Natural marble does some fun and exciting things. One of them is 'etch'. Etching is when an acid (aka...water) hits the surface and reduces the gloss level. It also stains (that's when COLOUR is left behind...like from a cleaning product, wine, etc).

Marble can be sealed before, during and then after install (yah some marbles x3 applications of sealant). Sealant prevents staining...but etching (change in gloss....like what you are showing here) will continue.

The way a tiling pro would 'determine' if the issue is 'unreasonable' (ei. quality of tile OR quality of installation) is by standing roughly 5 ft away from the problem. If it is visible from a standing position (5-10ft away) and WITHOUT having to 'turn his/her head at an angle, at a certain time of the day...during the Lunar cycle....etc'.

Etching (we call it water etching...for obvious reasons) is part and parcel of marble. So long as the rest of the install is appropriate and the shower drains properly, there isn't much you can do about it.

The one thing you CAN do: Towel dry the tiles every time your shower is used. Do not let the water sit on it. This will prevent hard water stains from occurring as well.

This isn’t on the shower floor. It’s on the bathroom floor

Same issue. Different place to stand. Go ahead and open up the left over boxes of tile and see if you can find the same issue.

Contact the company that sold it to find out if it is 'pre sealed'. Then contact the installer to see if s/he sealed the marble and with what. Marble requires yearly maintenance. Sealants need to be reapplied from time to time. You will want to know the name of the sealer so that you can get 'more of the same' for your next application = 6-10 months from now.

I'm sorry if no one informed you of marble's quirks. It is stunning. It is a 'living' finish (that means it changes every day...all day...you will see new and different things happen every so often...like rust stains coming out...etc). And it is perfectly imperfect.

Go ahead and see if you can 'buff' out those little etches. Use the softest fabric you can and go at it over 2-3 tiles. After sweating for a few minutes over those few tiles you then compare them to the other ones with the etching. Does the buffing help? If so, you know you need to buff the surface of the tiles. And keep the buffer handy. Marble etches (loss of gloss) when it is exposed to water. That means you can expect to see this happen over and over again.

Will do. What agent should I use to buff?

Did you use a cleaning solution when you tried "scrubbing it"?

If you have any males using this bathroom ... any drips will permanently etch the tile.

It's really beautiful and I doubt anyone but you will notice the water spotting. I know that's no comfort when you don't like how it looks, but when I looked at your pic it took me a while to figure out what your concern was, as it looks so gorgeous with that black grout.

Marble etches. Etching is really permanent. If you can't stand the etching and the changing finish of the marble, then you need to put down porcelain, not marble. I have marble and expect it to etch. In fact, I honed the surface of my tiles before having them laid down.