phengite
/ˈfɛndʒʌɪt/noun
1A transparent or translucent kind of stone known to the ancient world, probably crystallized gypsum or alabaster. Now historical.
2 Mineralogy. A biaxial, typically silica-rich variety of muscovite; (also) specifically a dioctahedral, potassic, and often ferromagnesian mica having a dioctahedral crystal structure.
Origin
Early 17th century; earliest use found in Philemon Holland (1552–1637), translator. From classical Latin phengītēs (Pliny) from Hellenistic Greek ϕεγγίτης phengite, selenite, or crystallized gypsum from ancient Greek ϕέγγος light, lustre, moonlight (of uncertain origin) + -ίτης.