Cotunnite

Cotunnit, also lead chloride, chemically lead (II ) chloride, is a rare mineral from the mineral class of halides. It crystallizes in the orthorhombic crystal system with the chemical composition of PbCl2 and forms prismatic along and elongated along { 010 } flattened crystals of up to two millimeters in size, as well as skeletal -like crystals, granules, masses or crusts of white color.

Etymology and history

Cotunnit was first discovered in 1825 by Monticelli and Covelli in the type locality, Mount Vesuvius near Naples in Italy. They named the mineral after the Italian anatomy professor Domenico Cotugno ( 1736-1822 ).

Classification

In the classification by Strunz Cotunnit is counted among the Oxihalogeniden. After the 8th edition forms a group together with Fiedlerit, Laurionite, Paralaurionit and Pseudocotunnit. In the 9th edition, it forms a separate subgroup of oxyhalides, hydroxyhalides and related double halides with lead, but without copper.

In the classification by Dana it forms with Hydrophilit and Coccinit a subset of crystal- water-free and -containing halides with a ratio of metal to halide of 1:2.

Education and Locations

Cotunnit can form in several ways. In volcanoes, it is a sublimation product. In addition, it is formed by the weathering of galena, lead-containing archaeological finds or slags under saline conditions. It is depending on the locality associated with galena, cerussite, anglesite and matlockite ( Caracoles, Chile ) or Tenorite, Ponomarevit, Sofiit, Burnsit, Ilinskit, Georgbokit, Chloromenit, halite, [ sylvite ] and gold ( volcano Tolbachnik, Russia).

In addition to the type locality a number of other localities are known. These include the Hohe Tauern in Austria, Caracoles and Challacollo in Chile, Sainte -Marie -aux -Mines in France, Roehrnbach, Richelsdorf, food, Recklinghausen and Helbra in Germany, Laurion in Greece, Tuscany in Italy, the Tolbachik in Russia, Wanlockhead, lead Hills and other localities in the UK and the U.S. states of Arizona, Massachusetts and Utah.

Crystal structure

Cotunnit crystallizes in the orthorhombic crystal system, space group Pnam ( Raumgruppen-Nr. 62) with the lattice parameters a = 7.62 Å, b = 9.04 Å and c = 4.53 Å and four formula units per unit cell. Cotunnit is eponymous for the Cotunnit structure, in addition to lead (II ) chloride salts, such as more barium chloride, calcium or lead crystallize (II ) bromide.