Ktenasite

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Copper zinc sulphate hydroxide hydrate
Chemical Formula: (Cu,Zn)5(SO4)2(OH)6.6H2O
Method(s) of Verification: Ystrad Einion Mine - XRD (Natural History Museum, London).

Chemical Group:

  • Sulphates

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
  • Supergene: in situ natural oxidation & weathering deposits
Introduction: ktenasite is an extremely rare secondary mineral that forms in the oxidized zone of copper- and zinc-bearing ore deposits and within post-mining environments.
Occurrence in Wales: ktenasite forms part of the post-mining suite of supergene secondary minerals discovered within broken veinstone used as backfill, underground in Ystrad Einion Mine and reported by Mason & Rust (1997). Similar environments have been observed at a number of mines in the Central Wales Orefield, but ktenasite remains illusive to all but that one locality.

Key Localities:

  • Ystrad Einion Mine, Furnace, Ceredigion: several crystal forms have been observed. All are relatively rare, derived from low-grade sulphide ore dominated by chalcopyrite, with minor galena and sphalerite, in a quartz gangue containing ferroan dolomite which has reacted with mine water in a short backfilled passage. Sulphides have dissolved and secondary minerals precipitated out within cavities in corroded ferroan dolomite. Parallel groups of thin, pale, emerald-green bladed crystals to about 3 mm in association with serpierite and gypsum have been identified at Oxford University Museum and a more typical tabular crystal form has been identified at the Natural History Museum, London. Further to this corroded lenticular crystals to 0.7 mm on joints in silty sandstone have also been identified as ktenasite (Mason & Rust, 1997).

References:

  1. Bevins, R.E., 1994. A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
  2. Mason, J.S. & Rust, S.A., 1997. The Mineralogy of Ystrad Einion Mine, Dyfed, Wales. U.K. Journal of Mines and Minerals, 18, 33-36.