The term used to designate any surviving fragment of the exploded planet Krypton, the home world of Superman. There are five distinct varieties of Kryptonite (green, red, gold, blue, and white), the first three of which are toxic to Superman.
Green Kryptonite, the only variety potentially fatal to Superman, induces lassitude and inertia followed by death if not removed in time from Supermanâ€™s presence. Red Kryptonite inflicts bizarre and unpredictable, albeit temporary and nonfatal, symptoms, as when it divides Superman into twins or transforms him into an infant or a giant ant. Gold Kryptonite would permanently rob Superman of his super-powers were he ever to he exposed to its radiations. These three varieties of Kryptonite are similarly hazardous to Supergirl, Krypto the Superdog, Beppo the Supermonkey, and all other surviving natives of Krypton. Blue kryptonite is toxic only to superpowered Bizarro creatures. White Kryptonite is harmful only to plantlife. (TGSB) Whenever the word Kryptonite appears in the Supermanica without a specific color designation, it is Green Kryptonite, the most common variety, that is being referenced (See Superman [ section 7.1, Kryptonite ])
Full list of every type of Kryptonite that has appeared in the chronicles is as follows:
0. K-Metal: A previously undocumented substance from Krypton (told of in a startling unpublished text from 1940), it has the same weakening effect on Kryptonians as Green Kryptonite, with the additional ability to temporarily grant tremendous strength (and possibly other super-powers) to humans on Earth (this element may be similar to the X-Kryptonite documented in Superman Family No. 203 in 1980, though no chronicle suggests a relationship).
1. Green Kryptonite: Green Kryptonite, is fatal to superpowered Kryptonians but harmless to non-superpowered Kryptonians, It induces lassitude and inertia followed by death if not removed in time from Superman's presence. (TGSB)
2. Red Kryptonite: Red Kryptonite inflicts bizarre and unpredictable—albeit temporary and non-fatal—symptoms, as when it divides Superman into twins or transforms him into an infant or a giant ant. (TGSB) Its effects last only 48 hours and are never repeated in the same way on the same Kryptonian again.
3. Gold Kryptonite: Gold Kryptonite would permanently rob a Kryptonian of his super-powers were he ever to be exposed to its radiations. Phantom Zone parolee Quex-Ul suffered this effect (S No. 157), as did a Lex Luthor-created Superman clone (Act No. 500).( TGSB)
5. White Kryptonite: White Kryptonite is harmful only to plant life, though it can also affect some vareties of microbe. (TGSB)
6. Jewel Kryptonite: Created by Jax-Ur of the Phantom Zone ("That chunk of Jewel K in orbit magnifies our mental commands and converts them into energy beams which detonate any explosive material we desire."). Jewel Kryptonite appears in Act No. 310, Mar 1964: "Secret of Kryptonite Six".
7. X-Kryptonite: Accidentally created by Supergirl, it gives Streaky the Supercat powers beyond those of mere mortal cats. It is later revealed that X-Kryptonite can weaken super-powered Kryptonians as well (SF No. 203/1, Sep/Oct 1980: "The Supergirl from Planet Earth").
8. Red-Green Kryptonite: Red-Green Kryptonite first appears in the story "The Menace of Red-Green Kryptonite!" in Act No. 275, Apr 1961.
9. Anti-Kryptonite: A type of Kryptonite that affects only non-superpowered Kryptonians. Later tales recounting the story of Supergirl and her parents document this isotope (namely how the non-superpowered Krypton survivors in Argo City could be affected by lethal Kryptonite radiation).
10. Slow Kryptonite: Created by Metallo (Roger Corben). It is "able to slow down the rate of particle emissions enough to affect humans as it does Kryptonians" (The Brave and the Bold No. 175, Jun 1981: "The Heart of the Monster"). Although the effect on Batman is agonizing and impressive, the effect (if any) on Kryptonians are not documented.
11. Kryptonite-Plus: A "super-powerful isotope that will finish off Kryptonians in minutes", the substance is documented in Act No. 350, May 1967: "The Secret of the Stone-Age Superman".
12. Magno-Kryptonite: Created by Truff, from the planet Pyron. "It [clings] with unbreakable force to anything that comes from Krypton" (first appeared in SPJO No. 92/1, Apr 1966: "The Man from S.C.A.R.").
14. Yellow Kryptonite: A synthetic Kryptonite made by Lex Luthor as a hoax to mentally torture Superman. Luthor claims to have a machine capable of creating hovering Kryptonite globes of various colors, including this previously unknown yellow variety. All the globes are in fact fakes, though they manage to successfully fool a Superman robot.
15. False Kryptonite: Created by Supergirl from a piece of Green Kryptonite using magic from a wishing well, it is perfectly harmless.
16. Synthetic Kryptonite: Synthetic versions of Green Kryptonite created in laboratories.
17. Mutated Kryptonite: A white card with a Kryptonian symbol on it used by the villain Zo-Mar is made from an unnamed form of mutated Kryptonite that robs any Kryptonian of his powers when he or she is very near it, but which is not otherwise harmful and has no permanent effect (DCCP No. 84, Aug 1985: "Give Me Power, Give Me Your World").