Actually I think it's a gas that you can't see. I don't think it is poisonous. If you freeze it you might be able to make it look like the kryptonite on Smallville.
Kryptonite is a rock. It comes from the fictitious Superman comic strip and movies. Krypton is an element on the periodic table. It is a gas. See the related link for more information.
green kryptonite gas
Kryptonite.
Silver kryptonite.
A couple of possibilities in the rock genre: 3 Doors Down ('Kryptonite') and The Spin Doctors ('Pocket Full of Kryptonite').
No. Kryptonite is a nobel gas, and doesn't react with any other elements.
Radiation
Kryptonite. Its a rock from his home planet of Krypton. :]
All of the colors of Kryptonite would include Green Kryptonite, Red Kryptonite, Black Kryptonite, Blue Kryptonite, Gold Kryptonite, White Kryptonite, Yellow Kryptonite, Silver Kryptonite, Pink Kryptonite and Purple Kryptonite.
Superman doesn't exactly have allergies, but the space rock "kryptonite" weakens his powers.
Kryptonite is a rock from a fictitious Superman story. But there is a mineral found in 2007 in siberia that has the exact same elements as the fictional stuff. all except flouride the element is nicknamed kryptonite but cannot be called that for the element of krypton so it is named jadarite for the town nearest to where it was found.
The song "Kryptonite" was written by Brad Arnold, Matt Roberts and Todd Harrell. It was published in the year 2000. The genre of this song is alternative rock.
Kryptonite is Superman's weakness.