What Is Moonstone? The Optics Behind Its Glow

Moonstone is a feldspar mineral, not a quartz. Its floating, billowy glow is called adularescence, and it happens because moonstone actually contains two different feldspar types — orthoclase and albite — grown together as microscopically thin, alternating layers. This structure forms as the mineral cools slowly underground, allowing the two feldspar types to separate out (a process called exsolution) into stacked layers thin enough to scatter light rather than reflect it directly, producing that soft, moving sheen.

The finest moonstone, prized for a blue-toned glow against a colorless body, comes primarily from Sri Lanka. It's often confused with labradorite, but the two show different optical effects: moonstone's light appears to float just beneath the surface, while labradorite flashes distinct colors (labradorescence) that shift sharply as the stone is tilted.