Asbolane

Crystal System: Hexagonal
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Cobalt nickel manganese oxide hydroxide hydrate
Chemical Formula: (Co,Ni)1-y(MnO2)2-x(OH)2-2y+2x.nH2O
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).

There are no key localities for this specimen.

References:

  1. Foster, C. Le Neve, 1882. On the occurrence of cobalt ores in Flintshire. Transactions of the Royal Geological Society of Cornwall, 10, 107-112.
  2. Roberts, D., 1986. Geochemistry of recent freshwater manganese tunnel deposits. Unpublished Ph.D. thesis, University of Wales

There are no references for this specimen.