Biotite

Biotite--K(Mg,Fe)₃AlSi₃O₁₀(OH)₂--is a dark, iron-rich mica that has a monoclinic crystal system. The octahedral layer is entirely occupied by Mg²⁺ and Fe²⁺ and the mineral is therefore trioctahedral, since all octahedra are occupied. The source of the lattice charge is the presence of Al³⁺ in place of Si⁴⁺ in 1/4 of the tetrahedral sites. The interlayer potassium is neatly nested among 12 oxygens and 2 hydroxyl groups, half from each layer.

Highlighting Features

Click on the buttons below to highlight specific features.

Magnesium (Mg) atoms
Aluminum (Al) atoms
Silicon (Si) atoms
Oxygen (O) atoms
Iron (Fe) atoms
Potassium (K) atoms
Potassium (K) and nearest neighbors
Single potassium (K) and nearest neighbors (12 O and 2 OH^-)
All atoms

Distribution

Biotite occurs worldwide in granites, gabbros, schists, and gneisses.

Crystallographic Data

Reference

Brigatti, M. F., and P. Davoli. 1990. Crystal-structure refinement of 1M plutonic biotites sample M62 from a rock transitional between granitic and monzonitic in the Valle del Cervo pluton. American Mineralogist. 75:305-313

This page is part of the Virtual Museum of Minerals and Molecules. All rights reserved to the Minerals & Molecules Project. For further information about the CHIME plug-in, see the Chime Source and Reference Page.

Original release: 1 Oct 1998;