Hedenbergite

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Calcium iron silicate
Chemical Formula: CaFe2+Si2O6
Method(s) of Verification: NE Anglesey - electron microprobe (Horák, 1993).

Chemical Group:

  • Silicates

Geological Context:

  • Metamorphic
  • Igneous
Introduction: hedenbergite is part of the pyroxene family and forms two series, one with diopside (CaMgSi2O6), and another with johannsenite (CaMnSi2O6). Hedenbergite is a rock-forming mineral which is found in fractionated tholeiitic igneous rocks, although it may also occur in acid igneous rocks; metamorphosed iron-rich rocks and limestone skarns.
Occurrence in Wales: as for many other silicate minerals, the presence of hedenbergite from Wales is poorly documented in the literature. A single occurrence of this mineral is known from the Precambrian calc-silicate rocks of NE Anglesey.

Key Localities:

  • North East Anglesey: Greenly (1919) reported the presence of clinopyroxene in Precambrian calc-silicate rocks of the Nebo Inlier (previously referred to as the Mona Complex); part of the Coedana Complex (Horák, 1993). He described two lithologies; forsterite marbles and crystalline limestone; but more detailed investigation has shown there to be three different pyroxene-bearing lithologies. Of these the calc-silicate marble and clinopyroxene-feldspar gneiss contain pyroxene compositions which span the diopside-hedenbergite boundary (Horák, 1993). In the clinopyroxene-feldspar gneiss the hedenbergite is associated with feldspar (microcline and plagioclase) and titanite, whereas in the calc-silicate marble quartz, plagioclase, minor titanite and garnet are present.

References:

  1. Greenly, E., 1919. The Geology of Anglesey. Memoirs of the Geological Survey of Great Britain, 980pp (2 volumes).
  2. Horák, J.M., 1993. The Late Precambrian Coedana and Sarn Complexes, Northwest Wales - a Geochemical and Petrological study. Unpublished Ph.D. thesis, University of Wales, 415pp.