Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Chemical Composition: Calcium copper arsenate carbonate hydroxide hydrate
Chemical Formula: CaCu5(AsO4)2(CO3)(OH)4.6H2O
Method(s) of Verification: Capel Hermon - XRD (National Museum of Wales); Gwaith-yr-afon Mine - IR (Rust & Mason, 1994).
- Supergene: in situ natural oxidation & weathering deposits
Radial tyrolite sprays (to 2 mm across) with azurite in limestone from Dolyhir Quarry. Specimen and photo D.I. Green. © D.I. Green.
Tyrolite-like mineral forming flat-lying, radiating aggregates coating microtonalite. Capel Hermon. Specimen J.S. Mason Collection, photo D.I. Green; © National Museum of Wales.
Radiating tyrolite sprays (to 2 mm in diameter) from Gwaith-yr-Afon Mine, Central Wales Orefield. Photo J.S. Mason, © National Museum of Wales.
Introduction: Tyrolite is a copper-arsenic mineral found in supergene assemblages including post-mining environments.
Occurrence in Wales: tyrolite is a rare mineral in the British Isles. Wales has produced some of the more notable occurrences, particularly over recent years. Saich & Rust (1987) describe a 'tyrolite'-like mineral from a trial level near Bontddu, Dolgellau, Gwynedd. Although still unconfirmed, further discoveries have resulted in some of the best British tyrolite being collected. Fine radiating sprays of a sulphatian tyrolite, coating fracture surfaces in veinstone at Gwaith-yr-afon Mine in Central Wales were collected in the late 1980s (Rust & Mason, 1994) and more recently superb specimens of platy tyrolite rosettes have been found at Dolyhir Quarry in Powys (Cotterell et al., 2011).
- Bontddu, Dolgellau, Gwynedd: Saich & Rust (1987) report a 'tyrolite'-like mineral, typically forming exceedingly rare bright blue scattered flattened radial sprays and hemispherical masses to 0.2 mm, and as botryoidal masses on joints in veinstone from a trial level near Bontddu. Bevins (1994) describes the botryoidal masses as reaching 2 mm across.
- Capel Hermon, Coed y Brenin, Gwynedd: Armstrong et al. (2003) describe tyrolite and malachite altering from small patches of tennantite within intensely sericitised microtonalite from a forest road-cut at NGR SH 748 256. Analysis of material collected by the National Museum of Wales shows this mineral to have an X-ray diffraction pattern similar to tyrolite, although not identical. This tyrolite-type mineral forms flat-lying radiating aggregates (to several mm across) of platy pearly bluish green crystals coating the microtonalite in association with tennantite.
- Dolyhir Quarry, Old Radnor, Powys: superb crystallized samples to large hand specimen size collected, from a chalcocite vein exposed in Dolyhir Limestone at the northern end of the quarry, display rich, pearly, bluish green tyrolite in radial sprays to 8 mm across and dark blue azurite. Tyrolite has also been found as radiating sprays on fracture planes within gritty sandstone near to the quarry entrance.
- Gwaith-yr-Afon Mine, Goginan, Ceredigion: described by Rust & Mason (1994) as low carbonate, sulphatian tyrolite. Tyrolite, occurs abundantly underground as bright blue, green or whitish flat-lying radial groups of sectile lath-like crystals in fractures in altered quartz-chalcopyrite veinstone. Occasional spherical aggregates of compact platy crystals occur within quartz cavities. Crystal sprays reach 4 mm in diameter, but are typically 1-2 m across. A number of fine small display specimens richly covered with radiating sprays have been collected. In comparison with other arsenate minerals tyrolite is locally very abundant at Gwaith-yr-Afon.
- Armstrong, R., Herrington, R.J. & Savage, M.A., 2003. Tennantite and tyrolite from the Coed y Brenin forest, North Wales. Journal of the Russell Society, 8(1), 18.
- Bevins, R.E., 1994. A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
- 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.
- Cotterell, T.F., Green, D.I., Hubbard, N., Mason, J.S., Starkey, R.E. and Tindle, A.G., 2011. The Mineralogy of Dolyhir Quarry, Old Radnor, Powys, Wales. UK Journal of Mines and Minerals, 32, 5-61.
- Rust, S.A. & Mason, J.S., 1994. An unusual occurrence of arsenate minerals at Gwaith-yr-Afon mine, Dyfed, Wales. Journal of the Russell Society, 5(2), 109-113.
- Saich, D.A. & Rust, S.A., 1987. Micro-minerals from a trial level in Wales. U.K. Journal of Mines and Minerals, No. 3, 3-4.