COTUNNITE

    Class : Halides
    Subclass : Chlorides
    Crystal system : Orthorhombic
    Chemistry : PbCl2
    Rarity : Rare

Cotunnite is a rare supergene mineral from arid climate lead deposits, located in or near evaporitic basins. Like many chlorides, it is also a fumarolic mineral known in beautiful crystals, notably at Vesuvius. It was named in honor of the Italian physicist Domenico Cotugno, professor of anatomy at the University of Naples. The crystals are elongated flattened prisms of small size (2 mm maximum), sometimes united in radiated aggregates, in slags cotunnite can also form transparent pseudo-hexagonal crystals. Cotunnite also appears in crusts or massive ; it is colorless or white, sometimes yellowish or greenish.

Main photo : Cotunnite from Vesuvius, Naples, Italy © OT. Ljøstad

Cotunnite in the World

In addition to Vesuvius, which provided the most beautiful specimens, cotunnite is notably reported in the deposits of the Atacama Desert (Chile), in several American lead deposits in Arizona and Colorado, and in Peru (Pasto Bueno). In Europe, it is present in the gossans of the Scottish lead veins of Leadhills and Wanlockhead. The large dumps of the Laurion lead deposit (Greece) also show beautiful crystallizations of cotunnite, the chlorine necessary for its formation being provided by the spray from the nearby sea.

Right photo : Cotunnite from Lavrion, Greece © Gerhard Brandstetter

Cotunnite in France

In France, cotunnite is reported in Ste-Marie-aux-Mines (Haut-Rhin), at the Buisson mine (Lozère), at the Cougnasses mine (Hautes-Alpes) as well as at Cap Garonne (Var). 

Twinning

A twin is known on {120} but only on synthetic crystals.

Fakes and treatments

No fake identified for this mineral species.


Hardness : 1.5 to 2
Density : 5.8
Fracture : Sub-conchoidal
Streak : White

TP : Transparent to translucent
RI : 2.199 to 2.260
Birefringence : 0.061
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : Water, hydrochloric acid, nitric acid

Magnetism : None
Radioactivity : None