It coud be a gunflint. If it was, the shape of the edges at the upper and lower ends as pictured is important. One edge or the other at a minimum should be wedge shaped or show signs of having been so. My flints look as shown in top view and I knapp the edge until they get too short to stay in the jaws reliably or allow any steel of the cock (hammer) to hit the frizzen. The sharpened edge changes position as it is repeatedly renewed to be sharp and square to the frizzen. Of course, as lock sizes varried greatly the flint could be rotated 90 degrees and the same would apply. Hugh