Assortment of moonstones. Photograph by Joseph and Lillian Stachura at http://www.stachurawholesalegemstones.com/
Today’s gem is a demure and proper lady who is always in fashion and a favorite of royalty. The ancient Romans believed she was tangible moonlight and a protector. In India, moonstones were considered sacred, not offered for sale, and often displayed on yellow cloths, a sacred color. In Asia, spirits were believed to reside in the stones because of their internal blue shimmer. Moonstone is commonly considered a feminine stone, as well as one for new lovers and those seeking good fortune. A moonstone under the pillow is thought to bring dreams of the future.
Moonstone is composed of two feldspar species: orthoclase and albite. These form stacked layers through heating and cooling. Light scatters as it passes through the layers, leading to a phenomenon called adularescence. Thin layers create the blue shine, while thicker layers result in a milky haze. If the layers are arranged along a particular axis you get chatoyancy, or a cat’s eye effect.
Moonstones can be colorless, grey, green, yellow, pink, orange, or brown, depending largely on the iron content. While most of us think of pale, translucent moonstone cabochons, the finest moonstones are clear and can be faceted. Moonstone is a common gem and found worldwide, but the best material today comes out of Sri Lanka. Due to its fragile, layered nature at 6-6.5 Mohs, there are not many treatments used to enhance moonstone. Rainbow moonstone, an inexpensive but attractive mineral, is actually a form of Labradorite, a related feldspar out of India.