Moonstone

Moonstone is a gemstone variety of the feldspar mineral group, typically potassium feldspar (orthoclase) or the related variety adularia. It is best known for adularescence, a soft, bluish to white glow that seems to billow across the stone when it is moved. This optical effect arises from minute lamellar intergrowths of feldspar minerals that scatter light.

Moonstone ranges from transparent to translucent and is usually milky or pearly with a blue sheen, though color zoning and adularescent hues can occur. Trade names such as “rainbow moonstone” are used commercially for stones that show a multicolored play of light, but true moonstone is the adularescence-dominated form; some rainbow stones are labradorite-based.

Geologically, moonstone forms in pegmatites and hydrothermal veins and is mined in several countries, most notably Sri Lanka, India, Madagascar, Brazil, Myanmar, Tanzania, and the United States.

In jewelry, moonstone is cut to display the adularescence, often as cabochons or smooth faceted stones. It has a Mohs hardness of about 6 to 6.5 and a refractive index around 1.518–1.524. Moonstone is associated with various folklore and is one of the traditional birthstones for June.

Care involves protecting it from sharp blows and avoiding prolonged exposure to direct heat. Cleaning is typically done with warm soapy water, and stones should be stored separately to prevent scratching.