Galena with Chalcopyrite

specimen number:
2013417

location:
Sweetwater Mine, Viburnum Trend, Reynolds Co., Missouri, USA

description:
From the late 1980s, a wonderful grouping of sharp lustrous cubic galena crystals with minor attached breccia matrix. This is in super condition all around. Golden crystals of chalcopyrite are scattered throughout.

The Sweetwater Mine in Reynolds County, Missouri, is part of the Viburnum Trend, one of the most important lead producing regions in the United States. The mine was developed in the 1960s during the expansion of large scale exploration for lead deposits in southeastern Missouri. It exploits Mississippi Valley type ore bodies hosted in Cambrian dolomite, with galena as the primary ore mineral. Operated by the Doe Run Company, the mine has been a major source of lead and associated minerals such as sphalerite and chalcopyrite. The Sweetwater Mine remains an important part of the regions modern mining industry.

A cast in minerals forms when one mineral fills a void left by the dissolution of another, preserving the external shape of the original crystal. In the case of pyrite after anhydrite, the original anhydrite crystals dissolved and left open spaces that were later filled by pyrite. The pyrite took on the shape of the original anhydrite crystals, creating a cast rather than a true replacement.

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