Sentence:  Although there are dozens of different types of <WSD>gems</WSD>, 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. 
Meaning of the word marked with <WSD> tags:  A precious stone, usually of substantial monetary value or prized for its beauty or shine.