Hydrowoodwardite

Crystal System: Hexagonal
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Copper aluminium sulphate hydroxide hydrate
Chemical Formula: Cu1-xAlx(OH)2(SO4)x/2(H2O)n, with x < 0.67 and n ≥ 3x/2
Method(s) of Verification: Ffriddgoch Mine - XRD (Raade et al., 1985) on NMW specimen NMW 27.111.GR.464; Simdde Dylluan - XRD & Infra-red spectra (Nickel, 1976), XRD (Raade et al.,1985) on NMW specimen NMW 27.111.GR.463.

Chemical Group:

  • Sulphates

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
Introduction: hydrowoodwardite is a secondary copper mineral which forms porous crusts on plant remains and on rock fragments associated with near surface copper mineralization. It was described as a new mineral species in 1996 and is considered to be the copper-dominant analogue of glaucocerinite and carrboydite (Mandarino, 2001).
Occurrence in Wales: so-called woodwardite from two localities in North Wales was shown, by Raade et al. (1985) to be the Cu-analogue of glaucocerinite, following the discovery by Nickel (1976) that alleged woodwardite from Carnarvonshire was distinctly different to woodwardite from the type locality in Cornwall. Hydrowoodwardite is identical to Nickel’s (1976) incompletely described mineral from Carnarvonshire (Mandarino, 2001). Therefore, the majority of woodwardite occurrences in Wales are actually hydrowoodwardite.

Key Localities:

  • Ffridd-Goch Mine, Llanfachreth, Gwynedd: powdery pale green efflorescence coating the underside of bracken leaves on National Museum of Wales specimen NMW 27.111.GR.464.
  • Simdde Dylluan, Drws-y-coed, Nantlle, Gwynedd: glossy (NMW 27.111.GR.462) to powdery (NMW 27.111.GR.461) pale green flowstone encrusting fragments of rock and vegetation (grass – NMW 27.111.GR.463).

References:

  1. Mandarino, J.A., 2001. New Minerals 1995-1999. The Canadian Mineralogist Special Publication 4. 281 pp.
  2. Nickel, E.H., 1976. New data on woodwardite. Mineralogical Magazine, 40, 644-647.
  3. Raade, G., Elliott, C.J., & Din, V.K., 1985. New data on glaucocerinite. Mineralogical Magazine, 49, 583-590.