Moonstone is a feldspar mineral that produces a “pearly” luster when light enters the stone and is reflected by mineral layers within the gem. Moonstone is most often a white or gray color with a glow that is white or silvery – like the glow of the moon (that’s how it got its name!). Moonstone also occurs in pink, orange, near-colorless and other colors. Rare moonstones produce a blue or a multicolored glow. These are called “rainbow moonstones” and they are market favorites. The accompanying photo shows two cabochons of rainbow moonstone with a bright blue glow.