Chalcocite

specimen number:
2102376

location:
Chimney Rock Quarry, Somerset Co., New Jersey, USA

description:
Interesting locality example for the species, metallic pseudo-hexagonal crystals of chalcocite measuring to 0.5 cm in size on matrix. In good condition. Collected in November, 1991.

The Chimney Rock quarry, situated near Bound Brook in Bridgewater Township, Somerset County, New Jersey, is a major industrial aggregate operation highly esteemed by regional mineralogists for producing exceptional specimens of copper and zeolite minerals, including native copper, chalcocite, prehnite, and golden calcite. Geologically, the quarry is excavated into the massive Early Jurassic-age First Watchung Mountain basalt, a extensive trap rock lava flow that overlies the sedimentary red mudstones of the Brunswick Formation within the Newark Basin rift system. Mineralization developed as low-temperature hydrothermal fluids circulated through extensive vesicle zones, cooling fractures, and structural faults within the basalt, depositing secondary silicates and copper minerals inside hollow vugs and pockets. Historically, primitive copper mining began in the adjacent ridges as early as 1754 under various ventures like the Bridgewater Mining Company and the American Copper Company, which worked underground tunnels intermittently through 1909 before high operational costs forced a total cessation of copper extraction. The modern open-pit aggregate quarrying operation was established on the site in 1886 by William Haelig to supply crushed basalt stone for regional road infrastructure, expanding continuously through the twentieth century under subsequent ownership, and it remains a highly active trap rock producer managed by the Stavola Company through 2026.

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