Mattheddleite

mattheddleite

leadhillite

susannite

macphersonite

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Formula: Pb5(SiO4)1.5(SO4)1.5Cl
Nesosilicate (insular SiO4 groups), ellestadite group
Specific gravity: 6.96 calculated
Hardness: 3½ to 4½
Streak: White
Colour: Creamy white to pinkish
Environments:

Hydrothermal environments

Mattheddleite is a supergene mineral lining cavities in quartz which contain other oxidised lead minerals in the oxidation zone of lead-zinc deposits. Associated secondary minerals include caledonite, lanarkite, cerussite, anglesite, pyromorphite, hydrocerussite, leadhillite, susannite and macphersonite (Dana, HOM, Mindat).

Localities

At Roughton Gill south vein, Balliway Rigg, Caldbeck, Allerdale, Cumbria, England, UK, specimens of mattheddleite were collected from a highly oxidised galena vein. The mattheddleite occurs as drusy crusts lining small cavities and as minute acicular crystals seldom exceeding 0.2 mm in length scattered on other supergene minerals. The most common associations are with lanarkite, caledonite, leadhillite and susannite (JRS 11.18).

At Red Gill Mine, Roughton Gill, Caldbeck, Allerdale, Cumbria, England, UK, mattheddleite has been found associated with caledonite, leadhillite, susannite and lanarkite, and also anglesite and bindheimite. The mattheddleite typically occurs as drusy crusts and radiating sprays of minute colourless to white hexagonal crystals terminated by a sharp point, up to 0.5 mm in length, but they are typically less than 0.1 mm long (JRS 11.39-40).

At Roughton Gill mine, Roughton Gill, Caldbeck, Allerdale, Cumbria, England, UK, mattheddleite is very rare, having only been noted on a single 4 cm specimen, where it lines mm-sized cavities as sprays of minute needles less than 0.1 mm. The matrix is iron-stained quartz-galena and associated minerals include susannite, cerussite and hydrocerussite. On the reverse of the specimen is yellow pyromorphite. Although the specimen was found on the 90 fathom dumps, it is very similar to material from Higher Roughton Gill and the possibility of it having originated there cannot be dismissed (JRS 14.16).

In museum specimens from the type locality, Leadhills, South Lanarkshire, Scotland, UK, mattheddleyite occurs as drusy crusts of prismatic crystals up to about 0.4 mm long, often in cavities on its own, but also associated with other minerals, including lanarkite, cerussite, hydrocerussite, caledonite, leadhillite, susannite and macphersonite. Scotlandite crystals occasionally occur on velvety mattheddleite, but much of the ‘mattheddleite like’ mineral associated with scotlandite here is anglesite (AM 73.929, JRS 12.55-56).

In Wales, UK, mattheddleite always forms late in the paragenetic sequence. It is invariably associated with both caledonite and leadhillite group minerals (MW).

At Eaglebrook mine, Ceulanymaesmawr, Ceredigion, Wales, UK, crystals of mattheddleite to 0.15 mm have been observed encrusting laurionite. Associated supergene minerals include anglesite, caledonite and probable susannite-leadhillite, within a matrix of highly oxidised galena and limonite replacing ferroan dolomite and chalcopyrite (MW).

At Frongoch Mine, Devil's Bridge, Ceredigion, Wales, UK, crystals of mattheddleite to 0.25 mm have been found associated with susannite and caledonite (MW).

At Esgairhir mine, Tal-y-bont, Ceredigion, Wales, UK, crystals of mattheddleite to 0.2 mm overgrow caledonite with associated leadhillite (MW).

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