The Gravity Hammer (known as the Fist of Rukt[1]) is the personal weapon of the Brute Chieftain, Tartarus, and he alone can wield the mighty hammer. At 2.682m[2] it not only serves as an excellent melee weapon, but can alter gravity to move objects and living beings around.
It may contain shards from the mysterious crystal found in the book Halo: First Strike, as the crystal could alter gravity.