(Mg,Fe)Al₂(OH)₂(PO₄)₂ A violet-blue or azure-blue mineral with vitreous luster; composed of basic aluminum phosphate and occurring in small masses or monoclinic crystals; hardness is 5-6 on Mohs scale, and specific gravity is 3.06-3.12. Also known as berkeyite; blue spar; false lapis.