Datolite

specimen number:
2062237

location:
Delaware Mine, Keweenaw Co., Michigan, USA

description:
Classic example of what is known as a datolite nodule. Cut and polished on one face.

The Delaware mine, situated at the historic site of Delaware in Keweenaw County, Michigan, was a notable underground copper mining operation located on the northern slope of the historic Keweenaw Peninsula copper range. Geologically, the deposit is a native copper system localized within the amygdaloidal flow tops of the Mesoproterozoic Portage Lake Volcanics, specifically targeting the native copper mineralization embedded within the basaltic Allouez Conglomerate bed. Late-stage, low-temperature hydrothermal fluids migrating through these porous volcanic and sedimentary sequences precipitated native copper alongside secondary minerals, including dense, microcrystalline datolite nodules that formed inside vesicles and open voids. Historically, formal exploration began in 1847 under the Northwest Mining Company, followed by a succession of reorganizations into the Delaware Mining Company and the Conglomerate Mining Company, which constructed a massive mill and extensive shaft infrastructure during peak activity in the early 1880s. Despite heavy capital investment, the low grade of the copper ore led to the permanent cessation of commercial industrial mining in 1887, though the site was later developed as a popular historical tourist attraction in the mid-twentieth century. Through 2026, while industrial copper extraction has long ceased, the site remains a major geological reference point for collectors studying copper-district mineral paragenesis, with the surrounding rock piles celebrated for producing highly prized porcelain-like datolite nodules that reveal spectacular pink, yellow, and white color patterns when cut and polished.

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