All gemstones are weighted down by the legends and lore different cultures have heaped upon them. The ancient Greeks—or the sober-minded ones, anyway—believed an amethyst worn around the neck could counteract the inebriating effects of alcohol. For warriors in Myanmar, rubies conferred invincibility. And Aztec and Mayan peoples applied the jadeite form of jade directly to their bodies to mend injuries and cure internal maladies.
Moonstones, though, are in a class by themselves when it comes to superstitious suppositions. This opalescent form of mostly orthoclase feldspar has been associated with good luck for amorous couples, a guard against epilepsy, a catalyst for bountiful crops when hung in fruit orchards, and even a predictor of the future—to summon this useful ability, one need only hold a piece of moonstone in one’s mouth during a full moon, although the duration required for the clairvoyance to manifest itself is generally not specified.
Unlike gemstones such as sapphires, moonstones are usually not artificially enhanced to goose their color and value. Moonstones come by their characteristics honestly. What you look for in a good moonstone is something called schiller, which is basically its lustre when polished. Schiller is the result of light bouncing off the stone’s thin layers of albite (producing blue hues) and thicker layers of orthoclase feldspar (the white, pearly, moon-like glow).
To bring out the schiller in a piece of moonstone, the mineral is usually formed into a rounded cabochon, worn in a ring or pendant, in which the layers of the stone run parallel to the cabochon’s flat base. That said, moonstones with inclusions, or imperfections, inside the stone are also prized since they can produce dazzling cat’s-eye effects.
Less frequently, moonstones are carved into cameos (their hardness of about a 6 on the Mohs scale makes this possible; by comparison, diamonds are at the top of the scale at 10). Because moonstones are hard enough to facet, they sometimes are cut into cushion shapes, but the stone is brittle, so cut moonstones are the exception rather than the rule.