Iridium in nature has two stable isotopes and is not radioactive. The longest half-life of the radioactive isotopes of Iridium is 241 years and quickly disappea

Iridium in nature has two stable isotopes and is not radioactive. The longest half-life of the radioactive isotopes of Iridium is 241 years and quickly disappears over geologic timescales. Potassium is what will make stone counters radioactive as Potassium 40 has a half-life of 1.25 billion years and will release beta particles but not radon. Radon is a radioactive gas created in the decay chains of Uranium and Thorium. Stone used for counter tops will have some Uranium and Thorium, but usually at very low levels.