Hello /sci/

I have been metal detecting near confirmed alluvial gold works in the golden triangle of Victoria. I wasn't getting much signal at all adjacent to a worked crop of quartz but then I got a good signal from this large stone.

Can anyone help me identify what sort of rock it is? It seems like really dense sediment that breaks away like dust. I'm in the process of breaking it open to look at the insides.

The only hot rocks I've found have been obviously ferrous in form and colour but this looks well rounded and of sedimentary nature