Collophane

Crystal System: Amorphous
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Locally Abundant
Chemical Composition: Calcium phosphate fluor-chlor-hydroxide
Chemical Formula: Ca5(PO4)3(F,OH,Cl)
Method(s) of Verification:

Chemical Group:

  • Phosphates

Geological Context:

  • Hydrothermal
  • Sedimentary: diagenetic
Introduction: collophane is fine-grained and non-crystalline, variety of apatite, most commonly carbonate-fluorapatite or carbonate-hydroxylapatite. The term collophane is not an IMA approved mineral name.
Occurrence in Wales: Woodward (1939b) described the presence of cryptocrystalline collophane intergrown with chlorite and associated with calcite in dark greenish-black, vitreous nodules set in a lighter matrix, at Benallt Manganese Mine near, Rhiw, Llŷn. This represented the first description of collophane from the British Isles. Groves (in Campbell Smith et al., 1944b) noted that a small amount of collophane is present in virtually all manganese ores from this locality, and reported that the largest and palest nodules in the No.1 ore-body consist entirely of collophane. Collophane is also recorded as being a minor component in the manganese ores of Cambrian age exposed in the Harlech Dome region of southern Snowdonia, forming nodules up to 0.5 mm in diameter in the Gamalan Flags (de Béthune, 1972). Trythall (1988) noted that phosphate in nodules of the Ordovician ironstones exposed across North Wales is commonly considered to be collophane, although X-ray diffraction of this material shows that it is carbonate-hydroxylapatite.

Key Localities:

There are no key localities for this specimen.

References:

  1. Béthune S. de, 1972. Etude á la microsonde électronique des minéraux métamorphiques du Cambrien de Harlech (Pays de Galles). Bulletin de la Société Belge de Géologie de Paléontologie et d'Hydrologie, 81, 255-265.
  2. Campbell Smith, W., Bannister, F.A. & Hey, M.H., 1944b. Banalsite, a new barium-feldspar from Wales. Mineralogical Magazine 27, 33-47
  3. Trythall, R.J.B., 1988. The Mid-Ordovician Oolitic Ironstones of North Wales. Unpublished D.Phil. thesis, Luton College of Higher Education.
  4. Woodland, A.W., 1939b. The petrography and petrology of the Lower Cambrian manganese ores of western Merionethshire. Proceedings of the Geologists' Association, 50, 205-222.