Ordinary Corundum: A Chester County Mineral
by Thomas M. Walsh
Many people are familiar with corundum as an abrasive used in the manufacture of such household items as emery boards, emery cloth and some whetstones. Most people are not aware that they may own corundum jewelry. Gem quality red corundum stones are known as rubies and gem quality blue corundum stones are known as sapphires. There will be no tales of rubies and sapphires in this article. At the risk of being abrasive, the article will focus on the mining of the ordinary industrial-quality corundum.
Corundum Hill is located in Newlin Township north of Rt 842 and southwest of Embreeville, with Rt 162 and the west branch of the Brandywine completing the parameters. This area is known as the “barrens.” As its name implies, it is not a lush woodland area that we associate with many sections of Chester County. Instead, it is an area of stunted trees and grasslands that battle to survive in the calcium deficient and thin serpentine soils. Today, the overall name for this area is the Unionville Barrens. The ancient geology of the barrens caused the Corundum Hill area to develop when long ago igneous pegmatite intrusions came in contact with the even older serpentine rock. The result created areas of highly mineralized contact zones featuring corundum and other associated minerals. Between 1830 and 1900, Corundum Hill would attract both those wishing to supplement their income or even make a small fortune selling corundum, and mineral collectors wishing to own or trade some specimens found in this area.
Corundum is second only to diamonds in hardness (9 out of 10 on the original Mohs scale). It has a high specific gravity (3.9 – 4.1) and its crystals are hexagonal and sometimes they are tapered. There has been a shift over the years to manufactured abrasives and recent decades show an increase in the use of silicon carbide (9 – 9.5 Mohs). In Chester and neighboring Delaware County, “crystalline and massive forms” have historically been found. Ronald A. Sloto in this 2009 book The Mines and Minerals of Chester County gives us the newest and one of the best sources for the activities at Corundum Hill. Please note that he covers mineral and mining locations on a municipal basis. For Corundum Hill, Sloto has listed more than 40 minerals that have been identified, as well as 5 minerals that have been discredited. Sources indicate John and Joel Bailey found the first corundum in Chester County in the 1820s. Early corundum finds included “large masses lying on the surface; these were a nuisance to farmers plowing their fields. Smaller boulders were used in stone fences.” Some farmers even dug holes deep enough to bury the stones below the plow zone. By 1832 mineral collectors began visiting Corundum Hill. The celebrated mineralogist William W. Jefferis first visited in or around 1837. Also, in 1836 or ’37 an English plate glass manufacturer sent a representative to the United States to search for glass cutting minerals. As a follow-up to that visit, mineralogist Lewis White Williams had purchased some property in the barrens near Unionville. Included in this purchase was a “well that had been abandoned when the diggers struck corundum.” Williams also “collected loose crystals and small masses of corundum.” William’s farm changed hands numerous times and is also known as the Patterson Mine. It probably ceased operations in the late 1860s when Samuel N. Pusey, Spencer Chandler, and George Ball purchased the farm. The new owners working elsewhere on the farm began what is known as the Chandler-Ball Mine.
A “mass of corundum was estimated to weigh 150 tons and exposed by trenching.” It was described as “30 feet long, 5 to 10 feet wide and 15 feet long.” Work at the Chandler-Ball site continued until 1881 when the location was abandoned. The Pierce Mine opened on Joshua Pierce’s farm in 1875. He shut down in 1879 when water in the shaft caused many problems. Records show Pierce sold three tons in 1881 with an additional supply of five tons suggesting that it was mined before the shutdown in 1879. His son Nathan opened a new location (probably on the same farm) in 1885. Outside operators ran the site in 1886-87 and 1890. Records for 1888-89 and for the shutdown date for the site are presently unknown. The Elliot Mines are named for Captain John W. Elliot. He operated at least two to four locations in the barrens at various times. Between 1879 and 1892, Elliot managed the operations for at least a half-dozen corporations with names such as The Sapphire Mining Company, Northbrook Mining Company, and American Corundum Mining Company.
In 1881 the Unionville Corundum Company purchased Howell Baily’s farm. Capt. Elliot added new machinery and new buildings. “In 1887, the company reported production of 600 to 700 pounds of ore per day. By 1889, the shaft was 160 feet deep plus and plans were made to sink two new shafts.” A two-story 30-foot by 60-foot crusher was also built here.
In 1890, Capt. Elliot and his partners leased the Pierce farm and between 1892 and 1895 the Corundum Hill mines had ceased operations. For a period of approximately 55 years, Corundum Hill was the corundum mining center for the United States. Ore was taken from the ground by open pit, shaft mining, and drift mining. Some material was broken on site for shipment by wagon to the nearest Wilmington and Reading station (from north to south: Embreeville, Glen Hall, and Northbrook). Many of the early shipments of corundum went to England and other European countries as the domestic markets slowly grew. Some corundum was crushed at Kennett Square and by the end of the mining period Capt. Elliot had a crusher at one of his operations as mentioned previously. By the mid-1890s mining was over except for the mineral collectors search for a fine specimen from Corundum Hill.
You can contact Tom Walsh at: tmwalsh318@aol.com.
Editor’s note: Much of the corundum area cited in this article is part Natural Land’s ChesLen Preserve. As a reminder rock and mineral specimens may not be picked up, dug and/or removed from ChesLen property.