by Mashadar » Sun Mar 06, 2011 3:17 am
It's not related to the type of metal. The hardness of the rock varies greatly.
It should give you a message that ranges from "this rock is just slightly too hard for you to mine" all the way to "you do not even manage to scratch that rock".
That should give you a rough idea of how much more strength you need.
If you can craft a stone axe above q21, you might want to use that instead. It's slower, but it might be enough to mine through that part of rock.