Biotite

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Biotite refers to a broad category of black mica minerals that are frequently discovered in igneous and metamorphic rocks. Among them are annite, phlogopite, siderophyllite, fluorophlogopite, fluorannite, eastonite, and numerous other varieties. These diverse micas exhibit differing chemical makeup but share very similar physical properties due to their sheet silicate structure. The term "biotite" is commonly employed in professional settings and introductory geology classes since these minerals typically cannot be distinguished without utilizing optical, chemical, or X-ray analysis techniques.