Mineral Database

Mineral Database
Mineralogy of Wales

Minium

Crystal System: Tetragonal
Formula: Pb22+Pb4+O4
Status of Occurrence: Unconfirmed Occurrence
Distribution: Rare
Chemical Composition: Lead oxide
Method(s) of Verification: the techniques used for these early identifications are unknown. Therefore the validity of these reports are questionable.
Chemical Group:
  • Oxides & Hydroxides
Geological Context:
  • Supergene : in situ natural oxidation & weathering deposits
Introduction: minium is a rare product of the oxidation of lead-bearing minerals, in particular galena.
Occurrence in Wales: all records of minium from Wales are pre-20th Century including, an account from Anglesey by Greg & Lettsom (1858). The same authors also list minium from Merionethshire without description. Later Howard (1899) described minium from lead-bearing veins in the Carboniferous Limestone of South Wales. However, no examples of specimens are known. Therefore, minium has to be regarded as a dubious Welsh mineral species.
Key Localities:
  • Cefn Onn, South Wales: from lead bearing veins cutting Carboniferous Limestone exposed 'about a quarter of a mile west of the Rhymney tunnel' (Howard, 1899).
  • Merionethshire: listed as occurring in this county by both Greg & Lettsom (1858) and Hall (1868), but without description.
  • Parys Mountain, Anglesey: described by Greg & Lettsom (1858) as “in veins of clay-slate with galena” from Anglesey. Hall (1868) lists minium as occurring at Pary’s Mine, presumably referring to the same occurrence. Unfortuately no specimens are known, to confirm either account.
References:
  • Greg, R.P. & Lettsom, W.G., 1858 Manual of the Mineralogy of Great Britain and Ireland.  John van Voorst, London, 483pp.
  • Hall, T.M., 1868 The Mineralogists' Directory.  London, 168pp.
  • Howard, F.T., 1899 Note on the lead deposits of the eastern fringe of the South Wales Coalfield.  Transactions of the Cardiff Naturalists' Society, 30, 46-47.