Noun
Mica containing iron and magnesia, generally of a black or dark green color; -- a common constituent of crystalline rocks. See Mica.
Source: Webster's dictionaryA considerable amount of mica (both muscovite and biotite) is often simultaneously formed, and the resulting product has a close resemblance to many kinds of schist. Source: Internet
A granite containing both muscovite and biotite micas is called a binary or two-mica granite. Source: Internet
Biotite is also useful in assessing temperature histories of metamorphic rocks, because the partitioning of iron and magnesium between biotite and garnet is sensitive to temperature. Source: Internet
Because argon escapes readily from the biotite crystal structure at high temperatures, these methods may provide only minimum ages for many rocks. Source: Internet
Cleavage, parting, fracture, and tenacity main Perfect basal cleavage as seen in biotite (black), and good cleavage seen in the matrix (pink orthoclase ). Source: Internet
In rhyolites and trachytes, early crystals of hornblende and biotite may be found in great numbers partially converted into augite and magnetite. Source: Internet