Polybasite

specimen number:
2273027

location:
Neihart, Cascade Co., Montana, USA

description:
Very choice and rare locality example for the species, a cluster of crude semi lustrous polybasite crystals without matrix. The specimen comes with a previous label from the collection of Barbara and Forrest Cureton as shown at the end of the video.

The Neihart mining district, situated in the Little Belt Mountains of Cascade County, Montana, is a historic silver-producing area centered on a series of deep fissure veins. Geologically, these high-grade hydrothermal veins cut through complex Precambrian metamorphic rocks, including gneiss and schist, and are associated with Late Cretaceous to Paleocene igneous intrusions. The ore mineralogy consists of primary silver sulfides and sulfosalts, such as polybasite and pyrargyrite, alongside galena, sphalerite, and chalcopyrite. Silver was first discovered in the canyon in 1881, sparking a major mining boom that led to the establishment of prominent operations like the Silver Dyke, Queen of the Hills, and Minnelusa mines. Production peaked during the late 1880s and early 1890s, but the silver panic of 1893 severely crippled local industry, causing operations to become highly intermittent until a brief resurgence in the 1920s and 1930s, with most formal commercial mining winding down by the 1940s.

Polybasite is a complex silver copper antimony sulfosalt mineral that crystallizes in the trigonal system, often forming striking pseudohexagonal tabular crystals. Geologically, it occurs as a primary mineral in low-to-medium temperature hydrothermal veins, typically representing one of the final silver-bearing phases to precipitate out of late-stage ore fluids. The mineral is visually characterized by its iron-black to dark gray coloration, metallic luster, and characteristic dark red internal reflections when viewed in thin splinters or under intense light. In rich silver districts like Neihart, polybasite serves as a major economic component of the high-grade unoxidized silver ore zones, frequently occurring in close association with related silver sulfosalts, quartz, barite, and carbonates.

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