Promethean arm-blade

The fan dubbed "blade arm" is a melee weapon utilised by Promethean Knights in the upcoming Halo installment, Halo 4. Promethean Knights sometimes use the blade to slice at opponents after dashing forwards for an attack, as shown int he E3 game play demo. Not a lot is known about the weapon, what it is made of, or if it is usable by Spartans.