Sentence:  Although there are dozens of different types of gems, among the best known and most important are [...]&thinsp;. (Common gem materials not addressed in this article include amber, amethyst, chalcedony, garnet, lazurite, <WSD>malachite</WSD>, opals, peridot, rhodonite, spinel, tourmaline, turquoise and zircon.) 
Meaning of the word marked with <WSD> tags:  A bright green mineral, a basic copper carbonate, Cu<sub>2</sub>CO<sub>3</sub>(OH)<sub>2</sub>; one of the principal ores of copper.