tourmaline

noun

a mineral of variable color that consists of a complex borosilicate and is valued as a gem when transparent and cut

Pronunciation: /ˈtʊɚ.mə.lɪn/ / /ˈtʊɚ.məˌlin/

Etymology: From French tourmaline, ultimately from Sinhalese තෝරමල්ලී (tōramallī, “carnelian”)

A 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.”
“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.)”
A transparent gemstone cut from it.