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Formula: Pb21Cu20Cl42(OH)40.6H2O
Choride
Epitaxy: Parallel overgrowths of cumengeite on crystals of boleite and
pseudoboleite
Crystal System: Tetragonal
Specific gravity: 4.656 measured, 4.66 calculated
Hardness: 2½
Streak: Sky-blue
Colour: Indigo blue
Solubility: Soluble in nitric acid
Environments
Hydrothermal environments
Fumeroles
Cumengeite occurs in the secondary zone of
lead deposits, formed through reaction of chloride ions with
primary sulphides, in smelter slag immersed in sea water and
of exhalative origin near a volcanic fumarole
(HOM).
Localities
In Vesuvius fumaroles, Mount Vesuvius, Somma-Vesuvius Complex, Naples, Campania, Italy, the first Italian occurrence
of cumengeite was found. Italian cumengeite occurs in a fumarole, which is unique for the mineral.
Associated minerals include tenorite,
gypsum and cotunnite
(MM 69.1037-1045, HOM).
At the type locality, the Boleo District, Santa Rosalía, Mulegé Municipality, Baja California Sur, Mexico,
cumengeite is associated with boleite,
pseudoboleite, atacamite,
anglesite, cerussite,
phosgenite and gypsum
(HOM).
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