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Crystal System: Tetragonal
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Calcium molybdate
Chemical Formula: CaMoO4
Method(s) of Verification: Benallt Mine - XRD and EDS at Manchester Museum (Dossett et al., 2007).

Chemical Group:

Geological Context:

Creamy-white powellite microcrystals (to 0.4 mm on edge) from Benallt Mine. I. Dossett specimen. Photo D.I. Green, © D.I. Green.
Introduction: an uncommon secondary species formed by the alteration of molybdenite or other molybdenum-bearing minerals, but can also form in low-temperature hydrothermal environments, such as with zeolites in vugs in basalt and within skarns and contact metamorphic environments.
Occurrence in Wales: Dossett et al. (2007) described the first and only occurrence of powellite in Wales from a single specimen collected at Benallt Mine, near Rhiw, Pen Llyn in 2006. One small (5 mm across) cavity within a specimen of altered igneous rock was discovered to contain twenty microcrystals of powellite.

Key Localities:


  1. Dossett, I., Green, D.I. and Cotterell, T.F., 2007. Powellite from Benallt mine, Lleyn Peninsula, Gwynedd: a first Welsh occurrence. Journal of the Russell Society, 10, 54-55.