Nigel Molesworth wrote:

If you are planning to bash this with a sledge hammer, forget it.

Actually, that can work quite well. I needed to break up some large
flint rocks when I was digging out a soakaway underneath my
now-redundant in-ground swimming pool, and this was the only way I
could think of to reach 4 feet or so under the pool with the required
force. Despite the advice I received not to hit it, I made up a wooden
box that fitted over the tamping end to contain any steel bits that
might break off, lightly wedged the tool in place, donned a face mask
and hit away. After some effort, the flint broke up nicely and I
fished out the small bits with a modified garden hoe. But you are right
, it is hot work.

CRB