Millerite

specimen number:
2013637

location:
Hall's Gap, Kentucky, USA

description:

An open geode half lined with sparkling crystals of quartz and very rich metallic acicular crystallized millerite. This is excellent for this old locality. In great condition.

The Hall's Gap locality, situated along a steep road cut of US Highway 27 just south of Stanford in Lincoln County, Kentucky, United States, is a world-famous mineral occurrence renowned for producing some of the finest, most delicate millerite specimens ever discovered. Geologically, this classic site is hosted within the Mississippian-age Warsaw-Salem Formation, a marine sedimentary sequence consisting of argillaceous limestone, dolostone, and shale that contains thousands of hard, silica-rich chalcedony and quartz geodes. During late-stage diagenesis, low-temperature hydrothermal fluids circulating through the sedimentary strata precipitated pristine, hair-like acicular needles and tightly coiled brassy-yellow clusters of the nickel sulfide mineral millerite within the hollow interiors of these geodes, frequently associated with secondary minerals such as chalcopyrite, pyrite, galena, sphalerite, dolomite, and calcite. Historically, the locality was exposed during major highway construction and widening projects in the mid-twentieth century, quickly becoming a premier destination for academic geologists and mineral collectors alike who excavated the road cut during its peak collecting era from the 1960s through the 1880s and 1990s. While never operated as a commercial, industrial mine or quarry for metal extraction, the site functioned as a highly prolific, non-commercial mineral mining locality until safety concerns, property rights, and concrete reinforcement of the unstable road cut heavily restricted active digging.

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