Mineral Database (Saesneg yn unig)
Tyrolite
Crystal System: Orthorhombic
Formula: CaCu5(AsO4)2(CO3)(OH)4.6H2O
Status of Occurrence: Confirmed Occurrence
Distribution: Uncommon
Chemical Composition: Calcium copper arsenate carbonate hydroxide hydrate
Method(s) of Verification: Capel Hermon - XRD (National Museum of Wales); Gwaith-yr-afon Mine - IR (Rust & Mason, 1994).
Chemical Group:
- Arsenates
Geological Context:
- Supergene : in situ natural oxidation & weathering deposits
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).
Key Localities:
- 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.
References:
- Tennantite and tyrolite from the Coed y Brenin forest, North Wales. Journal of the Russell Society, 8(1), 18.
- A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
- 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.
- The Mineralogy of Dolyhir Quarry, Old Radnor, Powys, Wales. UK Journal of Mines and Minerals, 32, 5-61.
- An unusual occurrence of arsenate minerals at Gwaith-yr-Afon mine, Dyfed, Wales. Journal of the Russell Society, 5(2), 109-113.
- Micro-minerals from a trial level in Wales. U.K. Journal of Mines and Minerals, No. 3, 3-4.
