Moonstone is a variety of the feldspar-group mineral orthoclase. During formation, orthoclase and albite separate into alternating layers. When light falls between these thin layers it is scattered producing the phenomenon called adularescence. Adularescence is the light that appears to billow across a gem. Other feldspar minerals can also show adularescence including labradorite and sanidine.

The moonstone is characterized by an enchanting play of light. Indeed it owes its name to that mysterious shimmer which always looks different when the stone is moved and is known in the trade as 'adularescence'. In earlier times, people believed they could recognize in it the crescent and waning phases of the moon.

Moonstones from Sri Lanka, the classical country of origin of the moonstone, shimmer in pale blue on an almost transparent background. Specimens from India feature a nebulous interplay of light and shadow on a background of beige-brown, green, orange, or brown. These discreet colors, in connection with the fine shimmer, make the moonstone an ideal gemstone for jewelry with a sensual, feminine aura. This gemstone was very popular once before, about a hundred years ago at the time of Art Nouveau. It adorns a noticeably large number of the jewelry creations of the French master goldsmith René Lalique and his contemporaries, mainly to be found in museums and collections today.