The gravite longsword is a main hand melee weapon released along with the Dungeoneering skill. It requires 55 Attack and 45 Dungeoneering to wield. It can be purchased from the rewards trader for 40,000 Dungeoneering tokens, which would realistically require a Dungeoneering level of 64 to obtain.
The gravite longsword has 30,000 charges of combat (a minimum time of 5 hours). Once the charges run out, it will break and become unusable until repaired by the rewards trader at Daemonheim. When first purchased, it will have a 20% charge. Repairs are made incrementally in 1% portions, and the cost of recharging can be paid in two ways: coins, or a combination of coins and Dungeoneering tokens.