Abstract
CaSO4 has been investigated at room temperature over the pressure range of 0 to 160 kbar. A reversible, sluggish transition that occurs at about 20 kbar with a volume change of about 4% has been confirmed. The x-ray powder data collected at pressure can be indexed on the monoclinic monazite structure cell (P21/n) which is considered to be the most likely model structure for the new HP CaSO4 phase. The transition is largely distortional and involves rotation and displacement, but essentially preserves the chains of edge shared CaO8(9) and SO4 polyhedra found in the orthorhombic anhydrite (Bbmm) structure.
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Borg, I.Y., Smith, D.K. A high pressure polymorph of CaSO4 . Contr. Mineral. and Petrol. 50, 127–133 (1975). https://doi.org/10.1007/BF00373332
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DOI: https://doi.org/10.1007/BF00373332