Mineral Database (Saesneg yn unig)

Mineral Database (Saesneg yn unig)
Mineralogy of Wales

Asbolane

Crystal System: Hexagonal
Formula: (Co,Ni)1-y(MnO2)2-x(OH)2-2y+2x.nH2O
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Cobalt nickel manganese oxide hydroxide hydrate
Method(s) of Verification: not known.
Chemical Group:
  • Oxides & Hydroxides
Geological Context:
  • Supergene : in situ natural oxidation & weathering deposits
Introduction: the name meaning 'to soil like soot', asbolane is a poorly-characterised earthy black mineral which is essentially a manganese 'wad' carrying variable, and occasionally economic, levels of cobalt and nickel. Asbolane typically occurs in oxide-dominated assemblages, formed by prolonged weathering processes.
Occurrence in Wales: although localities are few, thus giving an initial impression of rarity, asbolane occurs at one mine near Dyserth, Clwyd, in sufficient quantity that it was worked as a low-grade ore of nickel and cobalt in the late 19th Century (Le Neve Foster, 1882).
Key Localities:
  • Gwynedd: a zinc-bearing asbolane has been reported as concretionary deposits in "certain abandoned lead and zinc mines" in Gwynedd. They are apparently of abiotic origin, formed by autolytic oxidation (Roberts, 1986). The formula of this substance approximates to: Mn2.0-2.6Zn0.91-1.8O4.1-5.3(OH)1.6-3.4.(H2O)0.8-3.3.
  • Moel Hiraddug Mine, Dyserth, Clwyd: soft, black nodules of cobaltian asbolane were mined here from a fault-zone cutting Carboniferous Limestone, associated with red clay and hematite. The nodules were botryoidal or reniform but were small, only reaching a few cm in size (Le Neve Foster, 1882).
References:
  • Foster, C. Le Neve, 1882 On the occurrence of cobalt ores in Flintshire.  Transactions of the Royal Geological Society of Cornwall, 10, 107-112.
  • Roberts, D., 1986 Geochemistry of recent freshwater manganese tunnel deposits.  Unpublished Ph.D. thesis, University of Wales