Vanadinite

Crystal System: Hexagonal
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Lead vanadate chloride
Chemical Formula: Pb5(VO4)3Cl
Method(s) of Verification: Tŷ Coch - reflected light microscopy & chemical analyses (Criddle & Symes, 1977); Dolgellau Gold-Belt - unrecorded

Geological Context:

  • Supergene: in situ natural oxidation & weathering deposits
Yellow vanadinite crystal fragments in manganese ore from T? Coch, Porthcawl. National Museum of Wales Collection (NMW 87.73G.M.) Photo D.I. Green, © National Museum of Wales.
Introduction: vanadinite is a member of the apatite group, and is similar in appearance to pyromorphite and mimetite. It occurs typically in the oxidized zone of lead-bearing mineral deposits. Fine crystallized specimens are known from many mines in Arizona, U.S.A and recently from Morocco.
Occurrence in Wales: there are very few records of vanadinite from Wales, largely due to the scarcity of vanadium in Welsh ore deposits. Criddle & Symes (1977), produced the only detailed account of vanadinite from the principality, describing the unusual mineralogy of Tŷ Coch manganese mine in South Wales. Later, in 1994, Bevins noted a specimen of vanadinite from ‘near Dolgelly’ in the NHM mineral collections. Unfortunately no more accurate provenance can be made than that it is likely to have been collected from one of the gold mines in the Dolgellau Gold-Belt given, the association with native gold.

Key Localities:

  • Dolgellau Gold-belt, Gwynedd: Bevins (1994) records that small brown hexagonal prisms of vanadinite occur associated with gold on NHM specimen no. B.M. 67960, labelled as from 'mines near Dolgelly'.
  • Tŷ Coch, near Porthcawl, South Wales: Criddle & Symes (1977) describe five types of ore material from Tŷ Coch. Vanadinite is recorded from three of these, each occurring in a different habit: vanadinite and pyrobelonite and intergrowths of the two are minor constituents of a massive, fine grained, compact, very hard, dark grey manganese ore with abundant lenticular masses of varicoloured calcite and barite. Vanadinite within this ore is typically pale lemon yellow, brittle and with no detectable cleavage; grey, somewhat greasy looking vanadinite fills small (5 mm) cavities within massive psilomelane with wad, infilling cavities and replacing limestone; ‘breccia ore’ consisting of goethite, minor hematite, quartz, and limestone fragments occasionally has small encrustations of bright yellow, powdery vanadinite.

There are no key localities for this specimen.

References:

  1. Bevins, R.E., 1994. A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
  2. Criddle, A.J., & Symes, R.F., 1977. Mineralization at Tŷ Coch, Glamorgan (Mid Glamorgan), Wales: the second occurrence of pyrobelonite. Mineralogical Magazine, 41, 85-90.

There are no references for this specimen.