Sentence:  Although there are dozens of different types of gems, among the best known and most important are .... (Common gem materials not addressed in this <WSD>article</WSD> include amber, amethyst, chalcedony, garnet, lazurite, malachite, opals, peridot, rhodonite, spinel, tourmaline, turquoise and zircon.) 
Meaning of the word marked with <WSD> tags:  A piece of nonfictional writing such as a story, report, opinion piece, or entry in a newspaper, magazine, journal, dictionary, encyclopedia, etc.