Nearly all the United States’ greatest structures—the Empire State Building, the Washington National Cathedral, the Metropolitan Museum of Art, to name just a few—owe much of their grandeur to a humble source that keeps on giving: a band of limestone in south-central Indiana.
This geological richness stretches back at least 345 million years, when the tropical waters of a warm inland sea ground up the remains of calcite-bearing invertebrates, forming carbonate sand—not the more common quartz sand—fated to lithify as some of the world’s most prized limestone. During this period, Indiana was a “carbonate factory,” says Todd Thompson, director of the Indiana Geological and Water Survey and Indiana’s state geologist. Cycles of deposition and erosion winnowed this precious carbonate bed to a 35-mile stretch of prime quarry between what are now Bloomington and Bedford.
The Hoosier State’s first commercial limestone quarry was established in 1827. Demand for limestone skyrocketed in the 1890s, after massive urban fires razed buildings across Chicago and Boston. Indiana limestone was the ideal rebuilding solution, flame-resistant and up to the country’s first building codes, says Todd Schnatzmeyer, executive director of the Indiana Limestone Institute of America. Architects and sculptors quickly came to love the stone—dubbed “the Nation’s Building Stone”—for several reasons. It’s chemically pure and consistent, at over 97 percent calcium carbonate, which makes it highly uniform; it’s a freestone—you can cut, carve or mill it in any direction; and it stands the test of time, because its uniformity gives it the same strength in all directions. What’s more, compared with other high-quality deposits, such as those in Alabama, Indiana limestone is both accessible and vast. “Indiana limestone has gone into literally tens of thousands of building projects across North America and the world,” Schnatzmeyer says.
Thousands of projects have gone up in the 21st century using this American bedrock, from the rebuild of the Pentagon after the 9/11 attacks to the new Yankee Stadium to 15 Central Park West, designed by Robert A.M. Stern. As the renowned architect once put it, Indiana limestone, “even on a gray day … seems to glow.”