That looks like Mill Creek flint from So IL. It was used extensively by the Mississippians from Cahokia and traded widely. It was used mainly to make spades and hoes. It’s very tough material and holds up well. Mill Cr artifacts have been found at the Mississippian Aztalan site in WI. This is a Mill Cr spade.
Here’s another one. This one still has a lot of cortex. The Mill Cr nodules are large, flat and tabular. A very convenient shape for making spades.