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Biotite - Mineral Properties and Uses

What is Biotite?

Biotite is a common rock-forming mineral. It is a mica found in many types of igneous rocks and in some metamorphic rocks. It is easily recognized because of its perfect cleavage that allows it to separate into thin, black, flexible sheets.

Uses

Biotite has very limited commercial use. Biotite particles are sometimes used as a surface treatment in decorative concrete, plaster and other construction materials. It is also used in the potassium-argon method for dating igneous rocks.

Color

black, dark green, dark brown

Streak

white to gray

Luster

vitreous

Diaphaneity

transparent to translucent

Cleavage

basal, perfect

Hardness

2.5 - 3

Specific Gravity

2.7 - 3.3

Distinguishing
Characteristics

dark color, perfect cleavage

Crystal System

monoclinic

Chemical Classification

silicate

Chemical Composition

K(Mg,Fe)3(Si3Al)O10(OH,F)2

Biotite Pictures

biotite
Biotite from Bancroft, Ontario, Canada.
Specimen is approximately 4 inches (10 centimeters) across.

beryl
Biotite from Bancroft, Ontario, Canada.
Specimen is approximately 4 inches (10 centimeters) across.

beryl
Cut biotite from Bancroft, Ontario, Canada.
Specimen is approximately 4 inches (10 centimeters) across.

beryl
A side view of biotite from Bancroft, Ontario, Canada.
Specimen is approximately 3/8 inch (.95 centimeter) thick.




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