Is it safe for my chinchilla to do this?

We live in an apartment with exposed brick walls, every time i let my chin out to play he shoots straight for the brick and chews on it. i know they like to chew on things and it is healthy for them to chew on untreated wood, but is it healthy for them to chew on the brick? i wouldn't think so, but i don't know if it will cause them problems, it doesn't seem to have caused any so far, but im still a little worried. if it is unhealthy how do i get him to stop? can you train a chin to know when he is doing something "bad"?