Cotunnite

Cotunnite
Cotunnite
General
CategoryHalide mineral
Formula
(repeating unit)		PbCl2
IMA symbolCot[1]
Strunz classification3.DC.85
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPnam
Unit cella = 7.6222(5) Å,
b = 9.0448(7) Å,
c = 4.5348(4) Å; Z = 4
Identification
ColorColorless to white, pale green, pale yellow
Crystal habitAs elongated, flattened prismatic crystals; in aggregates of radiating sprays; granular, crustiform or pseudomorphs
CleavagePerfect on {010}
FractureSubconchoidal
TenacitySlightly sectile
Mohs scale hardness2.5
LusterAdamantine, silky to pearly
DiaphaneityTransparent to opaque
Specific gravity5.80
Optical propertiesBiaxial (+)
Refractive indexnα = 2.199 nβ = 2.217 nγ = 2.260
Birefringenceδ = 0.061
2V angleMeasured: 67°
SolubilitySlight in water
References[2][3][4]

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.[5]

It was first described in 1825 from an occurrence on Mount Vesuvius, Naples Province, Campania, Italy.[3] It was named for Domenico Cotugno (Cotunnius) (1736–1822), Italian physician and Professor of Anatomy.[2]

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.[2][6]

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.[2]

References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c d Handbook of Mineralogy
  3. ^ a b Mindat.org
  4. ^ Webmineral data
  5. ^ Cotunnite
  6. ^ Late-Hellenistic shipwreck, Mahdia, Tunisia, (Mindat locality)


This article about a specific halide mineral is a stub. You can help Wikipedia by expanding it.