A ghostly sheen moves under the surface of this feldspar, like moonlight glowing in water.
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.
Moonstone’s unearthly glow is caused by light scattering between microscopic layers of feldspar.
The minerals in the feldspar family make up more than half of the Earth’s rocky crust.
Feldspar layers that create moonstone’s sheen are similar to the size of a wavelength of light.
There are processes used to alter the color, apparent clarity, or improve the durability of gems. Some gemstones have synthetic counterparts that have essentially the same chemical, physical, and optical properties, but are grown by man in a laboratory.
Moonstone is a birthstone for June, along with pearl and alexandrite.