Part 4 of "The Colors Out of Space"

Blue Kryptonite. This is Bizarro Kryptonite. Its infrequent history begins in Superman #140's three-part "Son of Bizarro" novel. To prevent an angry Bizarro army's invasion of Earth, Superman uses Luthor's confiscated Duplicating Ray on Green K, correctly surmising that the product will be just a dangerous to Bizarros as the real stuff is to him. The resulting Blue K stockpile scares off the Bizarros, the only casualty being the story's heavy, a Bizarro Supergirl.
The only other appearance of Blue K is in Superman #423 when Bizarro No. 1 destroys his world and then uses Blue K to kill himself after wiping a city blockful of Metropolis citizens.


Jewel Kryptonite, aka Kryptonite Six. Action #310 tells how Lori Lemaris and the merfolk of Atlantis are stricken with a strange spotted plague. Jax-Ur of the Phantom Zone talks Superman into a 24-hour parole, saying he can cure the Atlanteans. Their quest take Jax-Ur and Superman into Krypton's past, where the criminal drugs Superman long enough to sneak to the nearby Jewel Mountains and treat a huge gem there with a strange ray. "Because my device has transmuted its elements, this mineral will be transformed into a new form of Kryptonite with incredible powers!"
After their return to Earth and the curing of the Atlanteans, Jax-Ur returns to the Zone, where his plot thickens. After Superman encounters the Jewel K that has now drifted to Earth, things start blowing up whenever Superman nears them. To his horror, Superman concludes that "Jewel K may be causing me to detonate any explosive material that I approach!"
Little does he suspect that the explosions of all those oil tanks, sea mines, and rockets have been in fact caused by the Phantom Zoners. "That chunk of Jewel K in orbit magnifies our mental commands and converts them into energy beams which detonate any explosive material we desire." Yes, it was all a scheme to blackmail Superman into letting them out of the Zone. But the Man of Steel tumbles to their scheme and throws the orbiting chunk into the sun. As he tells Supergirl, "That was a close call! The power of Jewel Kryptonite might have helped the Phantom Zone criminals take over the Earth!" If only Superman had also destroyed the first, tiny pieces he'd encountered! 18 years later, in 1982, some Phantom Zoners track down that small piece, hurled into space by Superman long ago. A few, led by General Zod, escape the Zone. They then confuse Superman by not fighting him but asking for his help against the Vrangs, an alien race which once enslaved Krypton (as earlier told in Superman #176). After a long battle (Action #548-549), the Vrangs are finished and the Zoners then turn on Superman. But he has been ready for this, and manages to return them to the Zone, finishing the saga of Jewel K by pulverizing the last fragment.

X-Kryptonite. Superman isn’t the only one looking for a Kryptonite antidote. Action #261 tells how Supergirl nabs a piece of Green K. In the sort of continuity error frequent in Supergirl stories, she discovers that "friction with the air has reduced it to about the size of a marble!" (Experts like you and me know that Green K does not burn up in the atmosphere, remember?) She tries various chemicals on the deadly fragment to no avail; so she super-tosses it with a pair of lead tongs into some nearby woods.
That night, a cute cat Linda has named Streaky comes across the Kryptonite fragment. Soon "he is absorbing mysterious rays from X-Kryptonite, something new under the sun, accidentally created by Linda when she had experimented with the chemicals!" After surprising Linda with his newfound powers, Streaky soon loses them again as the X-K wears off.
In future issues Streaky repeatedly acquires his on-again/off-again powers until, eventually, they seem to stick, enabling him to join the 30th century's Legion of Super Pets.
Since not even Streaky ever figured out the source of his powers, that little piece of X-Kryptonite may still be out there, waiting to give someone super-powers. Say, do you suppose President Reagan had come across the stuff just before Hinckley took a pop at him with his pistol?