Pyrochroite with Zincite, Willemite

specimen number:
2133326

location:
Sterling Mine, Ogdensburg, New Jersey, USA

description:
Black masses and crystalline pyrochroite on matrix with zincite and willemite.

The Sterling Hill mine, located in Ogdensburg, Sussex County, New Jersey, is a historic underground operation renowned for its unique stratabound zinc deposit. The local geology is characterized by highly deformed Mesoproterozoic metamorphic rocks of the Reading Prong, specifically the Franklin Marble formation, which hosts a folded, stratiform orebody composed of unusual non-sulfide zinc minerals, primarily franklinite, willemite, and zincite. These iron-manganese-zinc oxides and silicates formed through the metamorphism of seafloor exhalative sedimentary precipitates. Small-scale surface quarrying and localized mining for iron and zinc began at the site in the late 18th century, but large-scale industrial underground development accelerated after 1897 when multiple competing operations consolidated into the New Jersey Zinc Company. A modern vertical shaft was sunk in the 1950s, allowing for continuous, high-tonnage extraction of zinc ore to supply the domestic manufacturing sector. Due to declining ore reserves, falling metal prices, and a severe corporate legal dispute over tax assessments, commercial mining operations officially and permanently ceased on March 28, 1986.

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