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.


  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 Unpublished Ph.D. thesis, University of Wales, 415pp.