Kryptonite?

Scientists announced that they discovered kryptonite!

A mineral found by geologists in Serbia shares virtually the same chemical composition as the fictional kryptonite from outer space, used by the superhero's nemesis Lex Luthor to weaken him in the film "Superman Returns."

{...} Stanley, who revealed the identity of the mysterious new mineral, discovered the match after searching the Internet for its chemical formula — sodium lithium boron silicate hydroxide.

"I was amazed to discover that same scientific name written on a case of rock containing kryptonite stolen by Lex Luther from a museum in the film 'Superman Returns,'" he said.

But what about the "tar" in the artificial kryptonite in Superman III?

Of course, it isn't kryptonite unless it is green (or red, white, gold, or blue) and glows. More importantly, it can't be kryptonite unless it comes from Krypton.

The comic books were always a bit vague about what kryptonite really was. It usually came to earth looking like a chunk of rock but it could be melted and made into other objects like metal. It was treated as an element. Possibly, just as uranium will become plutonium when exposed to the right radiation, most other solids will become kryptonite when properly treated. Additional treatments cause it to change into red, white or gold varieties. Blue kryptonite is an imperfect copy of green and will kill Bizarros.

As you would expect from something glowing, kryptonite was radioactive although it did not bother terrestrial life (except for the white form which kills plants). It could be harnessed as a power source which Metallo did.

Originally the explosion of Krypton transformed all of the planet's fragments into kryptonite. The young Kal-el's spaceship opened a wormhole to Earth and a significant amount of kryptonite followed through this.

Besides killing Superman and powering cyborgs, kryptonite had one other interesting use - it was not affected by the heat of entering Earth's atmosphere. It might have made a good coating for the space shuttle except, as soon as someone did that the shuttle would have failed (with Lois aboard) and Superman would have to rescue a craft that could kill him.

Kryptonite could also protect an inhabitant of Daxam from lead poisoning. In the 30th century, Mon-el had to take kryptonite pills regularly to stay healthy.

Kryptonite could also impregnate a living being. One such was the Kryptonite Kid who could not only kill Superboy with a touch but could also transform anything he touched into kryptonite.

When Superman was re-created by John Byrne in the 1980s the source of kryptonite was changed around a bit. Centuries before terrorists had tried to destroy the planet. They were stopped but not before they started a process that converted much of the planet into kryptonite and caused it to explode.

Originally kryptonite could kill Superman but it did not remove his invulnerability. A kryptonite bullet would bounce off of him the same as a lead one. The revised Superman could be shot with a kryptonite bullet (probably because his impenetrable skin was replaced with a force field which failed in the presence of kryptonite). Also, long-term exposure to kryptonite turned out to be fatal to humans as Luther found out after wearing a kryptonite ring for years.