Olivenite

Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Basic copper arsenate
Chemical Formula: Cu2(AsO4)(OH)
Method(s) of Verification: Gwaith-yr-Afon Mine - XRD at the Natural History Museum, London; Dolyhir Quarry - XRD at Manchester Museum and WDS at the Open University (analyses OU P202-P204, P377-P380).

Chemical Group:

  • Arsenates

Geological Context:

  • Supergene: in situ natural oxidation & weathering deposits
Introduction: olivenite is a supergene mineral that is typically encountered in the oxidized zones of chalcopyrite and arsenopyrite-bearing hydrothermal veins, but can occur in any type of weathered copper-arsenic-bearing primary association. It is usually accompanied by other arsenates such as clinoclase, tyrolite, chalcophyllite, scorodite and pharmacosiderite.
Occurrence in Wales: only discovered in very small quantities in Wales. Olivenite is currently known from two localities. This is in stark contrast to some other UK mining districts - such as Cornwall, where it is widespread and common at some localities. This perhaps reflects the paucity of arsenic/copper-bearing mineral veins with well-developed oxidation zones in Wales.

Key Localities:

  • Dolyhir Quarry, Old Radnor, Powys: olivenite formerly occurred relatively commonly as sprays of minute pale green acicular crystals associated with azurite, tyrolite and zincolivenite. The occurrence was hosted by barite-calcite veins surrounding a large sulphide vein outcropping in Wenlock Limestone which was exposed at the quarry in the mid-1990s. The locality has since been quarried away but specimens have been preserved in the National Museum of Wales Collection (Cotterell et al., 2011).
  • Gwaith-yr-Afon Mine, Goginan, Ceredigion: two specimens of olivenite have been found at this locality, better known for the more conspicuous occurrence of tyrolite. It occurs as the white variety (known as "leucochalcite"), forming silky-textured radial crystal groups to 0.75 mm in diameter covering areas to a square centimetre or so on goethite-coated quartz (Rust & Mason, 1994).

There are no key localities for this specimen.

References:

  1. Cotterell, T.F., Green, D.I., Hubbard, N., Mason, J.S., Starkey, R.E. and Tindle, A.G., 2011. The Mineralogy of Dolyhir Quarry, Old Radnor, Powys, Wales. UK Journal of Mines and Minerals, 32, 5-61.
  2. Rust, S.A. & Mason, J.S., 1994. An unusual occurrence of arsenate minerals at Gwaith-yr-Afon mine, Dyfed, Wales. Journal of the Russell Society, 5(2), 109-113.

There are no references for this specimen.