Definition of biotite in English:



mass noun
  • A black, dark brown, or greenish black micaceous mineral, occurring as a constituent of many igneous and metamorphic rocks.

    • ‘In most of the intrusion, hornblende and biotite are both present, but occasionally either may constitute the sole mafic phase.’
    • ‘Although dark minerals such as biotite and hornblende are usually present, giving the rock a speckled appearance, they are never abundant.’
    • ‘These microfaults are commonly pulled apart with growth of new quartz and biotite between pulled apart feldspar and hornblende.’
    • ‘Quartz, feldspar, white mica and biotite are all major constituents.’
    • ‘All four samples are medium-grained, and comprise variable proportions of hornblende, feldspar and quartz with accessory biotite and titanite.’


Mid 19th century: named after J.-B. Biot (1774–1862), French mineralogist.