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Cotunnite nymonh.jpg
Category Halide mineral
(repeating unit)
Strunz classification 3.DC.85
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pnam
Unit cell a = 7.6222(5) Å,
b = 9.0448(7) Å,
c = 4.5348(4) Å; Z = 4
Color Colorless to white, pale green, pale yellow
Crystal habit As elongated, flattened prismatic crystals; in aggregates of radiating sprays; granular, crustiform or pseudomorphs
Cleavage Perfect on {010}
Fracture Subconchoidal
Tenacity Slightly sectile
Mohs scale hardness 2.5
Luster Adamantine, silky to pearly
Diaphaneity Transparent to opaque
Specific gravity 5.80
Optical properties Biaxial (+)
Refractive index nα = 2.199 nβ = 2.217 nγ = 2.260
Birefringence δ = 0.061
2V angle Measured: 67°
Solubility Slight in water
References [1][2][3]

Cotunnite is the natural mineral form of lead(II) chloride with formula PbCl2.

It was first described in 1825 from an occurrence on Mount Vesuvius, Naples Province, Campania, Italy.[2] It was named for Domenico Cotugno (Cotunnius) (1736–1822), Italian physician and Professor of Anatomy.[1]

It was first recognized in volcanic fumarole deposits. It occurs as a secondary alteration product in lead ore deposits. It has also been reported as an alteration of archaeological objects that contain lead.[1][4]

It occurs in association with galena, cerussite, anglesite and matlockite in the Caracoles, Chile. At the Tolbachik volcano on the Kamchatka Peninsula, Russia it occurs with the rare to uncommon minerals tenorite, ponomarevite, sofiite, burnsite, ilinskite, georgbokite, chloromenite, halite, sylvite and native gold.[1]