Devilline

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Calcium copper sulphate hydroxide hydrate
Chemical Formula: CaCu4(SO4)2(OH)6.3H2O
Method(s) of Verification: Bontddu - XRD (Natural History Museum, 6255F); Dolyhir Quarry - XRD and EDS (National Museum of Wales); Dylife Mine - visual identification; Eaglebrook (Nantycagl) Mine - XRD (Natural History Museum, x13804, x15539 & x15540).

Chemical Group:

  • Sulphates

Geological Context:

  • Supergene: in situ natural oxidation & weathering deposits
  • Supergene: post-mining oxidation & weathering deposits
Pale blue, wispy, devilline crystal sprays from a trial level near Bontddu, Dolgellau. Specimen and photo S.A. Rust. © S.A. Rust.
A spray (up to 0.75 mm across) of radiating, acicular devilline crystals from a trial level near Bontddu, Gwynedd. S.A. Rust Collection (no. 331). Photo M.P. Cooper, © National Museum of Wales.
Introduction: a secondary mineral typically found within oxidized copper-bearing veinstone. Devilline is visually very similar to serpierite and aurichalcite which, has caused confusion in the past. Particularly as all three minerals occur in similar geological environments.
Occurrence in Wales: devilline is the least common of the three species mentioned above, in Wales. Jones & Moreton (1977) provided the first account of devilline from Wales, describing very rare, blue-green interlaced crusts within gossan at Eaglebrook Mine in Central Wales. Devilline had, in fact, been discovered at Eaglebrook by R.S.W. Braithwaite during the 1960s, but was not published until the early 1980s (Braithwaite, 1982). Two other reported occurrences from the Central Wales Orefield made, during the 1980s remain unconfirmed. Further north, devilline was discovered by Saich & Rust (1987) in a short trial level near Bontddu in the Dolgellau Gold-belt and in the Welsh Borderlands devilline has been identified at Dolyhir Quarry (Cotterell et al., 2011). Without access to analytical equipment most new finds are labelled as serpierite which, appears to form more commonly than devilline in Wales. Unless primary zinc minerals are entirely absent, confident identification of devilline is not possible and even then analysis is recommended.

Key Localities:

  • Bontddu, Dolgellau, Gwynedd: material found, near Bontddu by Saich & Rust (1987), in a variety of habits on level walls in an old trial level north-west of Bontddu was shown by the Natural History Museum to be near the devilline end of the devilline-serpierite series. The mineral forms thin, blue-green lath-like, divergent crystals; tufted crystals on joints in veinstone; and as lattice-like crystal crusts.
  • Dolyhir Quarry, Old Radnor, Powys: although rare, devilline occurs as wispy, feathery, pearly, pale blue crusts associated with malachite coating altered massive copper sulphides from an exposure of Dolyhir Limestone in the north-west corner of the quarry (Cotterell et al., 2011).
  • Dylife Mine, Penegoes, Powys: pale, turquoise-blue, pearly, wispy aggregates associated with brochantite and linarite within weathered chalcopyrite and galena-bearing quartz veinstone is labelled as devilline on National Museum of Wales specimen NMW 68.576.GR.30. This was collected by R.S.W. Braithwaite during the 1960s and has not been analysed, so could well prove to be serpierite, a species well-known from the large dumps opposite the Star Inn at Dylife. Rust and Rust (1987) described a green crystalline botryoidal mineral from dumps on Pen Dylife as ‘devilline’. The crystal aggregates which, reach 1.5 mm across and consist of tightly packed thin hexagonal crystals is actually more likely to be schulenbergite.
  • Eaglebrook (Nantycagl) Mine, Ceulanymaesmawr, Ceredigion: the first and finest Welsh locality for devilline. R.S.W. Braithwaite discovered devilline at Eaglebrook in the 1960s (National Museum of Wales specimen NMW 68.576.GR.19) occurring as flat lying turquoise-blue to blue-green radial sprays on fracture surfaces in ferroan dolomite. The first written account of devilline from Eaglebrook was made by Jones & Moreton (1977) in describing very rare blue-green interlaced crusts in gossan while Braithwaite (1982) describes devilline as green blades to about 2 mm, typically coating fracture surfaces in massive dolomite. Both serpierite and aurichalcite also occur at Eaglebrook, but typically in subtly different settings. Devilline is restricted to fractures within weathered dolomite, forming light blue-green laths and crusts often highly striated occasionally forming small radiating aggregates (Jones, 1983).
  • Esgairhir Mine, Tal-y-bont, Ceredigion: Rust (1985) tentatively identified devilline from Esgair Hir Mine, typically forming light green to lime green feathery and lath-like microcrystals, occasionally aggregated into divergent masses. Subsequently Rust & Mason (1988) make no mention of devilline, suggesting that this was a misidentification, probably of the newly described species redgillite.

There are no key localities for this specimen.

References:

  1. Braithwaite, R.S.W., 1982a. Wroewolfeite in Britain. Mineralogical Record, 13, 167-174.
  2. 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.
  3. Dunn, P.J. & Rouse, R.C., 1975. Wroewolfeite, a new copper sulphate hydroxide hydrate. Mineralogical Magazine, 40, 1-5.
  4. Jones, A.D., 1983. Nant-y-Cagl. Mineral Realm, 3, 42-76.
  5. Jones, J.A. & Moreton, N.J.M., 1977. The Mines and Minerals of Mid-Wales 40pp.
  6. Rust, S., 1985. British Micro Localities. No. 12: Esgair Hir Mine (SN 734913), Ceulanymaesmawr, Dyfed, Wales British Micromount Society Newsletter. 13. 13-14.
  7. Rust, S. & Rust, D., 1987. Micro-minerals from Dyfngwm Mine. U.K. Journal of Mines and Minerals, No. 2, 28-32.
  8. Rust, S.A. & Mason, J.S., 1988. The minerals of Esgair-Hir mine, Dyfed, Wales. UK Journal of Mines & Minerals, 5, 35-43.
  9. 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.

There are no references for this specimen.