Mineral Database

Mineral Database
Mineralogy of Wales

Titanite

Crystal System: Monoclinic
Formula: CaTiSiO5
Status of Occurrence: Confirmed Occurrence
Distribution: Widespread
Chemical Composition: Calcium titanium silicate
Method(s) of Verification: all localities cited except Fron Oleu - polarizing microscope; Anglesey - EMPA (Horák, 1993)

Scanning electron micrograph image of a detached titanite crystal from Benallt Mine. Image T.F. Cotterell, © National Museum of Wales.

Chemical Group:
  • Silicates
Geological Context:
  • Hydrothermal : alpine type veins
  • Metamorphic
  • Igneous
Introduction: titanite, the International Mineralogical Association (IMA) approved name for the mineral also known as sphene, is found as an accessory mineral in acidic igneous rocks, it also develops in contact and low-grade regional metamorphic rocks and is a common alteration product of ilmenite.
Occurrence in Wales: titanite is widely distributed across Wales as a low-grade metamorphic mineral in rocks of basaltic composition. It typically forms anhedral dusty granules up to 0.1 mmacross associated with chlorite in the groundmass of the rocks, or pseudomorphing primary titanium-oxides. Electron microprobe analyse show a characteristic substitution of aluminium and iron for titanium, as reported elsewhere in titanite occurring in low-grade metamorphic rocks (Bevins & Rowbotham, 1983; Bevins,& Merriman, 1988).
Key Localities:
  • Anglesey: titanite also occurs as a secondary phase within basic gneisses (amphibolites), in central Anglesey, forming large rhombic crystals and less distinct crystal aggregates after ilmenite (Horák, 1993).
  • Prenteg, Tremadog, Gwynedd: at Fron Oleu Starkey & Robinson (1992) recorded titanite in alpine-type veins generated by hydrothermal activity.
  • Snowdonia, Gwynedd: titanite is present as an accessory phase in various rhyolitic rocks in Snowdonia, Gwynedd (Campbell et al., 1987; Howells et al., 1991) where it forms euhedral crystals up to 200 μm across, with some crystals showing well-developed sector zoining, with tin-rich cores with up to 3.5 wt% SnO2 (A.T. Kearsley, unpublished data, quoted in Bevins, 1994).
References:
  • Bevins, R.E. & Rowbotham, G., 1983 Low-grade metamorphism within the Welsh sector of the paratectonic Caledonides.  Geological Journal, 18, 141-167
  • Bevins,R.E. & Merriman, R. J., 1988 Compositional controls on co-existing prehnite-actinolite and prehnite-pumpellyite assemblages in the Tal y Fan metabasite intrusion, North Wales: implications for Caledonian metamorphism field gradients.  Journal of Metamorphic Geology, 6, 17-39.
  • Campbell, S.D.G., Reedman, A.J., Howells, M.F. & Mann, A.C., 1987 The emplacement of geochemically distinct groups of rhyolities during the evolution of the Lower Rhyolitic Tuff Formation caldera (Ordovician), North Wales, U.K.  Geological Magazine, 124, 501-511.
  • 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.
  • Howells, M.F., Reedman, A.J. & Campbell, S.D.G., 1991 Ordovician (Caradoc) marginal basin volcanism in Snowdonia (north-west Wales).  HMSO for the British Geological Survey, 191pp.
  • Starkey, R.E. & Robinson, G.W., 1992 Famous mineral localities, Prenteg, Tremadog, Gwynedd, Wales.  Mineralogical Record, 23, 391-399.