Definition

Noun: - A dark-colored, iron- and magnesium-rich mineral belonging to the mica group, commonly found in igneous and metamorphic rocks. It is characterized by its perfect basal cleavage, allowing it to be split into thin, flexible sheets.

Usage

Biotite is used as a specific geological term to identify a common rock-forming mineral. - The granite sample contained large, shiny flakes of biotite. - Biotite is often used by geologists to help determine the conditions under which a rock formed.

Advanced Usage

• In Petrology: Biotite's composition and stability are key indicators in classifying rocks and understanding their thermal history.
  • The presence of biotite in the schist suggests medium-grade metamorphism.
• In Weathering: Biotite is known to weather more readily than other micas like muscovite.
  • The biotite in the outcrop had altered to clay minerals.

Variants and Related Words

• Mica (n): The broader mineral group to which biotite belongs, all sharing a sheet-like silicate structure.
  • Common micas include muscovite and biotite.
• Phlogopite (n): A magnesium-rich mica similar in structure to biotite but typically lighter in color (yellowish-brown).
  • Phlogopite is often considered a magnesium-rich variety of biotite.

Synonyms

• Black mica: A common informal name for biotite, referring to its typical dark color.
  • The black mica visible in the rock is biotite.

Related Phrases and Terms

• Biotite gneiss: A type of metamorphic rock where biotite is a major constituent.
  • The hills are composed primarily of biotite gneiss.
• Biotite schist: A schistose metamorphic rock rich in biotite.
  • The sample was identified as a biotite schist due to its abundant mica flakes.

Noun

1. dark brown to black mica found in igneous and metamorphic rock