Grand Meadow Chert

Grand Meadow chert is a humble Minnesota rock with layers of history. Used for centuries by Indigenous people to make tools and weapons, it can now be seen and appreciated at the Grand Meadow Chert Quarry/Wanhi Yukan Archaeological and Cultural Preserve in Grand Meadow.

Mineral Content. Chert is a sedimentary rock composed of micro- or cryptocrystalline quartz, the mineral form of silicon dioxide.

Appearance. Chert is essentially another word for flint. Grand Meadow chert typically occurs as a nodule that contains a mineral within a mineral. The nodule has an outer, sandy brown shell of calcium carbonate concealing the distinct gray or olive-gray chert within. The chert has a thin, sharp profile and flakes easily, making it especially well suited to tool and weapon fabrication in preindustrial times.

Geologic Origin. The Grand Meadow Chert Quarry/Wanhi Yukan site showcases the primary source of this chert. Millions of years ago, oceans covered southeastern Minnesota. The remains of shellfish integrated into the sediment, which compressed over time and became limestone, seen today in the region’s towering bluffs. Eventually the ocean receded, leaving tidal pools that chemically changed over time. The glassy silica-rich skeletons of aquatic lifeforms in these pools eventually crystallized into the quartz that composes Grand Meadow chert. The quarry site is the highest point of the Grand Meadow chert bed, serendipitously exposing the site for Indigenous discovery and usage. This is not Minnesota’s only chert type. More than two dozen cherts are endemic to the state, and over 70 have been found as a result of trade among Indigenous peoples.

Human Uses. According to Tom Trow, lead archaeologist at the site, Grand Meadow chert has been found at archaeological sites in 52 counties in Minnesota, as well as in Iowa, South Dakota, and Wisconsin. Chert was a “high-value commodity for all Indigenous people,” says Trow. “Everybody needed a piece of chert every day.” Grand Meadow chert was the best-quality material in Minnesota for making buffalo hide scrapers, he says, and was used widely for this purpose. It can also be polished and made into jewelry. The oldest Grand Meadow chert tool found in Minnesota was with a bone that was carbon-dated as 8,000 years old.

Historic Site. After surface deposits were depleted, Indigenous people dug deep pits to harvest chert. The nearly 100 pits on display at the eight-acre public quarry site, where visitors can take a self-guided tour spring through fall, are among more than 2,000 pits that once covered 200 acres. The site was added to the National Register of Historic Places in 1994. The Dakota title of the preserve, Wanhi Yukan, means, “There is chert here.”