Chromite

specimen number:
2102340

location:
Wood Chromite Mine, Lancaster Co., Pennsylvania, USA

description:
Massive chromite throughout this matrix with serpentine. Neat locality example for the species.

The Wood chromite mine, situated along the Horseshoe Road loop of the Octoraro Creek within Little Britain Township of Lancaster County, Pennsylvania, United States, is historically celebrated as one of the most prolific and significant sources of chromium in nineteenth-century North America. Geologically, this unique underground deposit is hosted within the State Line Serpentine District, part of an ancient, highly metamorphosed ophiolite suite where a massive wedge of oceanic mantle rocks was thrust onto the continental margin during Paleozoic mountain-building events. Localized magmatic segregation processes within the ultramafic peridotite host rocks concentrated massive, tabular bands of high-grade chromite ore, which later underwent extensive hydrothermal alteration to form spectacular secondary mineral coatings of vibrant green zaratite, kammererite chlorite, brucite, and hydromagnesite within regional shear fractures. Historically, the deposit was discovered around 1828 by the pioneering mineralogist Isaac Tyson Jr., who recognized the commercial value of the heavy black surface stones and immediately initiated systematic open-pit and deep underground shaft development. Operated heavily by the Tyson Mining Company and later the Chrome Mining Company, the facility expanded into a massive industrial complex utilizing a vertical shaft that reached an impressive depth of 720 feet with multi-level horizontal galleries, supplying a near-monopoly of the global chromium supply for paint pigments and chemical manufacturing until the importation of cheaper foreign ores and the exhaustion of easily accessible underground veins forced the permanent cessation of all commercial extraction in November 1882.

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