Pyromorphite specimens from the British Isles

Pyromorphite from Ireland and Scotland

pyromorphite [332 kb] pyromorphite [390 kb]

Figs. 1-2: Left: Coarse, vuggy milky quartz, voids coated with orange limonite and lesser, granular, fine-grained, pale yellow pyromorphite. From the Old Luganure mine, Glendasan, county Wicklow, Ireland. The adjacent valleys of Glendalough and Glendasan are in the uplands of central Wicklow, west of Wicklow and northwest of Rathdrum. The area, as the crow flies, is just 35 km south of Dublin. The old mines are now in the Wicklow Mountains National Park, and were mined extensively for lead (as well as silver, and later zinc) in the 19th and 20th centuries. See links in reference list to the Glens of Lead and Wicklow Mountains National Park web sites. Paleozoic sediments in the region are cut by the S-type granitoid rocks of the Leinster batholth, the largest Caledonian intrusion in the British Isles. The 1500 km2 batholith consists of five domed plutons, and has been dated at around 405 Ma (Stillman, 2001, pp.164-169). There is strong shear zone development along the border between host metasediments and the Leinster granite (Reavy, 2013, pp.300-302). Numerous veins along the contact of granite and host mica schist supported the mining industry.

Right: Pyromorphite, as a coating of beautiful green sub-mm crystals on a pale, greyish-white matrix of vuggy silica. From the Susanna mine, Leadhills district, Scotland (a locality that has also produced yellow pyromorphite). Some 70 veins were worked in an area of just 8 km2, around the adjacent villages of Leadhills and Wanlockhead, in the Lowther Hills of the Southern Uplands of southwest Scotland. Though there was early interest in gold, lead mining rose rapidly in importance in the second half of the 18th century (Gillanders, 1981). Galena was the primary lead ore mineral but an interesting range of secondary minerals (of copper, zinc and lead) developed later. Over 60 mineral species are known from the district, where mineralization was confined to host units of greywacke and mudstone. Pyromorphite is found on most of the local mine dumps, but unusual orange and red varieties of pyromorphite were reported only in the Susanna mine (Gillanders, 1981, quoting the great Scottish mineralogist M.F. Heddle, author of the 1901 classic The Mineralogy of Scotland).

Samples shown here are from David Joyce (specimens 14607 and 28979; the latter formerly P091471 of the Tony Steede collection), 2022.

"Rock of the Month # 252, posted for June 2022" ---

Pyromorphite

is a phosphate of the apatite group, ideal formula Pb5(PO4)3Cl. The mineral formula contains essential chlorine: a variant termed iodopyromorphite was described, but discredited. Crystals are hexagonal, often somewhat barrel-shaped. Phosphates are often brightly coloured (e.g., Oelkers and Valsami-Jones, 2008). Pyromorphite is no exception. Bright green hues are typical, but some samples are yellow or brown. Dense, as one would expect for a lead mineral, specific gravity 7.04, so pure specimens feel very heavy for their size. Pyromorphite and other Pb-bearing members of the apatite group may exhibit fluorescence (Robbins, 1985). Known for more than 200 years, the mineral name is from the Greek for "fire" and "form", alluding to the crystalline shapes assumed by melted globules of the mineral upon cooling.

At the time of writing (May 2022), there were 182 records mentioning pyromorphite in the MINLIB bibliography, extending back to 1849. In recent decades, and with new sources of fine specimens from China, pyromorphite and its "cousin" mimetite are sought-after by collectors, along with other colourful species such as smithsonite, rhodochrosite, malachite and fluorite. Thus examples are to be found through the pages of the Mineralogical Record, often in thematic collection issues (71% of the MINLIB records on pyromorphite cite this beautifully-illustrated journal).

Notable localities for pyromorphite, starting with examples in the British Isles, include:

  • Leadhills-Wanlockhead district, Scotland (Gillanders, 1981; Moore, 2017)
  • County Wicklow, Ireland
  • Wheal Alfred and Herodsfoot mines, Cornwall
  • Derbyshire (local name: "green linnets": Braithwaite, 1983)
  • Roughton Gill and Driggith mines, Caldbeck Fells, Cumbria (Cockbain, 1968; Cooper and Stanley, 1991; Wilson, 2010; Polityka, 2016).
  • Bwlch-Glas mine & Ysbyty Ystwyth, Cardiganshire, Wales
  • Wheatley and Brookdale mines, Pennsylvania, USA
  • Bunker Hill mine, Idaho, USA (yellow and green)
  • Daoping mine, Guangxi, China (green to yellow)
  • Broken Hill mine, NSW, Australia

A number of interesting pseudomorphs after pyromorphite (or mimetite) have been described from various localities. The replacement minerals include galena (Wheal Hope, Cornwall: Moore, 2013; Kautenbach mine, Germany: Wilson, 2015, p.738) and the Pb-Al phosphate plumbogummite (Roughton Gill: Wilson, 2010; Yangshuo mine, Guilin, Guangxi, China: Wilson, 2020). Pyromorphite may also carry inclusions of rutile (Champion mine, Mono county, California).

References

Braithwaite,RSW (1983) Minerals of the Derbyshire orefield. Mineral.Record 14, 15-24.

Cockbain,AG (1968) Lead apatite solid-solution series. Mineral.Mag. 36, 1171-1173.

Cooper,MP and Stanley,CJ (1991) Famous mineral localities: pyromorphite group minerals from the Caldbeck Fells, Cumbria, England. Mineral.Record 22, 105-121.

Gillanders,RJ (1981) Famous mineral localities: the Leadhills-Wanlockhead district, Scotland. Mineral.Record 12 no.4, 235-250.

Glens of Lead web pages (accessed on 07 February 2022).

Moore,TP (2013) The Royal Cornwall Museum and the Philip Rashleigh Collection, Truro, Cornwall, England. Mineral.Record 44 no.4, 449-462.

Moore,TP (editor) (2017) Mineral Collections in California. Mineral.Record 48 no.4, supplement, 296pp.

Oelkers,EH and Valsami-Jones,E (2008) Phosphate mineral reactivity and global sustainability. Elements 4 no.2, 83-87.

Polityka,J (organizer) (2016) Mineral Collections in the American Northeast. Mineral.Record 47 no.4, supplement, 460pp.

Reavy,J (2013) Field Trip 15. The Wicklow Mountains. In "Geology of Ireland, a Field Guide" (by Meere,P, MacCarthy,I, Reavy,J, Allen,A and Higgs,K), Collins Press, 372pp., 298-306.

Robbins,M (1985) Fluorescence in pyromorphite and other lead apatites. Rocks & Minerals 60 no.6, 293-296.

Stillman,CJ (2001) Caledonian igneous activity. In "The Geology of Ireland" (Holland,CH, editor), Dunedin Academic Press, Edinburgh, 531pp., 145-178.

Wicklow Mountains National Park (accessed on 07 February 2022).

Wilson,WE (editor) (2010) The Lindsay Greenbank Collection: Classic Minerals of Northern England. Mineral.Record 41 no.1, supplement, 148pp.

Wilson,WE (2015) Collector profile: Robert Gilmor, Jr. of Baltimore (1774-1848). Mineral.Record 46, 735-748.

Wilson,WE (compiler) (2020) Mineral Collections in Arizona. Mineral.Record 51 no.1, supplement, 200pp.

Graham Wilson, posted 28-29 May 2022, added locality details on 01 June 2022 .

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