One thing I'd like to point out is that while Granite Armor does reduce recharge, damage, and movement speed (not to mention no jumping whatsoever), it does not reduce accuracy. Also, it doesn't protect against Psionic attacks.
I'd also like to comment on Mineral armor. In CoH, I wouldn't dream of playing a 40+ stoner without it, but I haven't seen which villain groups use psionic attacks. For my own DM/Stone build, i'm taking a wait and see approach.
if I recall correctly, attacks that deal multiple types of damage can be defended by powers that defend against one type. So if someone tries to hit you with a fire sword attack, which does Fire, and say, Lethal, Rock Armor has a chance to stop it from hitting at all since it defends against Lethal. The reason Mineral Armor was advantagious is that there are few psionic attacks that I know of which have multiple damage types. I might be wrong about this, or it may have changed, or the aspartame worms in my brain could have gotten to me.
