Diaspore

Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Aluminium oxide hydroxide
Chemical Formula: ά-AlO(OH)
Method(s) of Verification: Ludchurch - optical microscopy.

Chemical Group:

  • Oxides & Hydroxides

Geological Context:

  • Sedimentary: allogenic (detrital)
Introduction: diaspore is typically a white pearly mineral which is dimorphous with böhmite. It is a common component of bauxite (aluminium ore) and is found with corundum (Al2O3) in emery deposits. It is also know to form by low-grade metamorphism of tropically weathered silicates and as a hydrothermal alteration product of aluminous minerals such as sillimanite, andalusite, kyanite, pyrophyllite and corundum.
Occurrence in Wales: diaspore does not occur as a primary mineral in Wales, but is found as a detrital mineral within glacial deposits. Although described from just one locality, it is likely that it is more widely distributed within this deposit at least locally in Pembrokeshire.

Key Localities:

  • Ludchurch, Pembrokeshire: Griffiths & Stuart (1940) described the presence of diaspore, along with other detrital minerals, in sandy boulder clay at Ludchurch. The assemblage of detrital minerals, identified by these workers, was considered to be typical of the Irish Sea Drift of this area. The diapsore forms colourless plates up to 0.4 mm across.

References:

  1. Griffiths, J.C. & Stuart, A., 1940. An occurrence of detrital diaspore in South Wales. Geological Magazine, 77, 74-76.