Anhydrite

Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Calcium sulphate
Chemical Formula: CaSO4
Method(s) of Verification: Parys Mountain - optical properties (polarizing microscope).

Chemical Group:

  • Sulphates

Geological Context:

  • Hydrothermal: sedimentary exhalative deposits
Introduction: anhydrite occurs commonly as an evaporite mineral in arid regions; in situations where more moisture is present the hydrated sulphate gypsum is more likely to occur. Another setting in which anhydrite may occur is within syngenetic exhalative (Kuroko-type) sulphide deposits.
Occurrence in Wales: anhydrite is rare in Wales. It occurs on Parys Mountain, which is a modified syngenetic exhalative ore-deposit, while certain horizons in the Triassic of South Wales, such as near Sully in South Glamorgan, show replacement features indicating that evaporites, including anhydrite, were originally present (Tucker, 1977; Waters & Lawrence, 1987).

Key Localities:

  • Parys Mountain, Anglesey: anhydrite has been observed forming cores to voids in siliceous sinter from the Carreg-y-doll Lode zone (Pointon & Ixer, 1980).

There are no key localities for this specimen.

References:

  1. Pointon, C.R. & Ixer, R.A., 1980. Parys Mountain mineral deposit, Anglesey, Wales: geology and ore mineralogy. Transactions of the Institution of Mining and Metallurgy (Section B: Applied earth science), 89, B143-B155.
  2. Tucker, M.E., 1977. The marginal Triassic deposits of South Wales: continental facies and palaeogeography. Geological Journal, 12, 169-188.
  3. Waters, R.A. & Lawrence, D.J.D., 1987. Geology of the South Wales Coalfield, Part III, the Country around Cardiff. 3rd edition. Memoirs of the Geological Survey of England and Wales. Explanation of Sheet 263.

There are no references for this specimen.