It is the name of a
group of minerals such as biotite, muscovite, lepidolite, zinnwaldite,
phlogopite and clintonite.
Muscovite and biotite
are the most common ones and also most prefect when it comes to the
cleavage of mica sheets.
light-coloured mica. It is most often grey, white or colourless, but
can be pinkish, or have green, yellow, violet, red or brown shades. Its
crystals are pseudohexagonal and tabular, and it has got the perfect
mica cleavage - it splits easily into thin sheets.
dark-coloured equivalent. Like muscovite, it has tabular
pseudohexagonal crystals, and the micaceous cleavage which
it to break into thin sheets. It is most often dark brown, but can be
black, dark green or reddish brown. Both are found in igneous,
metamorphic, and sedimentary rocks.