Pickaxe is the only item that has the ability to mine gems from boulders in the Gnome Mines.
One is usually found in the Gnome Mines, it can also be rarely found in the dungeon, or wished for.
It has the highest damage bonus against large of all weapons (+100%). This doesn't make it a good weapon because of how slowly you attacks become. It is the slowest weapon in the game. 50-100% slower than a regular Greatsword