Moonstone (Orthoclase Feldspar)

Physical Properties

Hardness: 6-6.5 on Mohs scale; Color: peach, tan, white, or gray; Luster: vitreous to pearly; Crystal structure: monoclinic or triclinic; Cleavage: perfect; Specific gravity: 2.56-2.59

Formation & Geological History

Formed in plutonic igneous rocks (pegmatites) through the intergrowth of orthoclase and albite. As the magma cools, the two minerals separate into thin, alternating layers called lamellae.

Uses & Applications

Primarily used as a gemstone in jewelry (rings, pendants, earrings), and as a popular specimen for crystal healing and mineral collectors.

Geological Facts

The unique play of light seen in Moonstone is called adularescence, caused by light scattering between microscopic layers of different feldspar minerals. It is the Florida State Gemstone, designated in 1970 to honor the Moon landings.

Field Identification & Locations

Identify by its pearly luster and internal shimmers of light (adularescence). Commonly found in Sri Lanka, India, Myanmar, and Madagascar. In the field, look for characteristic feldspar cleavage planes.

Identified on: 4/30/2026

Mode: Standard