In Missouri it is permissible to collect some mussel shells if you mind the limits. I needed some mussel shell tools for a program I do with kids on resource use. It is a compare and contrast thing demonstrating that we and Native Americans both have to live off resources. The natives directly harvested and processed their items is the main real difference.
Below is an shell adze I recently finished. In the other pic is a woodland/Mississippian era hoe (simple and easy to make) a plant cutting tool, a spoon and a necklace.
Shell is harder to work with than bone but the results are worth it.