Moonstone is the popular name used for gem-quality feldspar that exhibits the phenomenon of adularescence. Adularescence is a soft glow of light that appears to float just below the surface of a polished gemstone, usually a cabochon. The name “moonstone” was given because the floating light resembles the glow of the moon through a thin cloud cover.

The glow of moonstone is dynamic and appears to move within the stone when one of three things occurs: 1) the source of illumination moves, 2) the angle of observation is changed, or, 3) the gemstone is moved under the light. This beautiful and intriguing adularescence is what makes moonstone the most popular gemstone of the feldspar group.