'''Biotite''' is a common [[rock]]-forming [[mineral]] of the [[mica]] family. Biotite is a [[black]] or dark [[brown]] [[silica]]te rich in [[iron]], [[magnesium]], [[potassium]], [[aluminum]], and, of course, [[silica]]. Like other [[mica]]s, it forms flat book-like crystals that peel apart into individual sheets on cleavage planes.<ref>http://wrgis.wr.usgs.gov/docs/parks/misc/glossaryb.html</ref>
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[[Image:Biotite.jpg|thumb|300px]]'''Biotite''' is a common [[rock]]-forming [[mineral]] of the [[mica]] family. Biotite is a [[black]] or dark [[brown]] [[silica]]te rich in [[iron]], [[magnesium]], [[potassium]], [[aluminum]], and, of course, [[silica]]. Like other [[mica]]s, it forms flat book-like crystals that peel apart into individual sheets on cleavage planes.<ref>http://wrgis.wr.usgs.gov/docs/parks/misc/glossaryb.html</ref>