A mattock it like a pickax. It has an pick on one end and a flat curved section on the other end. See here for pics (no pun intended).

Yes, Thorin's cousin Dain, from the Iron Hills, brought over 500 grim drawf warriors, clothed in a short hauberk, fine mail on their legs, a steel helm on their heads. They had small bucklers slung at their backs, weilded large double handed mattocks, and had small short swords at their sides. Their beads were forked, plaited, and thrust into their belts. And their faces were grim.

But that's just from memory.

--Matt