What is "fengite"

Fengite \Fen"gite\, n. (Min.) A kind of marble or alabaster, sometimes used for windows on account of its transparency.

n. (context mineral English) A transparent form of marble or alabaster, formerly sometimes used for windows.

Fengite is a translucent sheets of marble or alabaster used during the Early Middle Ages for windows instead of glass.

Fengite is also a variant spelling of phengite, the high silica muscovite variety.