Moonstone is a captivating gemstone, a variety of the feldspar mineral group. Its allure stems from a distinctive optical effect that gives it an ethereal glow, reminiscent of moonlight.
The Primary “Color”: Adularescence
The defining visual characteristic of moonstone is adularescence, an optical phenomenon. This effect manifests as a soft, shimmering light that appears to glide across the gem’s surface. Adularescence creates the illusion of an internal glow, often appearing milky white or bluish, and is considered the moonstone’s signature “color.” It is not a fixed body color but rather a mobile sheen that billows just beneath the stone’s surface as it is rotated. This captivating light play gives moonstone its name, evoking the soft luminescence of moonlight on water.
Adularescence distinguishes moonstone from many other gemstones. The intensity and color of this shimmering effect can vary, with some moonstones displaying a vivid blue flash that is highly prized.
Beyond the Shimmer: Moonstone’s Color Spectrum
While adularescence is the hallmark, moonstones also exhibit a range of underlying body colors. The most prized moonstones typically have a colorless or nearly transparent body that allows the adularescent effect to stand out prominently. However, the gem can also be found in various subtle hues.
Common body colors include white, grey, peach, pink, yellow, and even green or brown. Peach moonstone, for instance, displays warm orange to yellow tones. A distinct variety often marketed alongside moonstone is “rainbow moonstone,” which is actually a type of labradorite. This plagioclase feldspar exhibits a multicolored adularescence, including flashes of blue, purple, green, and yellow.
Factors Influencing Moonstone’s Appearance
The unique visual properties of moonstone arise from its geological composition and structure. Moonstone is composed of two intergrown feldspar minerals, orthoclase and albite. During their formation, these minerals separate into microscopic, alternating layers, creating a layered structure within the stone.
Adularescence occurs when light enters the moonstone and is scattered and diffracted by these thin, stacked layers. The thickness and arrangement of these internal layers influence the intensity and color of the adularescent flash. Thinner layers tend to produce a more intense blue flash, while thicker layers typically result in a whiter or creamier glow. Beyond adularescence, trace elements or mineral inclusions contribute to its various body colors, such as iron or copper leading to shades of peach, green, or brown.