Mining and Quarrying

While unsuited for agriculture, serpentine barrens have long attracted attention because of the unusual minerals to be found there. At the edge of serpentine outcrops, metamorphic reactions with the surrounding rock often form deposits of steatite or soapstone. This soft, easily carved rock was used by the Native inhabitants to make cooking vessels and ornaments, which were traded along river networks. Where they survive, these soapstone quarries are carefully guarded archaeological sites.

The serpentine was also of interest to European inhabitants. In 1609, Henry Hudson saw the green color of a serpentine outcrop in Hoboken and hopefully concluded it to be a copper or a silver mine. In the 1820s, several locations were worked for magnesite (MgCO3), which was used to make epsom salts. This activity largely ceased in the 1870s when an alternative process using German kieserite proved more economical; the magnesite mines at Goat Hill were last worked in 1921. Other localities were worked for talc (ground steatite) and asbestos, although the latter was never abundant.

The bulk of mining activity on the serpentine barrens was associated with chromite (FeCr2O4). While chromium is now principally used in steel alloys, during the nineteenth century, it was mainly used to produce chrome yellow pigment. Isaac Tyson, Jr., (1792–1861), a Baltimore Quaker merchant, was the first to seriously exploit these deposits. He recognized the presence of the heavy, black chromite in rocks in the Bare Hills, a serpentine outcrop in Baltimore County, in 1810, and began mining ore and exporting it to England for processing. He continued to search for sources of ore, and in 1826, began buying land and mining chrome in other parts of the serpentine belt. Tyson ultimately obtained either mining rights or outright ownership over most of the serpentine barrens in Pennsylvania and Maryland, and erected a chemical plant in Baltimore for producing potassium dichromate (K2CrO3) for pigment.

Chrome production from eastern serpentine rapidly supplanted the prior sources of chrome in Siberia, which suffered from isolation and shortages of labor. "Rock chrome" was mined conventionally by shafts and stopes: the Wood Mine, in Lancaster County across Octoraro Creek from Goat Hill, probably the deepest, was worked to a depth of 720 feet. "Sand chrome" was obtained by placer mining; dense grains of chromite deposited in the bed of streams eroding the serpentine could be separated from lighter materials, which were washed away to concentrate the chromite. Both placer and shaft mining took place through about 1880, when the Tyson Mining Co. shifted its supply to more cheaply mined ore from serpentine in California. Due to high demand for chromium, some mining took place near the end of World War I and again at the beginning of World War II. 

Pods of sodium feldspar, a mineral useful for pottery production, occur within the serpentine barrens. This material was quarried extensively during the early twentieth century, up until about World War I. Many of the large water-filled pits scattered on the barrens are old feldspar quarries. The "Mystery Hole" at Nottingham County Park is probably the largest one: feldspar quarried here was sent by rail to a grinding mill in Brandywine Summit, Pennsylvania. Dumps from these quarries continued to be worked over for lower-grade feldspar through until about the Great Depression.

Finally, serpentine was occasionally quarried for use as a building stone. This is most noticeable in the West Chester group of barrens, where many old farmhouses can be found made of serpentine quarried locally before the Civil War. Serpentine tends to fracture and is difficult to cut without crumbling: the only deposit worked successfully on a large scale was Brinton's Quarry, in the West Chester group. Serpentine enjoyed an architectural vogue in the eastern United States from about 1870 to the late 1890s, and most of the demand was supplied by Brinton's Quarry. Smaller quarries in the West Chester group, the Bare Hills, and on Nottingham Barrens supplied material for a few local structures. Unfortunately, serpentine weathers very poorly, especially when exposed to acidic air pollution, and many of these structures have been demolished or required extensive restoration.

All of this mining activity left its mark on the landscape. In addition to the exposed rock and rubble created as pits were dug and dumps were piled, steam pumps to dewater mine shafts and quarries may have been fed by local timber. At least one accidental fire in the early twentieth century at Nottingham Barrens was started by quarry workmen.

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