From what i have red and looking at photos the hammer stone's have a well defined "Groove" and polished. I don't see that on your stone. Fred think about going to the book store and buy good book on artifacts lots and lots of good reading and photos. Good luck
Hammerstone and Peckstones will show visible signs if usage. You will see pecked sections and on most you will see flat spots and areas of cortex that where not utilized in the process and most likely for finger holds.