Fengite is a transparent form of marble or alabaster. In former times it was sometimes used for windows instead of glass. Fengite is also a variant spelling of phengite, the high silica muscovite variety. ...
• (n.) A kind of marble or alabaster, sometimes used for windows on account of its transparency.
Fen'gite noun (Min.) A kind of marble or alabaster, sometimes used for windows on account of its transparency. 
Fengite is a kind of marble or alabaster, formerly sometimes used for windows on account of its transparency.