Kryptonite (Earth-5261)

Kryptonite is a green radioactive mineral, remnant of the World Engine's failed terraformation. Found inside the Black Zero in the Indian Ocean, it was manufactured by Lionel Luthor and LexCorp to use against Superman, the mineral being extremely deadly to Kryptonians, and also rendering them powerless against regular enemies.

Creation
When General Dru-Zod and the Sword of Rao managed to arrive on Earth from the Phantom Zone with the help of Faora-Ul and Superman, they quickly settled the World Engine over the Indian Ocean to terraform the human planet so they could build a new Krypton from the ashes. As Superman battled Zod and his soldiers, however, the Engine was able to terraform a small portion of the land above the ocean before it was destroyed by the United States Air Force, which caused the creation of Kryptonite.

Discovery
Kryptonite slivers were discovered by a team of LexCorp explorers and researchers led by John Corben on September 20th, 2011. Corben and the team then collected the slivers they found and had it sent back to Metropolis in the United States through the ''White Portuguese. ''

Corben arrived with the material at the LexCorp Building, delivering it personally to CEO Lex Luthor. Luthor theorized the material could be harmful to Kryptonians after he tested it near the body of the late Dru-Zod, which he had acquired from S.H.I.E.L.D. as he was one of their consultants at the time.