What is biotite thin section?

Biotite is a common mineral in igneous and metamorphic rocks, with a chemical composition of potassium iron magnesium aluminum silicate hydroxide. In thin section, biotite appears as dark brown to black flakes with a metallic luster. It typically forms in thin, platy crystals, and has a perfect cleavage in one direction.

Biotite is a member of the mica mineral group, along with muscovite and phlogopite. It is commonly found in rocks such as granite, gneiss, and schist, where it can appear as isolated grains or as aggregates with other minerals.

Under cross-polarized light in a thin section, biotite exhibits strong pleochroism, meaning that it appears to change color depending on the orientation of the mineral under the microscope. Biotite also shows interference colors and extinction patterns that can be used to identify and differentiate it from other minerals.

Biotite is a valuable mineral for geologists and petrologists, as it can provide information about the conditions under which the rock formed, such as temperature, pressure, and mineral interactions. By studying biotite in thin section, researchers can gain insights into the geological processes that have shaped the Earth's crust.