You would want something that is made for or says "safe to use on" marble and stone. John Koessler over on the John Bridge forum (a tiler and also a rep for STT products) recommended STT's cleaners EZCLN and HDCLN for my marble, stone and tile--I'd called him to discuss and order their sealer and we discussed cleaners as well (I'd run out of SCI's Marbalex, which we had been using, and can't find it locally any more--if I had to mail order something anyway, it was worth trying the STT cleaners since I was already ordering from him). My Thassos mosaic in the MB is in the process of being installed, so I haven't used anything on it yet! I can say, that I tried the HDCLN on my discolored grout/glass tile backsplash in my kitchen (just above the vent trim at the back of the range), and it worked very well--faster and easier than using OxyClean. I had called STT directly a couple of months ago while I was doing my HW/research on sealers (hated the stuff we'd used in the guest-bath), and spoke with Steven, the owner of STT. Really nice guy (as is John, BTW), and passionate about their products; their effectiveness and safety, etc. Patient, too! Both men have answered my numerous questions and gave me tons of info about the products, their uses, and any other marble and stone questions I had. I'll let you know how well the cleaner(s) work on the marble when I get to start using the MB!

Been used for centuries. Use non-acidic cleaners like MB Stone Care. Take the easy precautions (true for any shower surface) and ensure proper ventilation (and use it), quick squeegee and wipe with micro-fiber towel after use. Of course the most important factor for longevity is not the tile or stone on the surface, but how the shower was built (methods and materials). And yes, pay attention to the quality of the marble. It does make a difference. Like anything else, you will pay more for quality.

Hate to say it, but I'd use a small hex in same carrara marble, which is probably what you have on the floor of the showers?. You can't mix in another veined anything..... and any solid light or dark floor will show hair, and dust. The smaller the tile, the more patterning ....veining and busyness will result.. A better disguise. Grout in a pale gray/ Keep the Swiffer handy. Truth is most baths need an every day wipe up and a serious once a week cleaning. No tile will allow the escape from maintenance.

so the large beige-ish tile is going on the floor and that patterned tile is on the shower wall? can you post a pic of the room? does that large tile come in a 2x2 or 3x3 size? it should. use that. u said it looks busy, but I don't see how. it's a solid look tile. same premise they've done here. used a smaller tile in the same make as the floor introducing any other type of mosaic will look busier. if your large floor tile is a matte finish, it could be cut and used on the shower floor. maybe have it cut in thinner, rectangular strips. they've done it here in the shower