Rainbow Moonstone

Rainbow moonstone is, despite its name, a transparent variety of labradorite, a plagioclase feldspar prized for its blue-to-multicolor flash. Here's a fact that surprises many crystal enthusiasts: rainbow moonstone is not actually moonstone. Mineralogically, it's a transparent to translucent variety of labradorite (a plagioclase feldspar) with a white body and blue-to-multicolor flash (labradorescence). True moonstone is orthoclase (a potassium feldspar) with adularescence, a billowy, moving glow.

The 'rainbow' effect in rainbow moonstone comes from the same mechanism as in standard labradorite: light diffracting off submicroscopic layers of alternating feldspar compositions within the crystal. In labradorite, these layers create the famous play of color. In rainbow moonstone, the host crystal is transparent enough to show this effect against a white or clear background.

The trade name 'rainbow moonstone' persists because it sells better than 'white labradorite' and because the visual effect (a luminous glow from within a translucent white stone) does resemble moonstone to the casual observer. Both the FTC and gemological labs recognize the name as a trade convention while noting the mineralogical distinction.

Rainbow moonstone shows blue to multicolor flashes (labradorescence) in a white translucent body. True moonstone shows a softer, billowy adularescence (typically blue or white) without the sharp, colorful flashes.

Distinguish from true moonstone (adularescence vs. labradorescence), opalite (man-made glass, too uniform), and white labradorite (same mineral, different trade name). The sharp, colorful flashes visible when tilted distinguish rainbow moonstone from the softer glow of true moonstone.