Chlorophyte Bar

Chlorophyte Bars are crafted from 6 Chlorophyte Ore, an end-game Hardmode ore which can be found in the Underground Jungle, or grown in mud.

Crafting all Chlorophyte equipment, excluding the arrows, bullets, Spectre equipment and Shroomite Bars, requires 288 Chlorophyte Bars, or a total of 1,728 Chlorophyte Ore.

Trivia
This could also be a reference to chlorophyll in chloroplasts in plant cells