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.
Adularescence
Moonstone’s unearthly glow is caused by light scattering between microscopic layers of feldspar.
60%
The minerals in the feldspar family make up more than half of the Earth’s rocky crust.
0.5 Microns
Feldspar layers that create moonstone’s sheen are similar to the size of a wavelength of light.
Facts
- Mineral: Feldspar
- Chemistry: KAlSi3O8
- Color: Colorless to White, Gray, Green, Peach, Brown
- Refractive index: 1.518 to 1.526
- Birefringence: 0.05 to 0.008
- Specific gravity: 2.58
- Mohs Hardness: 6.0 to 6.5