US highway 27 roadcut

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Halls Gap, Lincoln County, Kentucky, USA

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Key Information

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  • The US Highway 27 roadcut in Halls Gap, Lincoln County, Kentucky, is a notable mineral locality, especially for millerite-containing geodes.

  • It is located about 5 miles south of Stanford, accessible via US Highway 27, in a temperate climate with four distinct seasons.

  • The site features over 30 minerals, with millerite and honessite being particularly uncommon, often found in geodes within the Borden Formation.

  • Research suggests the minerals formed from ancient brines, with the "millerite zone" being a 1.4-meter-thick layer rich in specimens.

  • Discovered in 1964, it has been a collector's site with periods of closure and reopening, currently advised for caution due to safety concerns.

Location and Accessibility

Halls Gap is a small community in central Kentucky, about 30 miles west of I-75 at Mt. Vernon. The roadcut is along US Highway 27, north of the Halls Gap Motel, making it a convenient stop for enthusiasts traveling through the area.

Mineral Highlights

The locality is renowned for its millerite, forming needle-like crystals in geodes, alongside honessite, celestine, calcite, and pyrite. These minerals offer a diverse collecting experience, with millerite's unique occurrence being a highlight.

Geological Context

The site exposes the Halls Gap and Muldraugh members of the Borden Formation, sedimentary rocks from the Mississippian period. The "millerite zone" is particularly rich, suggesting a complex formation process involving ancient brines.

Historical and Cultural Notes

Discovered in 1964, the site has a history of enthusiast-driven collecting, with safety concerns noted due to the overhang. Halls Gap itself is a quaint town, part of Lincoln County, named after General Benjamin Lincoln, adding historical depth to the visit.

Citations