Linarite

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Uncommon
Chemical Composition: Lead copper sulphate hydroxide
Chemical Formula: PbCu(SO4)(OH)2
Method(s) of Verification: Esgair Hir Mine - XRD (Rust & Mason, 1988); Frongoch Mine - EMPA (Green et al., 1996); Llechweddhelyg Mine - XRD & EMPA (Rust, 1990); Machen Quarry - XRD (NMW X-805 & X-909), IR & EPMA (Plant & Jones, 1995); Penrhiw Mine - XRD (Manchester Museum).

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
  • Supergene: in situ natural oxidation & weathering deposits
Sprays of linarite crystals, up to 3 mm across, from Esgairhir Mine. Specimen S.A. Rust Collection (721). Photo M.P. Cooper, © National Museum of Wales.
Linarite spray (4.5 mm across) from Nantmelin Mine. Specimen J.S. Mason Collection (JMNM 002). Photo D.I. Green, © National Museum of Wales.
Radiating spray of bladed linarite crystals from Eaglebrook Mine in the Central Wales Orefield. Specimen and photo S.A. Rust. © S.A. Rust.
Introduction: linarite is a beautiful mid to deep blue secondary sulphate mineral, popular amongst collectors both because of its colour and the perfection of crystals. These typically develop in radiating sprays of bladed crystals. Linarite forms in secondary environments, particularly in the oxidized zone of lead- and copper-bearing ore bodies and within weathered mine dumps.
Occurrence in Wales: Jones & Moreton (1977) provided the first record of linarite from Wales, listing a handful of localities in the Central Wales Orefield. Linarite has since been shown (Bevins, 1994), to be widespread in the Central Wales Orefield, typically forming through post-mining oxidation of dump material derived from lead-zinc-copper mines. A small number of in-situ discoveries have been made, but the best Welsh examples have undoubtedly formed through the alteration of primary chalcopyrite- and galena-bearing veinstone in mine tips. Crystals are never large (generally < 4 mm long), but this is offset by their beauty.

Key Localities:

