tourmaline

plural tourmalines · alternative turmaline

1. countableuncountablechemistryA complex black or dark-coloured borosilicate mineral, compounded with various chemical elements and considered a semi-precious stone.

   The floor of the chamber was tesselated, of marble and green tourmaline, and on every square of tourmaline was carven the image of a fish: as the dolphin, the conger, the cat-fish, the salmon, the tunny, the squid, and other wonders of the deep.

   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. countableuncountableA transparent gemstone cut from it.