A monoclinic mineral, K₂Mg₆(Si₆Al₂O₂₀)(F,OH)₄; a magnesium-rich end-member of the biotite crystal solution series; mica group; pseudohexagonal with perfect basal cleavage; occurs in crystalline limestones as a product of dedolomitization, in potassium2310 rich ultramafic rocks, as an alteration mineral in sulfur-rich hydrothermal assemblages, and in kimberlites.