Willemite after Descloizite with Mimetite

specimen number:
2312474

location:
Chah Milleh Mine, Anarak, Nain Co., Isfahan, Iran

description:
A cluster of large spiky descloizite crystals, this completely replaced by crystallized willemite. Neat pseudomorph specimen that is complete all around and in great condition. Orange yellow micro crystals of mimetite are scattered throughout.

The Chah Milleh Mine, situated in the historic Anarak mining district of Nain County, Isfahan Province, Iran, is a renowned polymetallic deposit with a legacy of artisanal and small-scale extraction targeting base and precious metals. Geologically, the deposit is set within a complex zone of Precambrian to Paleozoic metamorphic basement rocks and younger volcanic-sedimentary sequences that have been heavily intruded, faulted, and subjected to intense hydrothermal activity and secondary weathering. Mineralogically, the mine is famous for producing an array of exceptional secondary lead, zinc, and copper species, yielding good specimen material including vibrant wulfenite, mimetite, and rare alteration assemblages.

Pseudomorphs occur when one mineral replaces another while preserving the original crystal shape of the precursor species, a process driven by changing chemical conditions in the surrounding aqueous environment. A striking example from this region is willemite after descloizite, where zinc-silicate solutions permeated the voids of the mine and completely dissolved or replaced earlier crystal clusters of lead-zinc vanadate. This transformation maintains the sharp, distinctive, tree-like or prismatic habit of the original descloizite while coating or converting the structure into sparkling willemite, frequently accompanied by later generations of bright orange mimetite or wulfenite.

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