Mineral Database
Crystal System:
Formula:
Status of Occurrence:
Distribution:
Chemical Composition:
Method(s) of Verification:
Geological Context:
- Supergene : in situ natural oxidation & weathering deposits
Key Localities:
- Bwlchrhennaid Mine, Goginan, Ceredigion: feathery microcrystals coat pale grey mudstone from the dumps at this mine. Rare orange tabular wulfenite microcrystals form an attractive but, unusual asscociation (Mason, 1992).
- Coed Cefn Pwll-du, Draethen, South Wales: well-formed bladed crystals (up to 4 mm in length) line cavities within barite cutting dolomitic limestone from an outcrop containing an assemblage very similar in appearance to that from Machen Quarry.
- Craig Rhiwarth Mine, Llangynog, Powys: specimens collected by Warrington W. Smyth in 1846 were later described by Arthur Russell as containing hemimorphite (Williams, 1985). Specimen no. 694 in the British Micromount Society Reference collection is hemimorphite collected by M. Rothwell.
- Cwmleyshon Quarry, Draethen, South Wales: similar in appearance to material from Coed Cefn Pwll-du, at Cwmleyshon; cream coloured translucent crystals exceptionally reach 36 mm in length, although are typically only 1 or 2 mm long. Some of the largest crystals were collected in 1990 by Dr. F. Ince (e.g. specimen NMW 90.47G.M.1.).
- Cwmystwyth Mine, Cwmystwyth, Ceredigion: post-mining crusts composed of radiating spherical crystal aggregates (to 2.5 mm) coat tunnel walls underground within Level Fawr. This occurrence has been known about for some time. G. J. Williams, the former Mine Inspector for Wales had a specimen in his collection labelled as Devil’s Bridge, Cardiganshire. This specimen now in the National Museum of Wales colletcion (NMW 27.111.GR.335) is almost certainly from underground workings at Cwmystwyth Mine, where, from the late 1970’s onwards, collectors have continued to find good specimens.
- Dylife Mine, Penegoes, Powys: hemimorphite was formerly common at this locality, particularly from the large dumps opposite the Star Inn. During the late 1960’s, R. S. W. Braithwaite collected sugary opaque white botryoidal hemimorphite (e.g NMW 68.576.GR.16) while Jones and Moreton (1977) describe tufts of colourless transparent tabular crystals on sphalerite.
- Eaglebrook (Nantycagl) Mine, Ceulanymaesmawr, Ceredigion: creamy coloured hemimorphite veining siltstones occurs on the dumps of the Eastern Shaft. Porous masses to 60 x 40 mm have been found containing fine bladed crystals. Specimens in the National Museum of Wales collection, labelled Esgair Hir Mine, are believed to be derived from Esgair Fraith Mine – the eastward extension of the Esgair Hir Lode. Material collected by A. Dean in 1976 originally labelled smithsonite has, since been shown to be hemimorphite and this is also likely to be the case with the smithsonite reported by Jones and Moreton (1977). Crystals from Esgair Fraith are amongst the finest to have been collected in Mid-Wales.
- Esgair Fraith Mine, Tal-y-bont, Ceredigion: creamy coloured hemimorphite veining siltstones occurs on the dumps of the Eastern Shaft. Porous masses to 60 x 40 mm have been found containing fine bladed crystals. Specimens in the National Museum of Wales collection labelled Esgair Hir Mine are believed to be derived from Esgair Fraith Mine – the eastward extension of the Esgair Hir Lode. Material collected by A. Dean in 1976 originally labelled smithsonite has, since been shown to be hemimorphite and this is also likely to be the case with the smithsonite reported by Jones and Moreton (1977). Crystals from Esgair Fraith are amongst the finest to have been collected in Mid-Wales.
- Frongoch Mine, Devil's Bridge, Ceredigion: somewhat surprisingly, given the abundance of primary sphalerite, hemimorphite is rare at this locality. It characteristic forms drusy bladed crystals lining cavities to 2 cm x 1 cm and radiating crystal groups to 3 mm on goethite.
- Halkyn, Flintshire: small spherical crystal clusters scattered on calcite containing sphalerite inclusions are displayed on National Museum of Wales specimen NMW 68.378.GR.24.
- Hendy Quarry, Miskin, South Wales: listed by Dr. Stephen Plant in 1993 as part of the supergene zinc-copper assemblage (British Micromount Society Newsletter No. 35).
- Henfwlch Mine, Ceulanymaesmawr, Ceredigion: botryoidal crusts and occasional crystal clusters within ferroan dolomite have been collected from the adit level dumps. Recently fine specimens of colourless stepped crystals lining cavities in crumbly brown corroded ferroan dolomite have been collected underground.
- Holywell, Flintshire: listed without description by Neil (1907).
- Llangynog Mine, Llangynog, Powys: British Micromount Society Reference Collection specimen no. 680 is hemimorphite from this locality, collected by M. Rothwell.
- Lletty Evan-Hen Mine, Bont-goch, Ceredigion: hemimorphite occurs as attractive white to pale blue thick botryoidal crusts covering areas to 5 cm across and rarely radiating tabular crystals to 7 mm long.
- Machen Quarry, Caerphilly, South Wales: hemimorphite from this locality was described as relatively common by Plant & Jones (1995). Well-formed waterclear to honey-coloured, radiating, tabular crystals line cavities up to 5 cm across, in barite veins cutting dolomitic limestone. Crystals are usually less than 1 mm but, occasionally reach 4 mm. Hemimorphite was known from the late 1970’s, although the quality of early specimens does not compare with those found in recent years. The best examples show a high degree of lustre and represent the finest hemimorphite from Wales.
- Minera District, Flintshire: 3-5 mm brown sheaves on quartz and calcite are reported (J.S. Mason, unpublished data).
- Nant Mine, Llangunnor, Carmarthenshire: a solid greyish-white mass, in the National Museum of Wales collection, is labelled as hemimorphite but formal identification has not been made.
References:
- Classic British mineral localities: Frongoch Mine, Dyfed. UK Journal of Mines & Minerals, 17, 29-38.
- Nant-y-Cagl. Mineral Realm, 3, 42-76.
- The Mines and Minerals of Mid-Wales 40pp.
- British Minerals and where to find them. Murby’s Science Series. 224pp.
- Minerals of Machen Quarry, Mid Glamorgan, Wales. Journal of the Russell Society, 6(1), 31-36.
- Wulfenite in the British Isles. UK Journal of Mines & Minerals, 11, 30-41.
- British Mineralogy: or coloured figures intended to elucidate the mineralogy of Great Britain. Vol. V. London.
- The Old Mines of the Llangynog District. British Mining, No. 26. Northern Mine Research Society, 128pp.
