To my understanding, kryptonite is a rock that is from the planet Krypton. Superman is also from planet Krypton. Yet somehow kryptonite weakens Superman and can even kill him.
How does this work? Why exactly does kryptonite hurt him? Isn't his entire home planet made of kryptonite?
Not only does it prevent the further absorption of solar energy, it displaces, painfully, said solar energy with kryptonite radiation causing the immediate loss of a Kryptonian's superhuman abilities within seconds and can, depending on the purity and exposure length, lead to the death of a Kryptonian by a form of "radiation poisoning".
A nice analogy (promoted by AncientSwordRage) in a fashion similar to "carbon monoxide poisoning" where carbon monoxide molecules are being taken up by blood's hemoglobin instead of the normal Oxygen molecules. The CO is displacing the O2 molecules but not providing any oxygen necessary for life. With sufficient displacement of O2 molecules a person can die.
DC has made no official "scientific" rationalization as to HOW Kryptonite works. Over the decades, we are given a variety of reasons it works, but just vague enough we cannot be exact on the process within his cellular activity.
Kryptonite's origins vary but most describe their creation at the core of the planet Krypton and were in some continuities responsible for the explosion and destruction of that world. Many pieces arrive on Earth because they traveled near the space-ship Jor-El sent baby Kal-El to Earth in. Other pieces were thought to arrive later.
Most depictions indicate it was only the core of the planet which was comprised of Kryptonite, though some of the earlier ones indicated any piece of Krypton that came to Earth was considered Kryptonite.
Kryptonite's origins vary depending on the continuity from which it appears in. In the Silver Age, kryptonite came in a variety of colors and each color had specific affects which were caused by exposures to different radiations, natural phenomena or scientific experimentation.
In almost all known continuities it is Green Kryptonite which has proven to be lethal to Kryptonians who have been exposed to its radiation. Green Kryptonite was lethal to any Kryptonian from the same universe the Kryptonite was derived from.
Several of Superman's foes use Kryptonite as part of their arsenal of weapons including Lex Luthor, who wore a ring with a piece of Kryptonite embedded in the ring. Luthor wore this ring until it gave him cancer.
Said ring was recovered by Superman and given to Batman, as a part of a contingency plan to "stop" Superman should he ever be mind-controlled or have his free will compromised.
Metallo has a robotic body whose powerplant uses a hunk of Kryptonite as its power sources. Brainiac was also fond of using Kryptonite in many of his schemes including creating a body covered with the material.
More modern depictions of Kryptonite only show small amounts of Green Kryptonite on Earth, but some advanced science has been able to duplicate the signature radiation making it capable of being used as a weapon against Superman.
As an aside, the Green Lantern's ring is also able to replicate the signature of a piece of Green Kryptonite potentially making them capable of defeating Superman, if necessary.
No, Krypton was not made of Kryptonite - at least, not initially.
Kryptonite is a radioactive mineral from Krypton. The most common form is Green Kryptonite, but it comes in other forms, including Red Kryptonite, which has unusual temporary effects on Kryptonians, but only works once, and Gold Kryptonite, which would permanently remove Superman's powers.
Depending on the era, either Kryptonite was created by the explosion of Krypton, or it was found in the core of Krypton, and was released when the planet exploded.
The radiation from Green Kryptonite is poisonous to Kryptonians, causing weakness (removal of super-powers) and effects similar to radiation poisoning in humans. It's not quite the same, because Kryptonians recover very quickly when the radiation source is removed.
Reference information here: http://smallville.wikia.com/wiki/Kryptonite
You're Earthling, but lots of Earth-based rocks can hurt you (Radioactive ores).
Second, Kryptonite (green one) wasn't found on Krypton. It was produced during explosion of Krypton.
Superman (and, Kryptonians) has superpowers on Earth because of our yellow Sun (Krypton's Sun was red). Kryptonite blocks that ability. Also, its radiation is poisonous to Kryptonians which can kill them (although, I have read comics in which Superman had developed some immunity against green Kryptonite).
There are various types of kryptonite, and they all have varying effects on Superman. Each type of kryptonite contains/emits different kinds of radiation. I would think this is similar to the different radioactive elements contained within the planet Earth (plutonium, uranium, cesium, etc.)
We've been told in the comic books that green kryptonite, which is deadly to Superman, comes from the core of the planet Krypton. Likewise, the core of the planet Earth is radioactive and would kill any of us.
It stands to reason that if we were to end up on another planet, with a red sun, and if our cells were to consume the red sun radiation, giving us superpowers, that pieces of the Earth's core would still kill us - even if other beings on that planet were immune to it.
BTW - nothing in the comic books or movies or television shows says that kryptonite is exactly safe for humans either. But one would imagine that the rarity of the material generally keeps it from effecting us. If they were to find a vast kryptonite mine in Starling City or Gotham, my bet is that there would probably be a pretty large "cancer cluster" among the nearby humans.
In Superman the Animated series the idea is the minerals and superman's biology contain similar elements, as such his body chemistry is easily more suited to absorbing the radiation but his powers are always in state of trying to fight it off but failing. However I also believe it's psychosomatic like expecting pain like touching something cold you think will be hot. He simply never feels pain or discomfort.....seldom, so the feeling must be overwhelming. Imagine if you were 30 years old and never had a cut or stubbed your toe or ever get an inoculation or ever felt pain in any way. How do you think you'd react if after 30 years of never even knowing what pain was you accidentally cut yourself?
