June’s third birthstone, moonstone, was named by the Roman natural historian Pliny, who wrote that moonstone’s shimmery appearance shifted with the phases of the moon.
The most common moonstone comes from the mineral adularia, named for an early mining site near Mt. Adular in Switzerland that supplied this gemstone. This site also birthed the term adularescence, which refers to the stone’s milky glow, like moonlight floating on water.
Moonstone is composed of microscopic layers of feldspar that scatter light to cause this billowy effect of adularescence. Thinner layers produce a bluish sheen and thicker layers look white. Moonstone gems come in a range of colors spanning yellow, gray, green, blue, peach and pink, sometimes displaying a star or cat’s eye.
The finest classical moonstones, colorlessly transparent with a blue shimmer, come from Sri Lanka. Since these sources of high-quality blue moonstones have essentially been mined out, prices have risen sharply.
Moonstones are also found in India, Australia, Myanmar, Madagascar and the United States. Indian gemstones which are brown, green or orange in color are more abundant and affordably priced than their classical blue counterparts.
This beautiful gemstone’s weakness is its relatively low hardness of 6 on the Mohs scale, making it prone to stress cracking and cleaving. Care is required with moonstone jewelry like rings or bracelets; so sometimes brooches and pendants are preferred for long term durability.