Metallo
Note: The cyborg known as Metallo is powered by Kryptonite.
Green Kryptonite is deadly to Kryptonians, such as Superman, and other lifeforms after extended exposure. It has been known to cause cancer in humans after prolonged exposure.
Kryptonite radiation is absorbed by Kryptonians, causing blood poising, weakness and eventually death after the skin becomes green.
Green Kryptonite is beneficial to Daxamites, such as M'Onel, by protecting them from the effects of lead poisoning.
Note: After the Crisis on Infinite Earths Kryptonite was reduced to two varieties; Green, which comes from Krypton, and Red, which is man-made.
Before the Crisis, there were eight forms of Kryptonite, which are listed in order of appearance.
1. Green Kryptonite has the same color as its post-Crisis counterpart, but is only deadly to superpowered Kryptonians. Its radiation is not even cancerous to humans. {Superman Vol. 1 #61 (Dec. 1949)}
2. Red Kryptonite is Green Kryptonite which was altered by a dust cloud in space of unknown properties. Its effects are unpredictable and cause Kryptonians to either mutate physically or undergo radical personality changes. The effects last approximately 24-48 hours and the same piece of Red K rarely has an effect on the same Kryptonian more than once. {Adventure Comics #255 (Dec. 1958)}
3. Anti-Kryptonite which is green, like Kryptonite, but is only deadly to non-superpowered Kryptonians. {Action Comics #252 (May, 1959)}
4. X-Kryptonite is also green, but it is man-made and empowers non-superpowered beings with superpowers. {Action Comics #261 (Feb. 1960)}
5. Blue Kryptonite is an imperfect form of Green Kryptonite duplicated with a Bizarro Ray. It only has an effect on imperfect duplicates of superpowered Kryptonians such as Bizarro. {Superman Vol. 1 #140 (Oct. 1960)}
6. White Kryptonite is deadly to plant life, regardless of its planet of origin. {Adventure Comics #279 (Dec. 1960)}
7. Gold Kryptonite is as its name implies gold and although not deadly, permanently robs superpowered Kryptonians of their abilities. {Adventure Comics #299 (Aug. 1962)}
8. Jewel Kryptonite are gems chemically altered, preceding the destruction of Krypton, which further altered the minerals. Jewel Kryptonite empowered individuals trapped within the other dimensional Phantom Zone with telepathic powers to control events outside of the dimension. {Action Comics #310 (March, 1964)}
9. Magno Kryptonite is a man-made element which adheres magnetically to any substance from the planet Krypton. {Superman's Pal, Jimmy Olsen #92 (April, 1966)}
10. Kryptonite Plus is a super-powerful isotope which is fatal to Kryptonians in a short period of time. {Action Comics #350 (May, 1967)}
Action Comics
Adventure Comics
Adventures of Superman
JLA
Justice League America
Justice League of America
Superman Vol. 1 & 2
Superman/Batman
Superman: The Man of Steel
Superman: The Man of Tomorrow
Superman's Pal, Jimmy Olsen
Worlds Finest
Note: Although Kryptonite (possibly referred to as k-metal) was first created for an unpublished story by Jerry Siegel and Joe Shuster around 1941 the first "appearance" of Kryptonite was on the Adventures of Superman radio program on June 1943.
Unpublished
Jerry Siegel & Joe Shuster
Published
Bill Finger & Al Plastino
The chain reaction that caused Krypton's ultimate destruction is unknown, but it resulted in a new deadly radioactive element known as Kryptonite.