knitting and breaking rocks

I'm woking on some experimental archaeology and learning how to make stone tools. The basics are as follows... You take rocks like this (not this particular one, it very very old)
and rocks like this
and you whack the rocks together to break them together and make smaller sharper rocks. the best bits i got were these...

so obviously it needs work. I have been slowly making progress on the Kilt hose and they are a couple inches from the heel.