Rainbow moonstone glows with a floating blue and multicoloured sheen over a milky white body, and here is the twist: it is technically not moonstone at all. It is a transparent to milky form of labradorite, a different feldspar, showing the same layered light-play. The trade name stuck because the glow, called adularescence, behaves just like classic moonstone's. Tilt a good stone and blue fire drifts across it like light on water. Most rainbow moonstone comes from India and Madagascar.
As a feldspar with cleavage, it needs the same care as its namesake: a hardness of 6 to 6.5 but a real dislike of sharp knocks. It shines in pendants and earrings, and rings do best with protective bezels. It is cut as high-domed cabochons to set the glow rolling, with the odd transparent stone faceted. Avoid ultrasonic cleaners and clean it with warm, soapy water. Milky glass imitations exist, but they show a flat, static shimmer rather than a glow that moves with the light.
Technically a white labradorite: it sits right between classic moonstone and labradorite in the feldspar family.
