On this microphotography in plane polarised light (PPL) of a metapélite, micas and chlorite are abundant : muscovite (musc) is colourless , biotite (biot) is brown and chlorite (chl) is grey-green. Quartz (Q) is rare. Such a rock, rich in micas, is also called micaschist. (The short side of the photo is around 1 mm).
Under the microscope, muscovite and biotite are brightly coloured under crossed-polarised light. The quartz is white to black.
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