Moonstone is a captivating gem variety belonging to the feldspar mineral group. Its unique visual characteristics have made it a sought-after adornment for centuries. Historically, its ethereal glow inspired beliefs that it was formed from solidified beams of moonlight. The gem’s beauty is rooted not in its color alone, but in the way it interacts with light.
The Unique Phenomenon of Adularescence
The most defining feature of moonstone is adularescence, its floating light effect or schiller. This phenomenon gives the stone a soft, billowy glow that appears to glide just beneath the surface as the gem is turned. Adularescence results from the stone’s internal microstructure, which is composed of alternating, microscopic layers of two feldspar minerals: orthoclase and albite.
When light penetrates the moonstone, it is scattered and diffused by these thin, stacked layers. The resulting shimmer is often blue or white, reminiscent of moonlight on water. The intensity and color of the glow relate directly to the thickness of these mineral layers. Thinner layers produce the rare and highly valued electric blue sheen, while thicker layers result in a whiter or creamier adularescence.
Common Body Colors and Transparency
While the floating glow is the main attraction, the stone’s body color—the background hue—is also important. Moonstone’s base color, visible when adularescence is minimal, ranges widely from colorless to various muted tones. Common body colors include white, creamy yellow, tan, and shades of gray or brown.
The clarity of the material is a significant factor in its appearance and value. Moonstone typically ranges from semitransparent to fully opaque. The highest quality specimens are nearly transparent, allowing the adularescence to appear vivid and mobile. Lower-grade stones are often milky or opaque, which makes the schiller less defined and more static.
Popular Varieties and Types
Beyond the classic colorless or white stones, several commercially popular varieties feature distinct body colors or unique optical effects. Blue Moonstone is the most prized variety, characterized by a near-colorless, highly transparent body that showcases a strong, vivid blue adularescence. This rare stone has a fragile structure that requires careful handling during cutting.
Rainbow Moonstone is another sought-after type, though it is technically a variety of labradorite, a different feldspar mineral, and not true orthoclase moonstone. It is known for flashing an array of colors, including blue, yellow, and purple, due to a phenomenon called labradorescence. Peach or Pink Moonstone exhibits a warm body color that can range from soft pink to honey-orange.
Identifying Authentic Moonstone
Identifying a genuine moonstone relies on observing its unique optical and physical properties, particularly when compared to common imitations like glass or synthetic spinels. A real moonstone displays a dynamic adularescence that shifts and moves across the surface as the stone is gently tilted. Fakes often show a static, uniform flash or an overly bright, glassy sheen that does not float.
Natural stones frequently contain minor internal flaws, such as tiny stress cracks that gemologists describe as “centipedes.” If a stone appears flawless and perfectly transparent, it may be a glass imitation, as even the best natural moonstone retains some internal character. A genuine moonstone will also feel cool to the touch and warm up slowly, unlike glass or resin imitations which heat up much faster.