Glad I could help! You may even want to just soak them in water that was boiling hot (like you would do in a tub with a large piece of driftwood) to kill everything, because it won't heat the inside of the rocks enough to risk then exploding.
You should also do the vinegar test to make sure they won't alter your tanks pH
Uh oh...how do I do the vinegar test?! I have normal clear vinegar, will that work? I don't want to shock my fish with ph crash/spike!! Glad u mentioned that, hadn't thought of it :-/