Here is some info on boiling rocks. This info was posted by Fish-for-all in the freshwater fish and aquariums section of FishForum.
DO NOT BOIL ROCKS!!!!!!!!!!!!!
As many of you are aware a lot of people use rocs in their aquariums. This is fine but there aresome things to know before using them. The first is to make sure they are inert. This is done by putting them in vinegar and seeing if they bubble. If they do they will change your tank parameters, most likely your GH but can change yur KH and pH drastically. Now this is wanted sometimes but as a general rule if it fizzes you don;t want to use it. The second is the best way to disenfect a rock is to use alcohol or to pour boiling over it.
NEVER BOIL A ROCK!
Regardless of what it is made of or the type, if there is any water in the rock it can explode and destroy your kitchen or even worse, YOU!
If you want to change your pH with rocks, make sure they are clean and the rights ones before using them.
If anyone has any more ideas for disinfecting rocks for the aquarium please post them. Also, any information on rocks that are specifically used for changing the chemistry of your aquarium for specific fish would be very useful for many members.