Botallackite - Encyclopedia

    Class : Halides
    Subclass : Oxychlorides
    Crystal system : Monoclinic
    Chemistry : Cu2Cl(OH)3
    Rarity : Very rare

Botallackite is an extremely rare copper chloride, a polymorph of atacamite and paratacamite with which it is usually associated. It is a secondary chloride that is formed at the expense of copper minerals subjected to the action of chlorine solutions or sea water. It is also present in certain slags immersed in the sea, and in the weathered part of black smokers ocean bottoms. It is a mineral which owes its name to its site of discovery : Botallack in English Cornwall. Botallackite forms encrustations of tiny fibrous crystals that are pale green to bluish green, rarely blue.

Main photo : Botallackite from Levant Mine, Cornwall, England © Gianfranco Ciccolini

Botallackite from Cligga Head, Cornwall, England © Jay I. G. Roland
Botallackite from Cligga Head, Cornwall, England © Simone Citon
Botallackite from Herzog Julius scoria, Saxony, Germany © Rolf Luetcke
Botallackite from Cligga Head, Cornwall, England © Knut Eldjarn

Botallackite in the World

The finest specimens come from its type locality : Botallack (Cornwall, England), and from neighboring deposits in the same district of Saint Just, but tiny crystals also exist at the Argent mine, in South Africa. Botallackite is quite common in the ancient submerged slags of the Lavrion (Greece).

Botallackite in France

Botallackite is reported at Cap Garonne (Var) as well as in the slag of Poullaouen and Crozon (Finistère).


No known twin for this mineral species.

Fakes and treatments

No fake inventories for this mineral species.

Hardness : 3
Density : 3.6
Fracture : Irregular
Trace : Blue-green

TP : Translucent to transparent
RI : 1.775 to 1.846
Birefringence : 0.071
Optical character : Biaxial +
Pleochroism : Low
Fluorescence : None

Solubility : -

Magnetism : None
Radioactivity : None