Despite its name, Kryptonite is not made of the element Krypton. There are a number of versions of Kryptonite over the seven decades Superman has existed, but no matter when it is described, it is almost never composed entirely of the noble gas, Krypton. ... Krypton is inert for most practical purposes.

Is Kryptonite part of Krypton?

Kryptonite, that glowing green rock from the core of Krypton, is one of Superman's few Achilles' heels. Time and again it is a plot device to make the hero human.

Which Kryptonian is immune to Kryptonite?

Surprisingly, however, Superman once accidentally discovered a relatively simple way to render himself immune to all forms of Kryptonite.