Biotite

Biotite is a common phyllosilicate mineral within the mica group. It is a dark-colored, sheet silicate characterized by its perfect basal cleavage, allowing it to be easily split into thin, flexible flakes. Biotite's color ranges from black to brown, often appearing with a slightly greenish or reddish hue due to variations in its iron content. Chemically, biotite is a complex silicate of potassium, aluminum, iron, magnesium, and hydroxyl groups [(K(Mg,Fe)3AlSi3O10(OH)2)]. It is a major constituent of many igneous and metamorphic rocks and provides valuable information about their formation and geological history. Its presence can indicate specific temperature and pressure conditions.

Biotite meaning with examples

• During the petrographic analysis of the granite sample, the presence of abundant biotite flakes was readily observable, imparting a dark color to the rock. The thin, flexible biotite sheets separated easily, revealing the mineral's perfect basal cleavage. Further study showed the chemical composition of the biotite and showed the sample was formed at a certain time.
• High-grade metamorphic rocks often display large crystals of biotite, formed under intense heat and pressure. The textural features and mineral assemblage, including the presence of biotite, aided in interpreting the rocks' geological history. The biotite flakes within the gneiss created a wavy pattern showing its stress history.
• The eruption of the volcano released a pyroclastic flow. The subsequent analysis of the volcanic rock, revealed the presence of biotite, indicating the magma's source and the processes it underwent. The biotite helped geologists to understand the past of this mountain as they analyzed other samples with similar characteristics.
• Weathering processes, such as hydrolysis, can alter biotite, causing it to decompose into other clay minerals. The weathering process broke down the biotite over time and the minerals that formed aided in understanding the area's soil composition. These soils that are made up of biotite have unique characteristics.
• The thin section under the polarized light microscope showed that the biotite crystals were aligned in a parallel orientation, reflecting the directional stress experienced during rock formation. This helped provide information on the environment in which the rock formed. Observing how biotite reflects light can further aid in the rocks study.