My son and I get a kick out of it. For a while he was selling them on the street outside our town home, and that was absurdly lucrative for him. He has made around $200 so far. I'm pretty sure it's because he's cute. In any case, it's just a fun thing to do and experiment with, learn, and explore.

I've also thrown a bunch into an aquarium as 'river stones', because it's illegal to take them from rivers here and buying them is way too expensive. Those are just bland, small pieces of dark granite to simulate the environment the aquarium is modeled after.