Biotite

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Plane-Polarized Light

Crossed Polarizers


Biotite in plane polarized light. This biotite is very green. Note the mottled texture.

BI-P1.JPG (74425 bytes)

Same field in crossed polarizers. The appearance is dominated by the deep color and changes little.

BI-X1.JPG (71280 bytes)

BI-P2.JPG (64410 bytes) Plane polarized light. This biotite is very pleochroic and changes color from light greenish brown to nearly opaque.

A plane polarized light view of biotite ranging from light yellow-green to dark green in color. Note the good cleavage.

BI-P3.JPG (57151 bytes)

Same field in crossed polarizers. Light biotite grains can show appreciable interference color.

BI-X3.JPG (63199 bytes)

Biotite is often brown. The specimen below, seen in plane polarized light, ranges from light tan to red-brown in color. Numerous pleochroic haloes around small zircon inclusions can be seen.

BI-P4.JPG (65110 bytes)

Same field in crossed polarizers. This relatively light biotite shows obvious second-order colors, though somewhat modified by the natural color.

BI-X4.JPG (86440 bytes)

The two specimens below show biotite of different shades dotted with numerous dark haloes around zircon inclusions.

BI-P5.JPG (61274 bytes)

BI-P6.JPG (51361 bytes)


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Created 22 Sept 1997, Last Update 16 December 1999

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