A black, dark brown, or greenish black variety of mica, occurring in many igneous and metamorphic rocks.‘Although dark minerals such as biotite and hornblende are usually present, giving the rock a speckled appearance, they are never abundant.’
- ‘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.’
- ‘These microfaults are commonly pulled apart with growth of new quartz and biotite between pulled apart feldspar and hornblende.’
- ‘In most of the intrusion, hornblende and biotite are both present, but occasionally either may constitute the sole mafic phase.’
Mid 19th century named after J.-B. Biot (1774–1862), French mineralogist.
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