACTIVE INDEX: 1.518 to 1.526
BIREFRINGENCE: 0.05 to 0.008
MOHS HARDNESS: 6.0 to 6.5

-Source GIA