Tim,
looking at the granular structure of the rock ..it would seem to be a sedimentary type ..like sandstone. I believe a great number of stone headed clubs were of the 'volcanic type...such as granite,quartz and flint etc. much harder and denser.
As sedimentary rock is deposited in layers it tends to have alot of inherent 'faults' which breaks/chips easily. However, if your foe is also limited to sedimentary rock clubs then.....game on
Regards David