I have a rust stain on the baseboards of white carrera usually I use rust out and diatamcious earth and it will do the job. Done this eight times and nothing.  Ifyou have outher poultices please confirm.  Im thinking this is not rust

Dayron Padilla
Perfect Marble Restoration & Janitorial Services, inc.
305.970.0213
www.perfectmarblefloors.com