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

No known twin but a very unique epitaxy on boleite.

No fakes listed for this mineral species.