Material Identity
Moonstone is a gem variety of the feldspar group, identified by GIA as orthoclase with the chemistry KAlSi3O8 and a Mohs hardness of 6.0 to 6.5. During formation, orthoclase and albite separate into alternating thin layers. Light scattering between these layers creates adularescence, the billowing glow that appears to drift beneath the polished surface as the stone turns. The effect is structural rather than applied, and it shows most fully when the cutter has oriented the stone with the layers in mind.
Visual Character
Adularescence can appear white, silver, or blue, and a saturated blue sheen visible across a wide viewing range is especially prized. GIA's quality guidance weighs body color, the color of the sheen, and its orientation: colorless to nearly transparent material, free of distracting inclusions and carrying a vivid blue glow, sits at the top of the scale. Cabochons dominate because their domed surface gathers the phenomenon; a cabochon cut too flat lets it slip away. Beads and faceted pieces have their own appeal, though the glow is worth confirming from the angles at which the piece will actually be worn.
Meaning and Cultural Context
Moonstone's traveling light has been linked for centuries to the moon itself, to cycles, intuition, and shifting perception. Within the feldspar family it is often discussed beside labradorite, sunstone, and opal, each with its own play of light and its own cultural history. Many wearers treat moonstone as a personal emblem of attentiveness and change, its glow a small companion for moments of transition.
Jewelry and Care
At 6.0 to 6.5 on the Mohs scale, moonstone scratches more readily than quartz, and feldspar's cleavage means a sharp knock can split a stone along its layers. Store pieces separately from harder gems, remove rings before heavy hand work, and clean only with mild soap, lukewarm water, and a soft cloth. Ultrasonic and steam cleaning are best avoided.
Choosing This Stone
Look for descriptions that specify the color of the sheen, the body color, and the angle over which the glow remains visible. Rainbow moonstone is a trade name frequently applied to labradorite, particularly material from Madagascar, rather than orthoclase moonstone; the name is established in the trade, but the two materials differ in body appearance and structure. A pale, milky bead is not the same thing as transparent blue-sheen moonstone, and clear listings distinguish them.