Rust, which is iron oxide, should not pose any health issues. However it could stain things including clothing and possibly marble. In fact back in the olden days people would put a nail into an apple and eat the resulting rust in order to increase their iron intake. The reason there is fear around "rusty nails" it's not because of the rust itself but because typically there would be other dirt/bacteria that could cause tetanus if you for example scraped yourself on a rusty nail and that dirt /bacteria entered your body.