Hi Bigjilm, I have recorded many aboriginal sites and scatters of flaked stone. I can see an unmistakable bulb of percussion mark where one flake was hammered off your stone and faces where other flakes have been hit off. If its golf ball sized it is the left over core after all the flakes have been hammered off. When the rock being worked gets down to about that size it gets difficult to hammer off the desired flakes and the core is discarded. The rock looks a little worn and varnished so I think the stone was probably worked a couple thousand years ago at least
So in my humble opinion i'm pretty sure you have a aboriginal core
The raw material is probably chert but could be a form of chalcedony also.
Cheers RedDirtDigger