Susannite

susannite

leadhillite

mattheddleite

macphersonite

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Formula: Pb4(SO4)(CO3)2(OH)2
Compound carbonate, trigonal paramorph of leadhillite (monoclinic) and macphersonite (orthorhombic)
Specific gravity: 6.52 calculated
Hardness: 2½ to 3
Streak: White
Colour: Colourless to greenish or yellowish
Environments:

Hydrothermal environments

Susannite occurs as a secondary mineral in the oxidised zones of hydrothermal lead deposits, formed above 80oC (Mindat, Webmin).

Localities

At Red Gill mine, Caldbeck Fells, Cumbria, England, UK, susannite occurs with cerussite, leadhillite, caledonite, mattheddleite, linarite and queitite (C&S, JRS 11.42).

At Roughton Gill mine, Caldbeck Fells, Cumbria, England, UK, susannite occurs embedded in acicular caledonite (C&S).

At Short Grain, Caldbeck Fells, Cumbria, England, UK, susannite occurs in cavities in massive baryte with leadhillite, caledonite, cerussite and mattheddleite (C&S).
The susannite occurs as rhombs or short prisms with triangular terminations up to 4 mm in length. Larger prismatic crystals up to about 10 mm in length usually bridge the cavities in which they have grown. Small cavities in quartz veinstone are sometimes filled with massive susannite. Susannite is often intimately intergrown with caledonite and mattheddleite. It is not uncommon to find susannite and leadhillite in the same cavity, occasionally associated with macphersonite. Some specimens from Short Grain Low Level have pale blue susannite crystals with white mattheddleite and stout blades of caledonite. Other minerals associated with susannite include plumbojarosite and anglesite (JRS 12.59-60).

At Silver Gill, Caldbeck Fells, Cumbria, England, UK, susannite associated with leadhillite has been found on the ore pile (JRS 8(2).94).

At the type locality, the Susanna mine, Leadhills, South Lanarkshire, Scotland, UK, susannite is a rare secondary mineral in the oxidised zone of hydrothermal lead-bearing deposits, formed at temperatures above 80oC. Associated minerals include leadhillite, macphersonite, lanarkite, caledonite and cerussite (HOM).

Alteration

Heating leadhillite causes it to transform reversibly into susannite in the temperature range from 50 to 82oC (AM 90.1641-1647). Susannite decomposes at about 300oC to the unnamed lead oxysulphate Pb5(SO4)O4 (AM 55.1444-1449).

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