Luminite

Luminite is an ore that drops from the Moon Lord Boss, usually in stacks of 70-90. It can be used to craft Luminite Bars, which can then be used to make many end-game items, such as the Solar, Nebula, Vortex, and Stardust tools. It is also used to create armor sets.

Trivia

 * It may well be that this is a reference to the CBBC childrens' show The Sparticle Mystery, where there exists a mineral called luminite which boosts any energy going through it.