Tool for Microscopic Identification Home

 

Show UniqueIdentification

Id 22
Identification Type Mineral
Name Biotite
Distinguishing Features Flaky
Pseudo-isotropic
Pleochroic
bird's-eye-extinction
Description Occurs as flakes larger than surrounding material, green to brown transparent, may be pleochroic. Low to moderate relief. Cleavage planes frequently visible as platy layers. Classic bird's eye extinction (mottled, pebbly texture) not always present in smear slide. Very low apparent birefringence (pseudo-isotropy) because flakes settle with {001} in the plane of the slide. However, by tilting the slide very slightly (e.g., by slipping another slide under the slide) one can evaluate the true birefringence (thanks to Frank Brown, U. Utah, for the tip). Biotite has strong birefringence; chlorite, which may form as an alteration product or a metamorphic mineral, can look similar to biotite in plane light but has weak birefringence.
Tags brown
green
layers
ragged
silicate
mica
transparent
External Resources Biotite on MinDat
Imposters Chlorite
Biotite can be altered to Chlorite. Birefringence can be used to distinguish, but is not obvious when mica flakes settle on the slide with {001} parallel to the slide. To see birefringence colors, slightly incline the slide by slipping another slide under it. Biotite is strongly birefringent; chlorite weakly
Images
Unique Identification: Biotite
Site name: Big Soda
Light type: Plane-Polarized Light
Magnification: 400x
Submitted by: Amy Myrbo
Notes: calcite-inclusion,
Image Tags: none
Unique Identification: Biotite
Site name: Big Soda
Light type: Cross-Polarized Light
Magnification: 400x
Submitted by: Amy Myrbo
Notes: calcite-inclusion,
Image Tags: none
Unique Identification: Biotite
Site name: not specified
Light type: Plane-Polarized Light
Magnification: 400x
Submitted by: Amy Myrbo
Notes: none
Image Tags: none
Unique Identification: Biotite
Site name: not specified
Light type: Plane-Polarized Light
Magnification: 630
Submitted by: Michael Rosen Blas Valero
Notes: colored green platey heavy-mineral basal-section
Image Tags: none
Unique Identification: Biotite
Site name: not specified
Light type: Cross-Polarized Light
Magnification: 630
Submitted by: Michael Rosen Blas Valero
Notes: colored green platey heavy-mineral basal-section
Image Tags: none
Unique Identification: Biotite
Site name: not specified
Light type: Plane-Polarized Light
Magnification: not specified
Submitted by: Guy Rothwell
Notes: Large biotite mica flake, note the conspicuously large size of the flake compared with the associated material, flakes
Image Tags: none
Unique Identification: Biotite
Site name: not specified
Light type: Plane-Polarized Light
Magnification: not specified
Submitted by: Guy Rothwell
Notes: Field of brown and green mica flakes, pyroxene crystal fragments also in the field, pyroxenes crystal-fragment flakes
Image Tags: none
Unique Identification: Biotite
Site name: Bengal Fan, Indian Ocean ( 8 00.42 N, 86 16.97 E)
Light type: Plane-Polarized Light
Magnification: not specified
Submitted by: Guy Rothwell
Notes: Field of green and brown mica flakes, flakes
Image Tags: none
Unique Identification: Biotite
Site name: not specified
Light type: Plane-Polarized Light
Magnification: not specified
Submitted by: Guy Rothwell
Notes: Brown biotite mica flake, flakes
Image Tags: none
Unique Identification: Biotite
Site name: not specified
Light type: Plane-Polarized Light
Magnification: not specified
Submitted by: Guy Rothwell
Notes: Large green biotite mica flake, flakes
Image Tags: none
Unique Identification: Biotite
Site name: Yellowstone
Light type: Plane-Polarized Light
Magnification: 400
Submitted by: Val Stanley
Notes: A thin book of biotite sheets, with torn edges
Image Tags: flaky brown
Unique Identification: Biotite
Site name: Reid Lake
Light type: Plane-Polarized Light
Magnification: 400
Submitted by: Val Stanley
Notes: Pleochroic halo from zircon in biotite; discoloration resulting from alpha particle irradiation
Image Tags: none
Unique Identification: Biotite
Site name: Ozera Karakul
Light type: Plane-Polarized Light
Magnification: 400
Submitted by: Val Stanley
Notes: vivid interference colors
Image Tags: none
Unique Identification: Biotite
Site name: Lake Malawi
Light type: Plane-Polarized Light
Magnification: not specified
Submitted by: Andy Breckenridge
Notes: biotite, volcanic
Image Tags: none
Unique Identification: Biotite
Site name: Lake Malawi
Light type: Cross-Polarized Light
Magnification: not specified
Submitted by: Andy Breckenridge
Notes: biotite, volcanic
Image Tags: none
Unique Identification: Biotite
Site name: not specified
Light type: Plane-Polarized Light
Magnification: not specified
Submitted by: not specified
Notes: none
Image Tags: reaction-texture
Unique Identification: Biotite
Site name: not specified
Light type: Cross-Polarized Light
Magnification: not specified
Submitted by: not specified
Notes: none
Image Tags: reaction-texture