I have some inexpensive marble tiles in my upstairs bathroom that I purchased at Home Depot for $10 a box. I found that it really does scratch easily. I wish I hadn't gone with it but it was the least expensive flooring at the time.
When they put the grout in they didn't seal it. I don't know if that would have helped or not.
So what I do is use the Swiffer mop. It cleans the floor nicely and seems to be gentle enough to not put more scratches in it.