Mineral SrSO₄ which may form a solid solution series with barite; sp. gr. 3.9–4.0; hardness 3.0–3.5; orthorhombic; faint blue to colourless, sometimes stained red; white streak; vitreous lustre; crystals normally very tabular, resembling barite, but can also occur fibrous and granular; cleavage perfect basal {001}, present {210}, {010}; often fluorescent; occurs in sedimentary rocks, particularly dolomites, as a cavity-lining in association with barite, gypsum, anhydrite, and halite, with gypsum and anhydrite in evaporite deposits, also as a gangue mineral in hydrothermal veins with galena and sphalerite, and it will form concretionary masses in clays and marls. It is the main ore mineral for strontium and strontium compounds.