Mill Creek chert

Mill Creek chert is the tough, coarse-grained, brown or gray chert of Union and Alexander counties in southern Illinois, and it is the best-known stone for Mississippian hoes. It occurs in large, flat, elliptical nodules in creek beds and hilltop soil, probably from the Ullin limestone. Colour ranges from white and gray through brown, yellow and reddish-brown to pale blue or black, often with banding that follows the outline of the nodule. The texture is grainy and rough, but a big nodule needs little trimming to become a large biface, and it survives hard use. Mill Creek bifaces were made near the quarries and traded widely across the central Mississippi and Ohio valleys between A.D. 900 and 1400.

Nodules probably come from the Ullin Limestone formation of the Mississippian. They occur as large, flat, elliptical nodules in creek beds or hilltop residuum in Union and Alexander counties, Illinois. The nodules are thick and lenticular, so only light edge trimming and cortex removal turns them into large preforms or bifaces, and the stone is physically durable (Cobb 2000, cited by Barry).