Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Strontium sulphate
Chemical Formula: SrSO4
Method(s) of Verification: Barry Island - XRD at the National Museum of Wales (X-ray numbers NMW X-778, 780 & 785); Penarth Head - XRD (NMW X-789 & 790).
Bladed, pale blue crystals of celestine in nodule from Triassic marls, Barry Island. Specimen National Museum of Wales (NMW 61.152.GR.5), photo M.P. Cooper, © National Museum of Wales.
Introduction: celestine is frequently found in sedimentary rocks, and especially in red-bed sequences, where it forms bed and nodules. It also occurs in hydrothermal veins, in particular in those of the Mississippi Valley type, where it may be associated with calcite, baryte, galena and sphalerite. When massive, celestine is difficult to distinguish from baryte, which is of a similar appearance, hardness and density. Furthermore, celestine actually forms a series with baryte, and many examples are known in which a composition intermediate between the two is present. Such material is often referred to as barytocelestine, however this is not a valid mineral species.
Occurrence in Wales: the first record of celestine in Wales was by Conybeare and Phillips (1822), who reported the presence of 'geodes filled with sulphate of Strontian' from Barry Island in South Glamorgan. In addition, Howard (1895) recorded the variety barytocelestine from Barry, where fine tabular blue crystals were recovered during the excavations for the docks. He also noted the presence of thin, fibrous barytocelestine veins cutting Carboniferous Limestone on Barry Island. Since that time, a number of other localities have been discovered, with the best specimens being found after cliff-falls in the mid-1990s between Penarth and Lavernock.
- Barry Island, South Wales: the localities mentioned in the introductory section are no longer accessible, but celestine is clearly widespread on the island, making any temporary exposures created in future worth checking. Specimens are held in the National Museum of Wales Collection.
- Llantrisant area, South Wales: Thomas (1968) described celestine as compact to granular masses occurring in geodes and nodules in the Triassic Dolomitic Conglomerate, exposed in road cuttings during the construction of the Llantrisant bypass. However, later studies (Bowler & Kingston, 1971; Alabaster, 1990) failed to detect any.
- Penarth and Lavernock, South Wales: celestine occurs in veins occupying small faults cutting Rhaetic strata along the coastal section from Penarth Head to Lavernock Point. Material is only available following cliff-falls. The veins are dominated by fibrous white, pinkish or bluish celestine and calcite; occasional cavities contain well-formed tabular white to rich blue celestine crystals. Superb specimens were collected in 1995-6 following a cliff-fall between Penarth and Lavernock: these surpass the historical Barry Docks material in quality (I.E. Jones Collection). Celestine is also present as small bladed crystals associated with calcite, occupying the body chambers of ammonites and other fossils in the overlying Lower Lias (Bevins & Mason, 2000).
- Alabaster, C., 1990. Alstonite and barytocalcite from Llantrisant, South Wales and barytocalcite from Holwell, Mendip Hills, England. Journal of the Russell Society, 3, 1-6.
- Bevins, R.E. & Mason, J.S., 2000. Welsh Metallophyte and metallogenic evaluation project: Results of a Minesite Survey of Glamorgan and Gwent. National Museums & Galleries of Wales, Cardiff
- Bowler, C.M.L. & Kingston, G.A., 1971. Mineralisation in the Triassic rocks of the Llantrisant area, Glamorgan. 1970 Gregynog Mineral Exploitation Colloquium Report. University College Cardiff, 30-34.
- Conybeare, W.D. & Phillips, W., 1822. Outlines of the geology of England and Wales. W. Phillips, London, 471pp.
- Howard, F.T., 1895. The geology of Barry Island. Transactions of the Cardiff Naturalists' Society, 27, 42-55.
- Thomas, T.M., 1968. A new occurrence of celestite, near Llantrisant, Mid Glamorgan. Geological Magazine, 105, 185-186.