Photosynthesis

Chlorophyte ore grows in the Underground Jungle's mud once hardmode begins, and needs a pickaxe axe or drax (Drax Attax) - i.e. post-mechs - to mine. Spelunker potions light it up bright green. One block pops it; several stacks build the Chlorophyte and Turtle sets, so keep digging. It regrows in mud, and a small farm of mud blocks seeded with one ore quietly prints more.