- A black, dark brown, or greenish black variety of mica, occurring in many igneous and metamorphic rocks.More example sentences
- 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.
mid 19th century: named after Jean Baptiste Biot (1774–1862), French mineralogist.
More definitions of biotiteDefinition of biotite in:
- The British & World English dictionary