Luminite Bar

Luminite Bars are a type of bar used to craft all four sets of endgame armor and tools as well as other endgame items. The only way to obtain it is to craft it from Luminite, which is dropped from the Moon Lord, at an Ancient Manipulator. Each time the Moon Lord is killed, it drops enough Luminite for 17-25 bars ( 21-27 in Expert/Master mode).

Crafting all items (excluding ammunition) requires a total of 317 Luminite Bars (1,268 Luminite; requires defeating the Moon Lord 15–19 / times). Crafting all items pertaining to one type of Lunar Fragment (i.e., armor, wings, pickaxe, and hamaxe) requires 68 Luminite Bars (204 Luminite) in addition to 85 of the Lunar Fragment; this requires defeating the Moon Lord only 3 / times.

Gejakite Bars
Accidentally left in the game when Luminite Bars were added was a placeholder item called Gejakite Bars. The only way to obtain it was using an Inventory Editor, or by somehow obtaining -1 and buying it from the Traveling Merchant.

It worked seemingly as an equivalent to Luminite Bars, being used interchangeably in all crafting recipes that used Luminite Bars. It sold for 119. It was removed in 1.3.0.2, and any Gejakite Bars that still existed were replaced with Luminite Bars.

Trivia

 * Luminite Bars are the most profitable bars in the game, selling for . However this is not the most profitable way to sell extra Luminite, that prize going to its corresponding Monolith at 20 introduced in the 1.4.0.1 update
 * Prior to Desktop 1.4.0.1, Luminite Bars were the only bar that could stack past 99, up to 999. In other versions of the game, this still applies.