Chrysocolla

Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Copper aluminium silicate hydroxide hydrate
Chemical Formula: (Cu,Al)2H2Si2O5(OH)4.nH2O
Method(s) of Verification: Dinorwic Quarry - XRD (NMW X-819); Llechweddhelyg Mine - XRD (NMW X-825) & wet chem. analysis; Lletty Evan Hen Mine - XRD (NMW X-826); Mynyddgorddu Mine - XRD (NMW X-827); Gwaithyrafon Mine - IR spectrometry.

Chemical Group:

  • Silicates

Geological Context:

  • Supergene: in situ natural oxidation & weathering deposits
Turquoise-blue chrysocolla within quartz-siderite veins cutting metadolerite. Penrhyn Quarry. Specimen National Museum of Wales (NMW 98.16G.M.14), photo D.I. Green, © National Museum of Wales.
Massive chrysocolla forming turquoise-blue to green cement in altered chalcopyrite-bearing mudstone breccia. Mynyddgorddu Mine. Specimen National Museum of Wales (NMW 2003.1G.M.352b), photo D.I. Green, © National Museum of Wales.
Introduction: a secondary mineral which occurs in the oxidized zone of copper-bearing ore bodies.
Occurrence in Wales: chrysocolla is an attractive mineral, typically occurring as turquoise-blue to blue-green masses displaying no crystal form. The earliest known specimen of chrysocolla from Wales is, a sample collected at Dinorwic Quarry, Snowdonia in 1910. The specimen forms part of the G.J. Williams Mineral Collection housed in the National Museum of Wales (NMW 27.111.GR.447). Although uncommon in Wales, a small number of localities have provided good examples of this species, most notably Mynyddgorddu Mine in the Central Wales Orefield and, more recently, Penrhyn Slate Quarry near Bethesda in Snowdonia. The majority of occurrences are from the Central Wales Orefield where, chrysocolla forms a minor component of in-situ supergene copper assemblages, typically in association with highly altered chalcopyrite. Chrysocolla is a very distinctive mineral, in part due to its colour and massive form, allowing visual identification to be made where larger masses are found. Analytical confirmation has been made of material from a number of Welsh localities.

Key Localities:

  • Bontddu, Dolgellau, Gwynedd: thin crusts of chrysocolla occur on joints in veinstone and replacing malachite in a disused trial level near Bontddu. Very rarely chrysocolla forms superb translucent micro-stalactites from pale blue to greenish blue (Saich & Rust, 1987).
  • Dinorwic Quarry, Llanberis, Gwynedd: extensive alteration of chalcocite has, resulted in dark blue-green chrysocolla, as shown by National Museum of Wales specimen NMW 27.111.GR.447, formerly in the collection of G.J.Williams.
  • Dylife Mine, Penegoes, Powys: smooth botryoidal crusts are reported by Jones & Moreton (1977).
  • Esgair Fraith Mine, Tal-y-bont, Ceredigion: a sky blue earthy variety is noted from Esgairfraith (Jones & Moreton, 1977).
  • Esgairhir Mine, Tal-y-bont, Ceredigion: at Esgairhir blue-green crusts form the matrix on which other secondary minerals have crystallized (Rust & Mason, 1988).
  • Glogfawr Mine, Ysbyty Ystwyth, Ceredigion: bright turquoise-blue masses to 10 mm across have been collected from the mine dumps (T.F. Cotterell, unpublished data).
  • Gwaith-yr-Afon Mine, Goginan, Ceredigion: deep blue-green conchoidal masses displaying desiccation cracks occur commonly within intensely altered chalcopyrite-bearing veinstone in-situ within one of the adit levels. Some specimens display partial alteration of tyrolite to chrysocolla (Rust & Mason, 1994).
  • Llechweddhelyg Mine, Penrhyncoch, Ceredigion: rich examples, often displaying a somewhat powdery form and invariably associated with malachite, occur within copper-rich gossan (Jones, 1987) derived from the Eastern Engine Shaft.
  • Mynyddgorddu Mine, Bontgoch, Ceredigion: abundant chrysocolla occurs as massive, richly coloured turquoise-blue to green cement in altered chalcopyrite-bearing mudstone breccia (Bevins & Mason, 1997). A small number of fine display specimens have been found.
  • Penrhyn Quarry, Bethesda, Gwynedd: Bevins & Mason (1998) reported occasional fine specimens. Chrysocolla from Penrhyn is typically an intense turquoise-blue colour and occurs within quartz-siderite veins cutting metadolerite (National Museum of Wales specimen NMW 98.16G.M.14).
  • Sigenlas Mine, Llanidloes, Powys: chrysocolla is a minor constituent of highly altered chalcopyrite-rich veinstone at this locality.

There are no key localities for this specimen.

References:

  1. Bevins, R.E. & Mason, J.S., 1998. Welsh Metallophyte and metallogenic evaluation project: Results of a Minesite Survey of Gwynedd. National Museums of Wales, Cardiff.
  2. 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.
  3. Jones, A.D., 1987. The minerals of Llechweddhelyg. U.K. Journal of Mines and Minerals, No. 3, 25-27.
  4. Jones, J.A. & Moreton, N.J.M., 1977. The Mines and Minerals of Mid-Wales 40pp.
  5. 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.
  6. Rust, S.A. & Mason, J.S., 1988. The minerals of Esgair-Hir mine, Dyfed, Wales. UK Journal of Mines & Minerals, 5, 35-43.
  7. 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.