Sentence:  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 <WSD>mineral</WSD> beryl, chrysoberyl, tanzanite, tsavorite, topaz and jade. 
Meaning of the word marked with <WSD> tags:  Any naturally occurring inorganic material that has a (more or less) definite chemical composition and characteristic physical properties.