Trinitite

Trinitite is a type of nuclear waste created by the fallout of a nuclear explosion. It is essentially nuclear glass.

Obtention
It is obtained by detonating a dirty bomb, nuclear bomb, or poison bomb near sand (both normal and red). When its ore is mined without silk touch, it drops a piece of trinitite.

Trinite is the only material that can be made back into its ore form, though this won't cause any exploits.

Uses
Trinitite is highly radioactive, meaning it can be used as fuel in the Radiation-Powered Engine and made into nuclear bullets.

It can be made into radioactive blocks.

Its ore form can be smelted into "Trinity Glass". Similar to uranium or polonium glass, it is mostly a novelty. It is lime colored.

Trivia

 * You can buy trinitite in real life. It is not particularly dangerous (anymore),
 * "Trinity Glass" is also a real thing, but it has no relation to a refined form of trinitite at all.