Cotunnite

{{Short description|Natural mineral form of lead(II) chloride}}

{{infobox mineral

| name = Cotunnite

| category = Halide mineral

| image = Cotunnite nymonh.jpg

| imagesize = 260px

| alt =

| caption = Cotunnite

| formula = PbCl₂

| IMAsymbol = Cot{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}

| 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 = n_α = 2.199 n_β = 2.217 n_γ = 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 = [http://rruff.geo.arizona.edu/doclib/hom/cotunnite.pdf Handbook of Mineralogy][http://www.mindat.org/min-1141.html Mindat.org][http://webmineral.com/data/Cotunnite.shtml Webmineral data]

}}

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.[http://webmineral.com/data/Cotunnite.shtml Cotunnite]

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.

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.[http://www.mindat.org/loc-203439.html Late-Hellenistic shipwreck, Mahdia, Tunisia, (Mindat locality)]

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.