  • Cwmystwyth Mine, Cwmystwyth, Ceredigion: fine individual lustrous blue microcrystals, crystal sprays and microcrystalline coatings have been collected from a stope within the Copper Level.
  • Dolwen Mine, Devil’s Bridge, Ceredigion: linarite forms a minor part of the secondary copper assemblage at Dolwen. Euhedral bladed microcrystals occur in cavities within altered chalcopyrite-bearing veinstone in a small section of dumps north of the Nant Rhuddnant. Linarite is typically associated with microcrystalline brochantite.
  • Dylife Mine, Penegoes, Powys: linarite occurs commonly, in weathered vein material in mine dumps following the lode outcrop from Dylife Shaft towards Dyfngwm Mine. Rust & Rust (1987) noted the potential for good microcrystals at Dyfngwm Mine (later corrected to outcrop workings at Dylife Mine) having observed crystalline crusts on rock and veinstone collected within a mine dump immediately south of opencut workings on Pen Dylife. Occasional euhedral bladed crystals (up to 1.2 mm) are reported with other crystal habits also present.
  • Eaglebrook (Nantycagl) Mine, Ceulanymaesmawr, Ceredigion: widely regarded as the classic Welsh linarite locality. Beautiful blue blades of linarite to 2 mm in length, commonly in radiating bunches were described by Braithwaite (1982). The presence of linarite within one small area of the dump suggests post-mining formation. Excellent microcrystals are recorded from cavities in a variety of matrixes including limonite, galena, quartz, and carbonates with other secondary minerals such as cerussite, malachite, brochantite, and anglesite being the most commonly occurring (Jones, 1983). Linarite is often observed coating acicular jackstraw cerussite, indicating a later stage of formation.
  • Esgairhir Mine, Tal-y-bont, Ceredigion: moderately common in altered veinstone from the mine dumps. Some fine examples displaying rich blue freestanding bladed prismatic crystals in sprays to 3 mm across have been recovered (Rust & Mason, 1988; Bevins, 1994). At Esgairhir, linarite is typically associated with malachite or brochantite.
  • Frongoch Mine, Devil's Bridge, Ceredigion: originally recorded by Jones & Moreton (1977) in a list of linarite localities from Mid-Wales. Occasional fine specimens of bladed linarite have been found, forming sprays (up to 2 mm across) associated with bindheimite-rich cavities in quartz veinstuff on the extensive dumps. Further examples have been recorded (Green et al., 1996) in association with brochantite and cerussite. A number of linarite-like specimens are reported by Green et al. (1996) to contain substantial selenium, although no fully quantitative analyses were performed. Tiny mid-blue spherules associated with linarite are possibly schmiederite, the selenatian analogue of linarite, but require verification.
  • Henfwlch Mine, Ceulanymaesmawr, Ceredigion: gemmy linarite crystal sprays (up to 2 mm) occur, in-situ within 'gossan' exposed in the adit level. Dump-formed linarite from Henfwlch is generally poorly formed, typically forming blue microcrystalline stains.
  • Llangynog Mine, Llangynog, Powys: attractive crystal sprays up to 1.5 mm across have been collected by S.A. Rust.
  • Llechweddhelyg Mine, Penrhyncoch, Ceredigion: rich aggregates of bright-blue microcrystals associated with cerussite occur but are rare. A second habit - minute bright blue spherules (up to 1 mm) on quartz - has been shown to have a composition midway in the series linarite-schmiederite, although slightly on the selenatian side of a 50:50 composition (Rust, 1990).
  • Machen Quarry, Caerphilly, South Wales: linarite is very rare at this locality, but occurs as minute, bright-blue, crystalline specks in typical barite matrix associated with lead-copper veining. It also forms transparent, blue, bladed crystals rarely more than 1 mm in length also found within galena-barite matrix (Plant & Jones, 1995).
  • Nantmelin Mine, Central Wales: superb, highly lustrous, intense blue, sharp bladed crystals and crystal sprays associated with fine gemmy anglesite microcrystals were collected from the small mine dumps in 1994. Specimens collected probably represent the best examples of the species in Central Wales (Bevins & Mason, 1997).
  • Penrhiw Mine, Ystumtuen, Ceredigion: some of the largest crystals from Wales have been collected from Penrhiw Mine. Matt blue crystals exceptionally to 4 mm occur on fractures in mudstone (Mason & Green, 1995).

References:

  1. Bevins, R.E., 1994. A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
  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. Braithwaite, R.S.W., 1982a. Wroewolfeite in Britain. Mineralogical Record, 13, 167-174.
  4. Green, D.I., Rust, S.A. & Mason, J.S., 1996. Classic British mineral localities: Frongoch Mine, Dyfed. UK Journal of Mines & Minerals, 17, 29-38.
  5. Jones, A.D., 1983. Nant-y-Cagl. Mineral Realm, 3, 42-76.
  6. Jones, J.A. & Moreton, N.J.M., 1977. The Mines and Minerals of Mid-Wales 40pp.
  7. Mason, J.S. & Green, D.I., 1995. Supergene minerals including exceptional ramsbeckite from Penrhiw Mine, Ystumtuen, Dyfed. UK Journal of Mines & Minerals, 15, 21-27.
  8. Plant, S.P. & Jones, I.E., 1995. Minerals of Machen Quarry, Mid Glamorgan, Wales. Journal of the Russell Society, 6(1), 31-36.
  9. Rust, S., 1985. British Micro Localities. No. 12: Esgair Hir Mine (SN 734913), Ceulanymaesmawr, Dyfed, Wales British Micromount Society Newsletter. 13. 13-14.
  10. Rust, S. & Rust, D., 1987. Micro-minerals from Dyfngwm Mine. U.K. Journal of Mines and Minerals, No. 2, 28-32.
  11. Rust, S.A., 1990b. Susannite and sulphatian schmeiderite from Llechwedd Helyg Mine, Tir-y-Mynach, Dyfed, Wales. U.K. Journal of Mines and Minerals, 8, 48
  12. Rust, S.A. & Mason, J.S., 1988. The minerals of Esgair-Hir mine, Dyfed, Wales. UK Journal of Mines & Minerals, 5, 35-43.