Marcasite with Sphalerite

specimen number:
9892166

location:
Blackstone Mine, Shullsburg, Wisconsin, USA

description:
Classic specimen from Wisconsin with bright lustrous rounded golden crystal groupings of marcasite measuring to 2.5 cm in diameter standing up from a matrix that is mostly covered with small black crystallized sphalerite. In very good condition.

The Blackstone Mine, located near Shullsburg in Lafayette County, Wisconsin, sits within the historic Upper Mississippi Valley Zinc-Lead District, a famous Mississippi Valley-Type mineralized region. Formed during the Paleozoic era, low-temperature hydro-thermal fluids migrated through fractured Ordovician limestone and dolomite host rocks, depositing rich primary sulfide mineralization along pitch and flat structural fractures. First developed as an underground operation during the early twentieth century by companies like Vinegar Hill Zinc Company and later expanded mid-century by Eagle-Picher, the mine served as a major commercial producer of zinc and lead ore until operations permanently ceased in 1979. Mineral collectors hold specimens from the Blackstone Mine in high regard for their iconic regional mineral assemblage, which features lustrous brown to reddish-brown sphalerite, sharp brassy pyrite and marcasite, galena, and well-formed calcite scalenohedrons set on dense, grey-brown dolomite matrix.

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