Lepidolite

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Uncommon
Chemical Composition: Potassium lithium aluminium silicate fluoride hydroxide
Chemical Formula: K(Li,Al)3(Si,Al)4O10(F,OH)
Method(s) of Verification: all occurrences identified by polarizing microscope.

Chemical Group:

  • Silicates

Geological Context:

  • Sedimentary: allogenic (detrital)
  • Igneous
Introduction: lepidolite is a lithium-rich mica, belonging to the mica family. It is a pale mauve pink colour and is typically found in volatile-rich granites and granite pegmatites.
Occurrence in Wales: there are no recorded primary occurrences of lepidolite in Wales as volatile-rich and pegmatitic rocks are not characteristic of the granitic rocks in the Principality. The only reference to lepidolite is made by Griffiths (1939) who described pale blue to pink pleochroic crystals, forming a component of glacial deposits exposed in the area between the River Neath and the River Tywi in South Wales. These tills must therefore contain source debris derived from outside Wales, or were re-working older deposits eroded from such a source.

Key Localities:

There are no key localities for this specimen.

References:

  1. Griffiths, J.C., 1939. The mineralogy of the glacial deposits of the region between the Rivers Neath and Towy, South Wales. Proceedings of the Geologists’ Association, 50, 433-462.