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Hastingsite

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Sodium calcium iron magnesium aluminium silicate hydroxide
Chemical Formula: NaCa2(Fe2+,Mg)4Fe3+(Si6Al2)O22(OH,Cl)2
Method(s) of Verification: St David's Head - EMPA (Bevins, et al., 1994); Tan-y-Grisiau - polarizing microscope (Bromley, 1969).

Chemical Group:

  • Silicates

Geological Context:

  • Igneous
Introduction: hastingsite is an amphibole belonging to the calcic amphibole group. It occurs as a rock-forming mineral in basic igneous rocks.
Occurrence in Wales: as with many other ferro-magnesian minerals, hastingsite has only been confirmed from a few localities in Wales, although it is quite likely that it is more abundant than these reports reflect.

Key Localities:

There are no key localities for this specimen.

References:

  1. Bevins, R.E., Lees, G.J. Roach, R.A. Rowbotham, G. & Floyd, P.A., 1994. Petrogenesis of the St David’s Head Layered Intrusion, Wales: a complex history of multiple magma injection and in situ crystallisation. Transactions of the Royal Society of Edinburgh: Earth Sciences, 85, 91-121
  2. Bromley, A.V., 1969. Acid plutonic igneous activity in the Ordovician of North Wales. In: Wood, A. (ed.) The Pre-Cambrian and Lower Palaeozoic rocks of Wales. University of Wales Press, 387-408.
  3. Roach, R.A., 1969. The composite nature of the St. David's Head and Carn Llidi intrusions of North Pembrokeshire. In: Wood, A. (ed.) The Pre-Cambrian and Lower Palaeozoic rocks of Wales, University of Wales Press, Cardiff, 409-433.