One of your empty hands (your choice) becomes encased in a stony shell. You cannot hold anything in the affected hand while the spell lasts, but you can use the hand to make unarmed strikes that don't provoke attacks of opportunity. You deal 1d6 points of damage when you strike with the stone fist, plus you gain a +1 bonus on your attack and damage rolls, increasing by +1 for every three caster levels above 3rd (to a maximum of +5 at caster level 15th). Any feats or class abilities you have that affect your unarmed strikes apply to attacks you make with the hand and a monk using this spell can attack with the hand as though it was a special monk weapon. When you strike an unattended object with the hand, your damage is doubled.