Originally Posted by okapizebra
Do NOT boil rocks. Some can have air trapped inside them and boiling them can cause them to explode. A good scrubbing and rinsing should be enough to properly clean them. If you want to make sure the rock with not mess with your pH, put a few drops of vinegar on the rock. If it bubbles, it will change your pH. If not, you should be fine.
I knew there was a reason not to boil rocks, I just couldn't figure it out. Thanks Okapizebra.
I usually just scrub them really good and soak them for awhile. Never had any trouble.