Crystal System: Hexagonal
Status of Occurrence: Confirmed Occurrence
Chemical Composition: Calcium phosphate fluoride
Chemical Formula: Ca5(PO4)3F
Method(s) of Verification: Tyllau Mwyn - wet chemistry (Matthews & Scoon, 1964); Pen Caer - EMPA (R. Metcalfe, unpublished data).
- Hydrothermal: alpine type veins
Introduction: fluorapatite occurs in a wide variety of associations. In particular it is a minor phase in igneous rocks, especially those of alkaline affinity, as well as occurring as a component of ore deposits, particularly high-temperature tin-tungsten (Sn-W) associations. It is frequently observed in Alpine Fissure-type mineral assemblages. As it is often visually indistinguishable from other apatite-group minerals, confirmation requires analytical work.
Occurrence in Wales: analyses, required for full characterization, of apatite-group minerals from Wales are generally lacking and hence many occurrences are simply listed under apatite pending better data. Three occurrences of fluorapatite have been verified, two from Alpine Fissure-type veins and one from an igneous association.
- Pen Caer, Fishguard, Pembrokeshire: present in altered gabbros (R. Metcalfe, unpublished data).
- Prenteg, Tremadog, Gwynedd: Starkey & Robinson (1992) reported that apatite in the Alpine Fissure-type assemblage at this locality is fluorapatite. It forms colourless complex, sphere-shaped crystals to 1.5 mm associated with rutile, chamosite and albite.
- Tyllau Mwyn, Drws-y-nant, Gwynedd: recorded by Matthews & Scoon (1964) in stilpnomelane-bearing calcite veins. Compositionally this occurrence is close to ideal fluorapatite. Crystals vary in size from 'almost 1/2 in. in diameter down to less than 1 mm'.
- Matthews, D.W. & Scoon, J.H., 1964. Notes on a new occurrence of stilpnomelane from North Wales. Mineralogical Magazine, 33, 1032-1037.
- Starkey, R.E. & Robinson, G.W., 1992. Famous mineral localities, Prenteg, Tremadog, Gwynedd, Wales. Mineralogical Record, 23, 391-399.