Biotite

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.