I don't like watered down drinks, so I've been known to use reusable ice cubes rather than plain frozen water. When I was looking for a new set, Mocha's Nordic Rocks caught my eye. These reusable ice cubes are durable, nontoxic--and made out of rock! They come in sets of 10. Each rock is 22 millimeters cubed. To use the Nordic Rock cubes, you just place them in the freezer for about an hour. You'll probably need two or three for a glass, but Nordic Rocks give off the cold slowly.
Nordic Rock is mined from "ancient Swedish pollution-free base rock," according to Mocha. Though the Web site does not list exactly what kind of stone is used for Nordic Rock, it seems likely that it is calcium carbonate--a type of rock used in aquariums because it won't poison anything. As long as it is clean, placing a cold rock in your drink is safe. I wouldn't recommend trying to chew these ice cubes, though.
Keeping your Nordic Rock clean is easy: all you have to do is rinse the stones and put them back in their leather storage pouch. The pouch comes with Mocha's set of Nordic Rock.