Moonstone
Image: <a href="//commons.wikimedia.org/wiki/User:Archaeodontosaurus" title="User:Archaeodontosaurus">Didier Descouens</a> (CC BY-SA 4.0)
Mineral NameMoonstone
Chemical Formula(Na,K)AlSi3O8
Mohs Hardness6
Crystal Systemmonoclinic
Streak Colorwhite
Cleavageperfect in two directions at nearly 90 degrees
Fractureuneven to conchoidal
Specific Gravity2.56
Colorswhite, blue, gray, peach, pink, green
Transparencytranslucent
Type LocalityMinas Gerais, Brasil
Mineral GroupSilicates (Feldspar Group)
Usesjewelry, collector
Associated Mineralsquartz, mica, other feldspars
Rarityuncommon
Description
A polished, rounded cabochon of translucent, bluish-white moonstone, displaying a prominent adularescent sheen (a billowy, shimmering light effect) across its surface.
Geological Context
Moonstone is a variety of feldspar, typically orthoclase or an intergrowth of orthoclase and albite, that forms in igneous rocks like pegmatites and syenites, as well as in some metamorphic rocks. Its characteristic adularescence is caused by light scattering from microscopic lamellar intergrowths of different feldspar layers.
