Yes, its a bone. I bet it was broken with an axe, look at the chip slightly down from the cut off point. I can't tell from what creature, you might go back to the spot and look for more evidence.
I did find it in an area where there is a indian camp that I found and check this, I found an ax head also.... Would be cool if it was the ax but what are the odds?
That does look like a Arachaic type of tool, possiably a hand axe? looks like it has been worked.. Nice find.. and I find all types of Petrified bone frags like that along the coast and on the rivers..