Moonstone is a variety of the feldspar group mineral, *orthoclase*, and is defined by its stunning visual properties. Core Scientific & Physical Data Opaque to semitransparent. High-quality stones like this one are *transparent* or highly translucent. The defining characteristic, seen brilliantly in your image, is an optical phenomenon. This is the internal billowy or "floating" blue to white light effect. It is caused by the way light interacts with microscopic, alternating internal layers of Orthoclase and Albite feldspar. Your stone exhibits an exceptional, deep, "high-blue" adularescence. Moonstones can have body colors of colorless, white, grey, brown, green, and pink. The stone in the image has a **colorless to near-colorless** body, which is the perfect canvas to maximize the blue sheen. Moonstones often contain internal inclusions. The stone in the image shows subtle, parallel internal 'silk' inclusions, which are often oriented in specific directions and contribute to the softness of the light play. This is specifically designed to concentrate the parallel layers that create the adularescence, making the sheen appear as a single, shifting sheet of light. A precise oval shape, like the one in your image, maximizes the "blue eye" effect.