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