"The composition was unique. There's nothing like it on Earth, with one exception: The meteor rocks found here in Smallville. So I have fashioned my own key. It's identical in every detail." – Lionel Luthor, to Clark Kent, Exodus

The kryptonite key, identical to the Key, was created by Lionel Luthor to put into the keyhole in the cave wall inside the Kawatche Caves. He created it out of kryptonite because, as he explained to Clark Kent, the original key was made out of a metal alloy close in composition to the meteor fragments.

Clark stole the kryptonite key to destroy his spaceship and therefore the Kryptonian artificial entity programmed with the brainwaves of his biological father Jor-El. Once he placed the kryptonite key into the slot where the real key was supposed to be, a viral growth appeared on the exterior of the ship as it floated into the air. The ship then exploded, unleashing an energy wave that caused Jonathan Kent's truck to roll several times and triggered Martha Kent's miscarriage of her unborn child. The kryptonite key was destroyed along with the ship.

Kryptonite in Smallville Types Natural: Green • Red • Blue • Gold kryptonite • Processed: Black • Silver • Gemstone • Clear kryptonite Effects Meteor infection • Psychosis • Meteor freaks Objects Bullet • Cage • Handcuffs • Heart • Key • Ring • Necklace • Victory ring Other Krypton • Meteor showers (1989, 2005) • Lead (box) • Appearances of Green K (usages)