Cotunnite is the natural mineral form of lead(II) chloride (PbCl<sub>2</sub>). 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/cm<sup>3</sup>. 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.<!--conflicting data w/ the following page (i.e.: hardness): http://rruff.geo.arizona.edu/doclib/hom/cotunnite.pdf-->
It was first described in 1825 from an occurrence on Mount Vesuvius, Naples Province, Campania, Italy.
It occurs in association with galena, cerussite, anglesite and matlockite in the Caracoles, Chile. At the Tolbachik volcano on the Kamchatka Peninsula, it occurs with the rare to uncommon minerals tenorite, ponomarevite, sofiite, burnsite, ilinskite, georgbokite, chloromenite, halite, sylvite and native gold.