Corundum

specimen number:
2262147

location:
Corundum Hill, Newlin, Chester Co., Pennsylvania, USA

description:
A loose tapering hexagonal crystal of corundum. Choice locality example for the species.

Corundum Hill, located near Unionville in Newlin Township, Chester County, Pennsylvania, represents a significant historical locality for industrial abrasive minerals. Geologically, the deposit is situated within a belt of serpentinite and associated ultramafic rocks where hydrothermal alteration and contact metamorphism of aluminous sediments resulted in the formation of corundum-bearing veins. The corundum at this site typically occurs as gray, brown, or blue-gray hexagonal crystals and massive granular blocks embedded within a matrix of chlorite and margarite. Historically, mining and quarrying activities at Corundum Hill began in the late 1830s after the initial discovery of loose crystals in the soil, with organized commercial production starting around 1848. The mines were a primary domestic source of abrasive-grade corundum used for grinding wheels and emery products throughout the mid-to-late 19th century, particularly under the operation of the Unionville Corundum Company. While the discovery of higher-grade deposits in the southern United States and the advent of synthetic abrasives led to the decline and eventual cessation of mining by the early 1890s, the site remains a classic Eastern U.S. locality.

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