• (n.) A glassy colorless mineral occurring in rhombohedral crystals, sometimes used as a gem. It is a silicate of glucina, and receives its name from its deceptive similarity to quartz.
Phen'a·cite noun [ Greek ..., ..., impostor, deceiver.] (Min.) A glassy colorless mineral occurring in rhombohedral crystals, sometimes used as a gem. It is a silicate of glucina, and receives its name from its deceptive similarity to quartz. 
Beryllium orthosilicate