Actually, what appears to be thorns are part of the buds on this tree.
This is one of my favorite kinds of trees, although it is not native to northern Indiana. This tree has lovely strings of sweet smelling white blossoms in the spring. It leaves the ground beneath covered in long seed packets that rattle when you shake them in the fall.
As you may have guessed by the look of the seed packets, the Black Locust is a member of the pea family. It is just a big pea making some great hard wood.