Sterling Silver 925 Moonstone Ring Size 6.75 Moonstone is part of the mineral family of feldspars. It's an opalescent stone that can be found in colorless form as well as peach, pink, green, gray, yellow, brown, and blue. The play of light seen in Moonstone is called adularescence, and its clarity ranges from transparent to opaque. Chemical formula: (Na,Ca)Al₁₋₂Si₃₋₂O₈, KAlSi₃O₈