US Silica Rockwood Pit, Michigan

This pit, south of Detroit, is one of 27 or so across the country operated by US Silica, a company that specializes in mining silica rich sand, the raw material that is turned into glass. Silica is used in a host of other applications, from petrochemical plants to playgrounds, not to mention filtration systems, building materials, abrasives, oil and gas fracking, and foundry mold making. This pit was purchased by the company in the 1940s, and provides a type of sand that has properties favored by sheet glass makers. The sand has been used to make specialty window glass for contemporary art museums and other architectural applications. US Silica was formed from the merger of the Pennsylvania Glass Sand Corporation, and the Ottawa Silica Company, of Illinois, in 1987. Though this site is near the edge of Lake Erie, on the east side of Michigan, the west side of the state, along the shore of Lake Michigan, has a few dozen shoreline dune sites that have been mined for silica sand, making Michigan the third largest producer of the material (after California and Illinois), though fewer than a dozen of these sites remain active. The use of this sand for making molds in the foundries of the midwest, especially the auto industry, was by far the largest use of the sand mined from the dunes along Lake Michigan. Now silica sand is more often mined from pits, including the largest silica sand mine in the nation, at Ottawa, Illinois, also part of US Silica.