Leadhillite

minerals

lanarkite

susannite

macphersonite

Images
Formula: Pb4(SO4)(CO3)2(OH)2
Compound carbonate, the monoclinic paramorph of susannite (trigonal) and macphersonite (orthorhombic)
Hardness: 2½ to 3
Streak: White
Colour: Colourless to white, grey, yellowish, pale green to blue; colourless in transmitted light
Solubility: Soluble in nitric acid with effervescence, rendering a residue of lead sulphate. Exfoliates in hot water.
Environments:

Hydrothermal environments

Leadhillite is common only in deposits that contain very little carbonate mineralisation. Several localities in the Caldbeck Fells, Cumbria, England, and the Leadhills/Wanlockhead mining field, Scotland, meet this requirement, which is why leadhillite is relatively common there. It is quite rare in the nearby carbonate-rich Pennines (JRS 18.10).
For carbonate concentration slightly lower than atmospheric, cerussite and hydrocerussite can co-exist in alkaline environments, with leadhillite in more acid environments, and anglesite in yet more acid environments. At extremely low carbonate concentrations the rare mineral lanarkite can form in conditions of pH between those for anglesite and leadhillite (JRS 18.11)

Localities

At Tsumeb, Namibia, leadhillite occurs with mimetite and melanotekite (R&M 90.2.185-186).

At Balliway Rigg, Caldbeck, Allerdale, Cumbria, England, UK, leadhillite has been found in cavities in oxidised galena in quartz veins, associated with caledonite, mattheddleite and lanarkite. It is sometimes associated with anglesite, cerussite or linarite (JRS 11.15-16).

At the Red Gill mine, Roughton Gill, Caldbeck, Allerdale, Cumbria, England, UK leadhillite occurs as crusts on quartz associated with numerous minerals including anglesite, linarite, caledonite, bindheimite, cerussite and susannite (JRS 11.38).

At Short Grain, Deer Hills, Caldbeck, Allerdale, Cumbria, England, UK leadhillite is common in the supergene post-mining assemblage, and in some specimens it replaces lanarkite. Crystals are also produced by in situ oxidation in the vein. It is often associated with its paramorphs susannite and macphersonite, and sometimes occurs with scotlandite, native silver or caledonite (JRS 12.54-55).

At Silver Gill, Roughton Gill, Caldbeck, Allerdale, Cumbria, England, UK leadhillite occurs associated with anglesite and caledonite (JRS 8(2).91-92).

At Driggith mine, Caldbeck, Allerdale, Cumbria, England, UK, on the dumps, leadhillite occurs in oxidised galena-bearing fragments associated with caledonite, anglesite and cerussite (JRS 9.23).

At the Brae Fell mine, Roughton Gill, Caldbeck, Allerdale, Cumbria, England, UK, leadhillite occurs associated with anglesite, caledonite, cerussite and linarite (JRS 9.41).

At Whitwell quarry, Derbyshire, England, UK, leadhillite is associated with galena and baryte (RES p138).

At the Manila Mine, Cochise county, Arizona, USA, leadhillite occurs associated with anglesite, and in vugs with caledonite, diaboleite, linarite and lanarkite (R&M 90.4.344).

At the Mammoth-St Anthony mine, Tiger, Pinal county, Arizona, USA, a specimen has been found of leadhillite on and pseudomorph after cerussite (KL p182).

Alteration

Heating leadhillite causes it to reversibly transform into its paramorph susannite in the temperature range from 50 to 82°C.

Stability

The Activity-pH diagram below was calculated for some lead minerals. Boundaries are calculated for constant activity (roughly equivalent to concentration) of (SO4)2- and constant partial pressure (also roughly equivalent to concentration) of CO2, over a range of values of pH and of Cl1- activity. In this case the concentration of CO2 is above the atmospheric value.
Both paralaurionite and leadhillite can be stable at this level of CO2 concentration, although they are not at higher levels. If the concentration of CO2 decreases further the stability field of leadhillite widens to include a greater range of pH (JRS 15.20).

stability Pb 2.jpg

The lead mineral formulae are:
cotunnite PbCl2
phosgenite Pb2(CO3)Cl2
paralaurionite PbCl(OH)
cerussite Pb(CO3)
anglesite Pb(SO4)
leadhillite Pb4(CO3)2(OH)2













The Activity-pH diagram below is similar, but the concentration of CO2 is close to zero, at about 0.01% of the atmospheric value, and the (SO4)2- activity is about 0.5% of its value in the first diagram.
Cerussite does not form in these conditions, the stability field of mendipite is very large, that of leadhillite is small, and mereheadite and plumbonacrite can form, although they are not stable at higher levels of concentration of CO2 (JRS 15.18-23).

stability Pb 5.jpg

The lead mineral formulae are:
cotunnite PbCl2
paralaurionite PbCl(OH)
mendipite Pb3O2Cl2
mereheadite Pb47O24(OH)13cl25(BO3)2(CO3)
hydrocerussite Pb3(CO3)2(OH)2
plumbonacrite Pb5(CO3)3O(OH)2
anglesite Pb(SO4)
leadhillite Pb4(CO3)2(OH)2











Back to Minerals