A triclinic mineral, Al₂(F,OH)₂SiO₄; pseudo-orthorhombic; colorless to pale blue, pale yellow to pinkish-beige ("sherry" topaz); defines hardness 8 on the Mohs scale; in cavities in granites, granite pegmatites, and rhyolites, and in surrounding metamorphic rocks; may be of gem quality. Compare: false topaz; Scotch topaz; Spanish topaz.