C-12 shaped charge

The UNSC C-12 Shaped-charges or C-12 SCs are used mainly for heavy demolitions and can also be used as weapons. This compound is extremely dangerous and very volatile. A small 4x4x4 inch cube alone can level a five story building in seconds. It's solid, but malleable enough where it can be shaped or bent into different forms to stick to surfaces better and fit into tight spots and is detonated with electric-shock detonator sticks or remote detonators. They also could be mounted on the nose of a pelican dropship as a breaching charge

C-12 is also hefted in medium sized backpacks called "Damage Packs" or "Blow Packs". Two Damage Packs contain enough C-12 to blow through three meters of UNSC standard armor plating.

Trivia

 * In the present day there is a very powerful and effective explosive called C-4, possibly a precursor to C-12.
 * During World War II there was a reasonably powerful explosive called C-2, which is a precursor to C-4 and possibly to C-12.
 * C-12 may also be related to C-7.