Neptunium

Neptunium is a block in Lunacraft which is a radioactive, olive green block.

General Information
Neptunium is crafted from sixteen Blue Crystal blocks, which in the scanner are shown to be Aluminium Oxide. Note that in real life Aluminium Oxide cannot be used to make Neptunium, which is in itself an element.

It's only current purpose in the game is to make Energy Orbs, and can be used as a building block.