an icepick through the keyhole

That's quite a stretch. I haven't followed Superman lately, but my understanding is that the explosion of Krypton turned all its rock radioactive in a way which is deadly only to surviving Kryptonians. The piece in Superman Returns may have been sodium lithium boron silicate hydroxide by chance, but Kryptonian quartz or granite would also have become Kryptonite.

It does do the writers credit that they came up with a formula that's physically possible, though.