Mica, Biotite

This is one of the mica minerals common in the sand from the Palm Desert area. This grain has a 2V of about 0 degrees.

Transmitted Circular Polarized Light

Definition/Function:

Biotite is a sheet silicate with the general chemical composition indicated as
K₂(Mg,Fe²⁺)_6-4(Fe³⁺,Al,Ti) _0-2[(Si_6-5Al_2-3)O₂₀](OH,F)₄. It is a very common mineral.

Significance in the Environment:

Characteristic Features:

Biotite is dark green or Brown most often in thin section, has a 2V of 0-15 degrees, a birefringence of about 0.001 when view normal to its perfect cleavage plane, and has a negative optical sign. Biotite is the more iron-rich part of the phlogopite-biotite series. With more titanium the crystal becomes more reddish.

Associated Particles:

References:

Deer, W. A., R. A. Howie, and J. Zussman, AN INTRODCUTION TO THE ROCK-FORMING MINERALS, ISBN 0-582-30094-0, pp. 298-307, 1992.