Carbonate-fluorapatite

Crystal System: Hexagonal
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Calcium phosphate carbonate fluor hydroxide
Chemical Formula: Ca5(PO4,CO3)3(F,OH,O)
Method(s) of Verification: North Wales - XRD (Trythall, 1988); Aberpergwm Colliery - XRD at the Natural History Museum (X-ray reference no. 11969 in Plant & Evans, 2005); Gelli Colliery - IR (Plant & Evans, 2005).

Chemical Group:

  • Phosphates

Geological Context:

  • Sedimentary: diagenetic
Scanning electron micrograph of hexagonal 'flying-saucer'-shaped carbonate-fluorapatite crystals from Parc Slip West opencast coal mine, near Bridgend, South Wales. © National Museum of Wales.
Introduction: also known as francolite, carbonate-fluorapatite is found in phosphatic rocks and some ironstones.
Occurrence in Wales: Trythall (1988) published X-ray diffraction data to show that nodules from Ordovician ironstones exposed across North Wales, were composed of carbonate-fluorapatite and not collophane (amorphous apatite). More recently well-crystallized carbonate-fluorapatite has been discovered in clay ironstone nodules associated with the South Wales Coalfield (Plant & Evans, 2005).

Key Localities:

  • South Wales Coalfield: carbonate-fluorapatite forming small (typically <2 mm) hexagonal platy crystals has been recorded (Plant & Evans, 2005) from several collieries, including Aberpergwm, Abercynon, Cambrian, Gelli, Parc and Parc Slip West opencast. It is probably more widespread, but is easily overlooked because of its superficial resemblance to siderite (a common mineral within ironstone nodules).

References:

  1. Plant, S. & Evans, D., 2005. Carbonate-fluorapatite from the Westphalian coal measures of South Wales, U.K. Journal of the Russell Society, 8(2), 98-101.
  2. Trythall, R.J.B., 1988. The Mid-Ordovician Oolitic Ironstones of North Wales. Unpublished D.Phil. thesis, Luton College of Higher Education.