gemstone

Moonstone

Adularia or oligoclase feldspar, commonly showing adularescence

AI-generated identification · may be incorrect

Typically hardness 6–6.5 Mohs, pearly to vitreous luster, white-to-gray translucent body, and a floating blue-white sheen caused by feldspar intergrowths. It has two good cleavage directions and monoclinic or triclinic crystal structure; the pictured stone is polished and set in a ring.

Identified September 12, 2026More gemstone →

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Physical properties

Formation & geological history

Forms in silica-rich igneous rocks, especially pegmatites, through slow cooling and feldspar crystallization; it is generally associated with Mesozoic to younger granitic terrains. Major sources include Sri Lanka, India, Madagascar, Tanzania, Myanmar, and the United States.

Uses & applications

Used primarily in cabochon jewelry and ornamental carvings; it has little industrial use because it is relatively soft and cleaves readily.

Geological facts

Adularescence is an optical effect, not true fluorescence, produced by light scattering between fine layers of different feldspar compositions. The strongest stones display a sharp blue sheen across a transparent body.

Field identification & locations

Identify it by its soft, billowy internal glow, lack of banding, feldspar-like cleavage, and moderate hardness; glass imitations are often too uniform and bubble-bearing. Avoid ultrasonic cleaning and sharp impacts.