Moonstone is a variety of the feldspar-group mineral orthoclase. Moonstone is composed of microscopic layers of feldspar that scatter light to cause this billowy effect of adularescence. Moonstone comes in a range of colors spanning yellow, gray, green, blue, peach, pink and sometimes displaying a star or cat’s eye. 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. This beautiful gemstone’s weakness is its relatively low hardness of 6 on the Mohs scale, making it prone to stress cracking and cleaving. The most common moonstone comes from the mineral adularia, named for an early mining site near Mt. Adular in Switzerland.