Mimetite with Calcite
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Mimetite with Calcite from Naica, Chihuahua, Mexico, measuring 85 × 58 × 45 mm and weighing 223 grams. A good combination piece from a mine far more famous for a very different mineral altogether.
Mimetite, lead chloroarsenate Pb5(AsO4)3Cl, occurs as a secondary mineral in the oxidised zone of the Naica lead-zinc-silver skarn deposit, forming where arsenic released by weathering sulfide ore combines with lead, with Calcite a common later-stage gangue mineral in the same system. Naica is best known internationally for the giant Selenite crystals of its deep Cave of the Crystals, formed under very particular hydrothermal conditions, but the mine's shallower, cooler and more oxidised workings have also produced collector-grade secondary minerals including Mimetite from the same broadly skarn-related mineralising system.
A Naica Mimetite is a reminder that a single famous deposit can carry more than one story worth collecting, well beyond the giant crystals that made the mine's name internationally. This piece carries a double provenance, the David Vince Collection and Ruth Coulsell Collection.