A mineral, BaSO4, which may form a solid solution series with celestite (SrSO4); sp. gr. 4.3–4.6; hardness 3.0–3.5; orthorhombic; colourless to white, often tinged yellow, brown, blue, green, and red; white streak; vitreous lustre; crystals commonly tabular, prismatic, but can be fibrous, lamellar, and often granular; cleavage perfect {001}, present {210}, {010}. Occurs as a vein filling, as a gangue mineral with ores of lead, copper, zinc, silver, iron, and nickel, associated with calcite, quartz, fluorite, dolomite, and siderite, and as a low-temperature mineral which also occurs as a replacement for limestone, and as a cement in sandstone. Insoluble in acid. It is used as a weighting agent in drilling muds, in the chemical industry, in the manufacture of rubber, paper, and high-quality paints, and as an X-ray absorbent.