Zircon

A mineral occurring in tetragonal crystals, usually of a brown or gray color. It consists of silica and zirconia. A red variety, used as a gem, is called hyacinth. Colorless, pale-yellow or smoky-brown varieties from Ceylon are called jargon.

a common mineral occurring in small crystals; chief source of zirconium; used as a refractory when opaque and as a gem when transparent