Although there are dozens of different types of gems, among the best known and most important are diamond, ruby and sapphire, emerald and other gem forms of the mineral beryl, chrysoberyl, tanzanite, tsavorite, topaz and jade.
2012 March, Lee A. Groat, “Gemstones”, in American Scientist, volume 100, number 2, archived from the original on 14 June 2012, page 128