Hi Emma,
The thing to bear in mind when cleaning marble is to us gentle products nothing to harsh such as flash or other high alkaline products designed for lino's.
Marble is a reletively soft stone when compared to Granite. We always advise clients after performing restoration to their marble surfaces our Marble Dressing.
Marble dressing contains a nautral soap and fatty acids that work with the calcium to clean, and protect without the need to rinse off. Everytime the dressing is used it effectively gives the marble a coating providing impregnation. This isn't sufficient to call a "sealer" but for a regular maintenace product is invaluable.
Ed
www.marblemasteruk.com