If you have a really big media chamber, like in a wet-dry, or a pond filter as Lornek8 mentioned, it would probably be fine.
For smaller media chambers, like HOB and cannister filters, it would probably be better to use finer pieces of lava rock. I've seen them in landscaping supply places and rock yards, and occasionally I'll find small bags near decorative stones and such in nurseries/home centers. Both red and black, but pebble/gravel sized. I'm currently using a bag of horticultural pumice that I found in a hydroponics supply place, that seems to work pretty well too.