cotunnite

{{infobox mineral | name = Cotunnite | category = Halide mineral | image = Cotunnite nymonh.jpg | imagesize = 260px | alt = | caption = Cotunnite | formula = PbCl2 | IMAsymbol = Cot | molweight = | strunz = 3.DC.85 | dana = | system = Orthorhombic | class = Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) | symmetry = 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 | colour = | habit = As elongated, flattened prismatic crystals; in aggregates of radiating sprays; granular, crustiform or pseudomorphs | twinning = | cleavage = Perfect on {010} | fracture = Subconchoidal | tenacity = Slightly sectile | mohs = 2.5 | luster = Adamantine, silky to pearly | streak = | diaphaneity = Transparent to opaque | gravity = 5.80 | density = | polish = | opticalprop = Biaxial (+) | refractive = nα = 2.199 nβ = 2.217 nγ = 2.260 | birefringence = δ = 0.061 | pleochroism = | 2V = Measured: 67° | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = Slight in water | impurities = | alteration = | other = | prop1 = | prop1text = | references = }} Cotunnite is the natural mineral form of lead(II) chloride (PbCl2). Unlike the pure compound, which is white, cotunnite can be white, yellow, or green. The density of mineral samples spans range 5.3–5.8 g/cm3. The hardness on the Mohs scale is 1.5–2. The crystal structure is orthorhombic dipyramidal and the point group is 2/m 2/m 2/m. Each Pb has a coordination number of 9. Cotunnite occurs near volcanoes: Vesuvius, Italy; Tarapacá, Chile; and Tolbachik, Russia.

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