It is easy to spot a rust stain on marble. It shows up as a perfect circle under the shaving cream can or the striped image of a screw. The Marble Institute of America says that rust is one of the most difficult stains to remove. It offers the following instructions for removing or at least improving a rust stain. If scrubbing with one of the safe nonabrasive scrubbers has not removed your rust stain, don't resort to steel wool. Try this.

1
Mix liquid rust remover with diatomaceous earth to form a thick paste.

2
Wet marble first before cleaning.Wet the marble with distilled water.

3
Cover the stained area with a layer of the mixture one quarter to one half inch thick. Extend the mixture at least an inch beyond the stained area.

4
Cover this with plastic wrap and tape down the edges.

5
Allow to dry for one or two days.

6
Remove the stain-removing mixture, rinse with distilled water and dry with a soft cloth.