Biotite Under Thin Section

Basal sections of biotite in thin section are typically approximately hexagonal in shape and usually appear isotropic under cross polarized light.

Biotite under thin section. Under cross polarized light the biotite thin section appears darker brown in areas as well as a pink yellow color in others. Under cross polarized light biotite exhibits extinction approximately parallel to cleavage lines and can have characteristic bird s eye extinction a mottled appearance caused by the distortion of the mineral s flexible lamellae during grinding of the thin section. To link to this object paste this link in email im or document to embed this object paste this html in website.

Biotite thin section view description. Add tags comment rate. Biotite is a solid solution between the end members phlogopite kmg 3 alsi 3 o 10 oh 2 and annite kfe 3 alsi 3 o 10 oh 2 although pure annite does not occur in nature.

The colourless inclusions in the basal section are apatite. Note the presence of the one perfect cleavage on the c axis parallel section and its absence on the basal section. Above the same group of crystals under crossed polars.

C axis parallel section left and subhedral basal section right of brown biotite. In addition small amounts of na rb cs and ba may substitute for k and like in other minerals f can substitute for oh and increase the stability of biotite to higher temperatures and pressures. Biotite usually dark green brown or black has a pale brown color under plane polarized light in this sample.

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