Crystal System: Cubic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Thorium oxide
Chemical Formula: ThO2
Method(s) of Verification: Presteigne - EMPA (Parnell & Eakin, 1989)

Chemical Group:

  • Oxides & Hydroxides

Geological Context:

  • Sedimentary: diagenetic
  • Igneous
Introduction: thorite is a uranium oxide mineral that forms a series with uraninite. It is most commonly found within pegmatites.
Occurrence in Wales: there is just one reported occurrence of thorianite from Wales.

Key Localities:

  • Presteigne, Powys: thorianite, associated with thorite, has been identified as minute inclusions, 2-5 μm across, within spherical bitumen nodules in the Folly Sandstone, of Llandovery age, exposed in the Presteigne area of Powys (Parnell & Eakin, 1989). The nodules formed within the sediment although the source of the thorium is uncertain, a possible candidate being monazite nodules within the Ordovician and Silurian strata of the Welsh Basin.


  1. Parnell, J. & Eakin, P., 1989. Thorium-bitumen mineralization in Silurian sandstones, Welsh Borderland. Mineralogical Magazine, 53, 111-116.