I have what I believe to be an Indian Artifact from Michigan called a celt but Im not really sure?

It is about four inches length wise and two inchs across. It appears to be sharpened at one end like an axe but without notches. It is similar to Indian celts I looked at on ebay and other websites but I just want to know what I should look for in a authentic celt Indian artifact such as if real celts are only from certain types of stone.