Malachite replacing Cuprite

specimen number:
8701017

location:
Chessy, Villefranche-sur-Saone, Rhone, Auvergne-Rhne-Alpes, France

description:

A set of two sharp octahedral crystals of cuprite, these now replaced by green malachite. Classic material for this French locality. The size provided is in average between the two pieces.

The Chessy-les-Mines district, located near Lyon in the Rhone department of France, is the type locality for azurite and is famous for its unique copper mineralization. Geologically, the deposit is a pyritic massive sulfide body hosted within Devonian volcanic and sedimentary rocks that underwent intense secondary oxidation. A hallmark of this locality is the occurrence of malachite replacing cuprite, typically forming sharp pseudomorphs where vibrant green malachite has completely substituted the original deep red octahedral or cubic cuprite crystals. These specimens, often referred to as "chessylites" in older literature when referencing the associated azurite, are prized for their distinct geometric forms and velvety textures. Historically, mining and quarrying at Chessy began in the mid-15th century, with the most significant period of copper and sulfuric acid production occurring between 1810 and 1877 under the direction of the mines' most famous administrators. While the main underground workings were abandoned by the late 19th century due to the depletion of the ore and flooding, the site remains an iconic European mineral locality.

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