Cumengeite - Encyclopedia
Class : Halides
Subclass : Oxychlorides
Crystal system : Tetragonal
Chemistry : Pb21Cu20Cl42(OH)40
Rarity : Very rare
Cumengeite is a very rare secondary mineral in copper deposits, typical of arid climates in a chlorinated environment (evaporite lagoons and marine coastlines); it therefore shares the deposits of boleite and pseudoboleite. It is also found in the slag of foundries submerged at sea. It was named in honor of Edouard Cumenge, a French mining engineer at Boléo where the first specimens were discovered. It appears in octahedral or cubo-octahedral crystals, of a magnificent indigo blue hue, often forming epitaxial aggregates with boleite : each face of the boleite cube supports a tetragonal pyramid of cumengeite giving very original complex buildings which evoke twins with six crystals. It is a mineral highly sought after by collectors.
Main photo : Cumengeite from Amelia Mine, Boleo, Mexico © Kiyoshi Kiikuni
Cumengeite in the World
Twinning
No known twin but a very unique epitaxy on boleite.
Fakes and treatments
No fakes listed for this mineral species.
Hardness : 2.5
Density : 4.65
Fracture : Irregular
Streak : Blue
TP : Translucent
RI : 1.926 to 2.041
Birefringence : 0.100
Optical character : Uniaxial -
Pleochroism : Visible
Fluorescence : None
Solubility : Nitric acid
Magnetism : None
Radioactivity : None