Lepidocrocite

Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Iron oxide hydroxide
Chemical Formula: γ-Fe3+O(OH)
Method(s) of Verification: unknown.

Chemical Group:

  • Oxides & Hydroxides

Geological Context:

  • Supergene: in situ natural oxidation & weathering deposits
Introduction: lepidocrocite is a secondary mineral, polymorphous with akaganeite, feroxyhyte, and goethite, which result from the oxidation of primary iron-bearing minerals in soils and mineral deposits. Lepidocrocite is particularly important as a component of gleyed soils.
Occurrence in Wales: records of lepidocrocite from Wales are few, although it is probably much more common. Those that do exist relate to its presence in soils distributed in Mid and North-Wales (Brown, 1953; Adams & Kassim, 1984), while traces of crystalline lepidocrocite may be present in the goethitic iron ore at Llanharry Mine in South Wales (Bevins & Mason, 2000).

Key Localities:

  • Anglesey: identified in certain soils by Brown (1953).
  • Central Wales: abundant and widespread in the soils of Mid-Wales, in particular in brown earths of the Denbigh Soil Series (Adams & Kassim, 1984).
  • Llanharry Iron Mine, Llantrisant, South Wales: lepidocrocite is listed as a primary mineral by Bevins & Mason (2000) without further details. Lepidocrocite is typically a secondary mineral. At Llanharry some specimens of stalactitic goethite are coated with tiny platy red crystals which are possibly secondary lepidocrocite (T.F. Cotterell, unpublished data). Further analysis is required to confirm this occurrence.

References:

  1. Adams, W.A., & Kassim, J.K., 1984. Iron oxyhydroxides in soils developed from Lower Palaeozoic sedimentary rocks in mid-Wales and implications for some pedogenetic processes. Journal of Soil Science, 35, 117-126.
  2. Bevins, R.E. & Mason, J.S., 2000. Welsh Metallophyte and metallogenic evaluation project: Results of a Minesite Survey of Glamorgan and Gwent. National Museums & Galleries of Wales, Cardiff
  3. Brown, G., 1953. The occurrence of lepidocrocite in some British soils. Journal of Soil Science, 4, 220-228.