Adular

Part of speech: noun

Definitions

1. A transparent, colorless or white variety of orthoclase feldspar, often found as gemstone-quality crystals in Alpine rock
2. A mineral form of potassium feldspar that occurs as clear, glassy crystals, named after the Adula range in Switzerland
3. Another name for adularia, a translucent feldspar mineral prized by collectors for its pearly sheen and crystal habit

Etymology: Moonstone's glow has a name: "adular" is a variety of feldspar, and its mineral name, adularia, comes from the Adula, a group of Alpine peaks in Switzerland's Lepontine Alps. Mineralogists named the stone after the place where fine specimens were found, so the word points to a mountain range rather than to any quality of the stone itself. The name is also linked to a visual effect. The soft, bluish sheen that drifts across a moonstone when it is turned in the light is called adularescence, a word built from adular with the suffix "-escence," meaning "beginning to show." The stone's shimmer is caused by light scattering within its internal layers, and the term describes that moving glow.