Rating
Name	Biotite (thin section)
Type	Mineral
Cleavage	One perfect cleavage
Colour and Pleochroism	Strongly colored brown, reddish brown, or brownish green in thin section; Stong pleochroism
Relief	moderately high positive relief
Form	Euhedral to anhedral grains, most commonly displays a tabular habit with a hexagonal cross section
Optical Orientation	Parallel and birds eye extinction
Twinning	Not common
Birefringence, δ	δ = 0.028 - 0.07; Interference colors up to the third order possible, although they may be masked by mineral's strong color
Optical Character	Biaxial(-)
2V	2Vx = 0 - 25°
Key Characteristics	Strong brown coloration and plechroism, birds eye and parallel extinction, and high birefringence are diagnostic
Photograph Comments	pic 1(left): plane polarized light, magnification 100x; pic 2(right): cross polarized light, magnification 100x, biotite grains in bottom right display maple wood texture of birds eye extinction, other minerals in photo are epidote, quartz and plagioclase
Hand Sample URL	http://digicon.athabascau.ca/u?/RM,96
Subject	Minerals; Rocks; Identification photographs; Geology;
Date	2009
Format	image/jpeg
Identifier	2009-rm-0003
Collection Title	Rock and Mineral Samples
Repository	AU Digital Library
Rights	Subject to the Copyright Act

Biotite (thin section)

Description