It's probably an alkali burn from lime in/on the rock.
If you got that from radiation, you're going to be dead in a week.
Half life for the most stable isotope of iridium is 241 years. All the other isotopes of iridium are rated in days, minutes, seconds, and milliseconds. I seriously doubt you have any iridium other than a trace amount, and not enough to cause any radiation burn.
Hmmm....Alkali/radiation burn....Might be cesium. You might have a chunk of a satellite reactor and one hell of a mess on your hands!!!