Can’t be produced under the yellow sun of earth. Only exists under the red sun of Krypton (not to be confused with the Noble Gas, Krypton, which isn’t named “Krypton” on Krypton.)
Well, before man-made global warming, our sun must have been red because I remember a Superman comic book from my youth where kryptonite was used to damage the super dude here on Erf.
Includes a dark matter component explaining Krypton’s high gravitation and density?