Whether you call them stones, rocks, coal, or eternal ice cubes... Whether you use them in scotch, whisky (or whiskey), sake, bourbon, rum, or any other favourites...
These are the ones you're looking for.
Close to 2" round and 3/4" thick, this is a huge piece of soapstone that works as a great temperature sink. That means it will hold onto the cold for a long, long time.