Chalcocite

specimen number:
2262193

location:
Bristol Mine, Hartford Co., Connecticut, USA

description:

Steel gray semi lustrous crystals of chalcocite, the prominent crystal double terminated in measuring 2.0 cm in length, in a cluster without matrix. This is in good condition. Crystallized completely all around as shown in the video. The specimen comes with a previous antique data card that gives an acquisition date in 1962. Really choice for this old locality.

The Bristol Copper Mine, located in Hartford County, Connecticut, is celebrated by mineralogists as one of the world's premier localities for exceptional, well-crystallized specimens of chalcocite. Geologically, the deposit sits along the western border fault of the Connecticut Rift Valley, where Triassic-age sedimentary sandstones and conglomerates contact Paleozoic metamorphic schists. Hydrothermal fluids migrating along this major fault zone deposited rich copper mineralization within the fractured rocks, producing chalcocite as spectacular, sharp, metallic blue-black to dark gray orthorhombic crystals, often forming complex twins or thick, tabular plates associated with bornite, chalcopyrite, and quartz. Historically, the deposit was discovered in 1780, but formal mining and open-cut quarrying did not begin until 1837 under the Bristol Mining Company. The mine experienced its most productive era between 1847 and 1853 under the management of Professor Benjamin Silliman Jr. of Yale University, before structural difficulties and financial troubles led to its closure in 1857, followed by brief, unsuccessful attempts to reopen the shafts in the 1890s and during World War I. Through 2026, the long-abandoned site remains historically significant, and the magnificent Bristol chalcocite specimens preserved in museum collections worldwide are considered benchmarks for the crystal development of the species.

Questions about this specimen?
Send an email or call us: 314-341-1811.