Moonstone

Classic moonstone is feldspar material in which orthoclase and albite separate into fine layers. These layers scatter light to produce the floating sheen called adularescence. “Rainbow moonstone” in the trade is commonly labradorite; it can be beautiful, but its mineral identity differs from classic moonstone.

Moonstone is named for light rather than chemistry. Its white-blue sheen moving beneath the surface inspired the idea of moonlight gathered in stone. Art Nouveau designers used this quiet optical effect as an alternative to sharp brilliance; its lunar symbolism is directly rooted in appearance.

In spiritual use, meaning is a layer distinct from mineral properties but still open to cultural study. Moonstone is associated with cycles, intuition, transition and the non-linear rhythm of time. Its sheen appears as the stone moves, suggesting that meaning sometimes emerges through a change of angle rather than a fixed gaze. Ritual may use it to mark lunar phases or personal turning points.

Sources: 1, 2, 3.