C-12 shaped charge
From Halopedia, the Halo wiki
The UNSC C-12 Shaped-charges or C-12 SCs are used mainly for heavy demolitons, and can also be used as weapons. This compound is extremely dangerous, and is very volatile. A small 4x4x4 inch cube can level a 5 story building. It's solid, and shapable into different forms to stick to surfaces better, and is detonated with electro-shock detonator sticks, or remote detonators.
