Minium

Crystal System: Tetragonal
Status of Occurrence: Unconfirmed Occurrence
Distribution: Rare
Chemical Composition: Lead oxide
Chemical Formula: Pb22+Pb4+O4
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:

  1. Greg, R.P. & Lettsom, W.G., 1858. Manual of the Mineralogy of Great Britain and Ireland. John van Voorst, London, 483pp.
  2. Hall, T.M., 1868. The Mineralogists' Directory. London, 168pp.
  3. 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.