Unfortunately, rust stains are typically the most difficult to remove from marble or any stone, so don’t expect quick (or perfect) results. In fact I considered most rust stains permanent, here’s why
With rust the cause of the rust problem often is the greatest factor that determines if it can be removed. The answer to the “what is the cause” questions changes the nature of the problem and the result.
Is the rust stain from a metal object left on the marble?
If so, rust stains from an object left on the marble are typically easier to deal with. They tend to be recent, and more surface stains. Of course, you will know that the stain is from an object if it has a very distinct shape and is red-brown in color.
Is the marble in a wet environment like a shower?
We love our White Carrara marble showers in Pittsburgh. But this could be a problem if the shower was installed wrong or is starting to have leaks. Why?
Some white marbles… notably Carrara marble… contain iron deposits. If the marble is somehow absorbing water (usually from unexposed sides.. not the surface), the iron will rust and bleed through the marble to the surface. Or the iron could already be on the surface and oxidizing.
Typically rust spots from such a problem are through the whole stone and look like yellow-brown stains rather than red-brown with a distinct shape.
Iron deposit rust stains result from flood, plumbing leak, grout cracks or poor installation.
On flooring, water can seep up through cracks in the foundation and poor tile setting or voids in grout in showers allows water to get trapped underneath tile.
Or, it could be an isolated leak in plumbing.
Of course, if this is the case… you have a much bigger problem. The staining will continue to occur as long as the marble is exposed to moisture.
You’re only solution then is to live with the stain or to rip it out, fix the leak or otherwise seal the source of moisture and re-install.