Crystal System: Tetragonal
Status of Occurrence: Confirmed Occurrence
Chemical Composition: Zirconium silicate
Chemical Formula: ZrSiO4
Method(s) of Verification: all occurrences - polarizing microscope; U-Pb dated zircons - EMPA.
- Sedimentary: allogenic (detrital)
Introduction: a common mineral in igneous rocks, particularly intermediate and acid compositions (rhyolite, dacite, granite & granodiorite) and pegmatites. It is also a common detrital mineral in sedimentary rocks.
Occurrence in Wales: zircon is an accessory mineral, forming a very minor component of igneous rocks. No large crystal or gem occurrence is noted from Wales. Recorded examples are typically less than 1 mm in length and therefore can be identified only with the aid of a petrological microscope. In recent years zircon samples from igneous rocks have been dated using U-Pb isotopes to provide the age of crystallization of the original magma (e.g. Tucker & Pharaoh, 1991; Horák et al., 1996; Compston et al., 2002). Studies of detrital minerals from sediments across Wales included descriptions of zircons (e.g. Heard 1922; Heard & Davies, 1923; Boswell, 1927; Griffiths & Stuart, 1940).
There are no key localities for this specimen.
- Boswell, P.G.H., 1927. On the distribution of purple zircon in British sedimentary rocks. Mineralogical Magazine, 8, 103-107.
- Compston, W., Wright, A.E. & Toghill, P., 2002. Dating the Late Precambrian volcanicity of England and Wales. Journal of the Geological Society, London, 159, 323-339.
- Griffiths, J.C. & Stuart, A., 1940. An occurrence of detrital diaspore in South Wales. Geological Magazine, 77, 74-76.
- Heard, A., 1922. The petrology of the Pennant Series, east of the River Taff. Geological Magazine, 59, 83-94.
- Horák, J.M., Doig, R., Evans, J.A. & Gibbons, W., 1996. Avalonian magmatism and terrane linkage: new isotopic data from the Precambrian of North Wales. Journal of the Geological Society, London, 153, 91-99.
- Tucker, R.D. & Pharaoh, T.C., 1991. U-Pb zircon ages for Late Precambrian rocks in southern Britain. Journal of the Geological Society, London, 148, 435-443.