• Kryptonite
  Created by internal pressures that caused Krypton's explosion, kryptonite is the ore form of kryptonium. It looks like a green glowing rock. It is very hazardous to Superman. If exposed to kryptonite, Clark will experience pain and rapidly lose his powers. If exposed for much more than an hour he would die. If suffering kryptonite posioning, Clark can recover if he gets away from the kryptonite. [The Man of Steel #1 (1986), Superman #1 (1986)]

  When Clark's birthing matrix left Krypton, a fragment of kryptonite became embedded in the tail section. Villain Lex Luthor obtained this fragment and used part of it for a ringstone, to protect himself from Superman. After being exposed to it for a year, Luthor found the radiation destroyed his hand, and was killing his body through cancer, necessitating he obtain a new cloned body.

  Note: Another villain, Mr. Mxyztptlk, a Fifth Dimensional being who can use super-science that resembles 'magic' once created red kryptonite to temporarily remove Clark's powers. Without Mr. Mxyztplk's powers, though, this 'red kryptonite' would be harmless to anyone, and is in no way connected to genuine green kryptonite.

Different Kinds of Kryptonite:

• Green Kryptonite: weakens and eventually kills super-powered Kryptonians. Usually harmless to other races, but one story in Brave and the Bold had a device used which resulted in Terrans being affected similar to Kryptonians.
• Anti-Kryptonite: similar to Green Kryptonite, but affects non-super-powered Kryptonians. This was a retcon used to explain why the non-powered Argo City residents could be killed by what seemed to be Green Kryptonite.
• X-Kryptonite: Only one chunk, it was created by Supergirl trying to find a cure for Green Kryptonite. It gives Terrans, or at least Terran cats, Kryptonian style powers for a limited time.
• Red Kryptonite: Causes a specific, odd, effect. Often involved physical transformations or mental changes. Each chunk had a different effect, and could only affect a given Kryptonian once. Effects usually wore off in 24-48 hours. Created when Green Kryptonite passed through a space cloud.
• Gold Kryptonite: Removes Kryptonians super-powers permanently. Created when Green Kryptonite passed through a different space cloud.
• White Kryptonite: Kills any plant life from any world. Yep, another space cloud.
• Blue Kryptonite: Has the same effect on Bizarro Kryptonians as Green K does on real Kryptonians. Created by the same imperfect duplicator ray that created the Bizarros.
• Jewel Kryptonite: Remnants of Krypton's Jewel Mountains, it allows Phantom Zone residents to focus their mental energy and cause explosions in the outside world.