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Barite [BaSO4]
Structure Orthorhombic
Space Group : Pnma (No. 62)
a=8.8840 Å, b=5.4580 Å, c=7.1530 Å
a=b=g=90.00
Z=4
Atomic Positional Parameters
Ba 4c 0.1846 0.2500 0.1581
S 4c 0.4370 0.7500 0.1914
O 1 4c 0.5878 0.7500 0.1062
O 2 4c 0.3192 0.7500 0.0515
O 3 8d 0.4186 0.9702 0.3190
Reference
AA Colville and K Staudhammer (1967) American Mineralogist, 52, 1877
Mineral Chemistry
Barite group minerals include the sulphates (SO42-) of barium (barite, or barytes), strontium (celestine) and lead (anglesite). The structure of barite has sulphate groups lying on a reflection plane; two oxygens of the sulphate group lie within this plane, and two oxygens are mirror images across it. Each barium atom is coordinated by twelve oxygen atoms belonging to seven separate sulphate groups.
Barite, the most common barium mineral, is abundant in moderate to low-temperature sulphide veins, being associated with fluorite, galena, pyrite, quartz, and carbonates.
The CHIME figure shows barium ions as large spheres to make clearer their coordination with the oxygens of the sulphate tetrahedra. The unit cell is outlined.