zircon

plural zircons

1. uncountableA mineral occurring in tetragonal crystals, usually of a brown or grey colour and consisting of silica and zirconia.

   […] salamanders, mermaids, chimaeras, wild men o’ the woods, leviathans, all hewn from faultless gems, thrice the bulk of a big man’s body, velvet-dark sapphires, chrysolite, beryl, amethyst, and the yellow zircon that is like transparent gold.

   1922, E[ric] R[ücker] Eddison, The Worm Ouroboros: A Romance, London: Jonathan Cape […], →OCLC, page 3

   1 more example

   Although there are dozens of different types of gems, among the best known and most important are […]. (Common gem materials not addressed in this article include amber, amethyst, chalcedony, garnet, lazurite, malachite, opals, peridot, rhodonite, spinel, tourmaline, turquoise and zircon.)

   2012 March 28, Lee A. Groat, “Gemstones”, in American Scientist, volume 100, number 2, archived from the original on 14 Jun 2012, page 128

2. countableA crystal of zircon, sometimes used as a false or semiprecious gemstone.

   A zircon princess, seemed to lost her senses

   1982, “The Message”, performed by Grandmaster Flash and the Furious Five