You're may have to call a natural stone restoration service and have the floor ground and polished, depending on how far gone they are. Marble, like all natural stone flooring, wears and loses its shine as tiny scratches in the marble's surface dull it's finish. I have natural terrazzo floors in my house, which contain marble and granite embedded within a cement base. To bring back the shine on these 50 year old floors, they had to be wet ground with a diamond pad, and then polished. It was worth every penny. The floors came out beautiful. The nice thing is that the guy who did the floors said that if you take care of them, it really never has to be done again. It helps to take your shoes off before walking on them, too, because you track in abrasive materials on shoes from outside that can mar the finish on the floors. So far, after a year, they still look new.
Natural stone is not indestructable, it has a finish that can be penetrated by cleaning solvents, and that finish can be destroyed and dulled. Never use anything with an acid base, like vinegar or lemon, on marble, it will penetrate its finish and destroy it. All natural cleaners like Simple Green are the way to go....just a small amount on a properly finished floor is all you need (1 tbsp/gallon of water). You'll be amazed at how the floors stay clean with just sweeping or vacuuming once they're refinished.
I hope that helps somewhat! And shop around for services...I fouond the prices varied dramatically for the exact same service....from $4 a sq foot down to $1.60 a sq ft. I went with the $1.60 sevice, and they did a brilliant job.
