Franklinite with Calcite, Willemite

specimen number:
2072094

location:
Sterling Hill, Ogdensburg, New Jersey, USA

description:
Black octahedral crystals of franklinite to 0.5 cm in size embedded up on a massive white calcite matrix with crystals of willemite. Brightly fluorescent. Minimal damage present.

The Sterling Hill Mine is located in Ogdensburg, Sussex County, New Jersey, and is world-renowned as one of the most significant mineral localities on Earth. Geologically, it is a stratiform zinc deposit hosted within the Precambrian Franklin Marble. The ore body, along with the nearby Franklin deposit, formed approximately 1.3 billion years ago through a complex process involving seafloor hydrothermal activity followed by intense high-grade metamorphism during the Grenville Orogeny. Unlike most zinc deposits that consist of sulfides, Sterling Hill is unique because its primary ore minerals are oxides and silicates, specifically franklinite, willemite, and zincite. Historically, mining in the area dates back to the 17th century, though large-scale industrial operations for zinc production occurred primarily from the mid-1800s until the mine's closure in 1986. Today, the site operates as the Sterling Hill Mining Museum and is famous for its "Rainbow Tunnel," where the walls glow with brilliant green and red fluorescence under ultraviolet light due to the presence of manganese-activated willemite and calcite. With over 350 different mineral species identified, many of which are found nowhere else, Sterling Hill remains a site of immense scientific importance and a premier destination for mineral collectors globally.

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