Once in a while we pick up black rocks hoping that they are black jasper and they turn out not to be black jasper at all. This is what happened here. This piece of black rock turned out to be too soft to be jasper, a fact we found out after tumbling when we did a hardness check. We did a hardness check after tumbling because it was far bigger than this before we put it in the tumbler.
 
This is basalt, i.e. old lava bed. It is an interesting shape and, for some reason, it is a satisfying rock to hold. If you want a rock to rub while you stim then this is a good un.