Zircon

n.
  1. (Min.) A mineral consisting predominantly of zirconium silicate (Zr2SiO4) 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.
  2. an imitation gemstone made of cubic zirconia.
    3. Zircon syenite ,
    a coarse-grained syenite containing zircon crystals and often also elæolite. It is largely developed in Southern Norway.