Biotite and muscovite are aluminum-containing silicates which cleave in thin sheets and are called micas. Biotite has the general formula (K(Mg,Fe)3(AlSi3O10)(OH)2) . The presence of iron and magnesium in biotite makes it darker in color than muscovite. With a higher crystallization temperature, biotite is viewed as occurring earlier in the Bowen reaction series.

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