You are here:  >   >   >   >   >   > 
Cymraeg

Rutile

Crystal System: Tetragonal
Status of Occurrence: Confirmed Occurrence
Distribution: Widespread
Chemical Composition: Titanium dioxide
Chemical Formula: TiO2
Method(s) of Verification: all occurrences cited are based on confident visual identifications

Geological Context:

Prismatic rutile crystal in quartz from Clogau Mine. Field of view 15 mm across. J.S. Mason Collection (JM 2540). Photo D.I. Green, © National Museum of Wales.
Introduction: rutile is a frequently-observed accessory mineral in igneous (especially intrusive) rocks and as a detrital mineral in sedimentary rocks: it is often present in the metamorphosed equivalents of both. In mineral veins it is less frequent, except in those of the alpine fissure-type, where it is sometimes common, and is invariably associated with quartz, albite, chlorite, apatite, the other TiO2 polymorphs (anatase and brookite) and rare-earth minerals like synchysite. Rutile is readily identified when well-crystallized owing to its tendency to form dense aggregates of golden hairlike crystals, which when embedded in clear quartz, constitutes the semi-precious gemstone known as sagenite or rutilated quartz. Coarser crystals tend to be darker in colour but again the prismatic to acicular habit and the association is diagnostic.
Occurrence in Wales: early reports of rutile in Wales were limited to descriptions of its occurrence as a rock-forming mineral, as in its presence in the basaltic tuffs of the Bedded Pyroclastic Formation on Lliwedd in the Snowdon range (Williams, 1927). More recently, the attention given to alpine fissure-type veins by mineral collectors has resulted in many more discoveries, which are listed below with references. In igneous rocks, rutile often develops by the breakdown of primary iron-bearing minerals such as ilmenite, as described in dolerites from the Preseli hills of SW Wales by Ixer (in Thorpe et al., 1991) and at Parys Mountain on Anglesey (Pointon & Ixer, 1980). A common product of such a reaction is a mixture of quartz and rutile which is generally referred to as leucoxene.

Key Localities:

References:

  1. Bevins, R.E. & Mason, J.S., 1997. Welsh metallophyte and metallogenic evaluation project: Results of a minesite survey of Dyfed and Powys. CCW Contract Science Report No. 156. National Museums & Galleries of Wales.
  2. Green, D.I. & Middleton, D., 1996. Alpine-type vein minerals from Tanygrisiau, Gwynedd. U.K. U.K. Journal of Mines and Minerals, 16, 30-33.
  3. Mason, J.S., 1997. Regional polyphase and polymetallic vein mineralisation in the Caledonides of the Central Wales Orefield. Transactions of the Institution of Mining and Metallurgy (Section B: Applied Earth Science), 106, B135-B144.
  4. Naden, J., 1988. Gold mineralisation in the Caledonides of the British Isles with reference to the Dolgellau Gold Belt and the Southern Uplands of Scotland. Unpublished Ph.D thesis, University of Aston, UK.
  5. Pointon, C.R. & Ixer, R.A., 1980. Parys Mountain mineral deposit, Anglesey, Wales: geology and ore mineralogy. Transactions of the Institution of Mining and Metallurgy (Section B: Applied earth science), 89, B143-B155.
  6. Rust, S., 1993. Alpine minerals from the Bryn-yr-Afr Mine, Mid Wales. British Micromount Society Newsletter No. 35, 7
  7. Starkey, R.E. & Robinson, G.W., 1992. Famous mineral localities, Prenteg, Tremadog, Gwynedd, Wales. Mineralogical Record, 23, 391-399.
  8. Starkey, R.E., Hubbard, N. & Bayley, M.P., 1991. Mineralization at Hendre Quarry, Glyn Ceiriog, Clwyd, Wales. U.K. Journal of Mines and Minerals, No. 10, 48-51.
  9. Thorpe, R.S., Williams-Thorpe, O., Jenkins, D.G. & Watson, J.S., 1991. The geological sources and transport of the bluestones of Stonehenge, Wiltshire, U.K. Proceedings of the Prehistoric Society, 57, 103-157.
  10. Williams, H., 1927. The geology of Snowdon (North Wales). Quarterly Journal of the Geological Society of London, 83, 346-431.