Actinolite

specimen number:
2102402

location:
French Creek Mines, Chester Co., Pennsylvania, USA

description:
The top of matrix is mostly covered with acicular crystallized green actinolite, this is the variety often called byssolite. In good condition.

The French Creek mines, located near Saint Peters in Warwick Township, Chester County, Pennsylvania, comprised a famous underground iron and copper operation known for producing exceptional mineral specimens. Geologically, the deposit is a pyrometasomatic iron-copper skarn situated within the Triassic-aged Newark Basin, where a massive diabase sheet intruded and metamorphosed Paleozoic limestone beds and Precambrian gneisses. Hydrothermal fluids altered the host rocks to form rich zones of magnetite and chalcopyrite alongside an array of secondary minerals, famously yielding sharp, dodecahedral magnetite crystals, octahedral pyrite, and capillary coatings of fibrous actinolite within localized cavities. Formal commercial mining began at the site in 1845 to extract iron ore, eventually expanding under the direction of the E. and G. Brooke Iron Company into a highly structured underground system accessed via the No. 1 and No. 2 shafts. The operation provided steady metallurgical feed for regional blast furnaces, with production peaking during World War I before deep-level structural challenges, rising water management costs, and the depletion of high-grade reserves forced the permanent closure of the mines in 1928.

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