Talloric Alloy
Talloric Alloy is a type of material found on various planets in both Metroid Prime 2: Echoes and Metroid Prime 3: Corruption. This material is extremely vulnerable to concussive Morph Ball Bombs, and cracked or damaged structures that contain the material can usually be destroyed by a single Bomb. Talloric Alloy is often used to cover small tunnels and maintenance hatches, allowing Samus to drop a Bomb then enter through the area with her Morph Ball.
Talloric Alloy seems to be a common material. It exists on many mechanisms and covers used by both the Galactic Federation, Space Pirates, the Chozo, and even Bryyonians. It's origin is unspecified, though as an alloy it must contain some sort of metal within it. It is similar in function to Sandstone and could possibly be what Bomb Blocks are composed of.
