We put an Italian green veined off-white marble in our steam shower. The marble is off-white in color and has green veins running through it.

Some wall marble tiles and some floor marble tiles appear to be corroding or disintegrating with normal use. Holes and crevices are appearing in the marble. In addition, when the shower marble is washed the marble seems to be crumbling away when it is sponged downed lightly. This is happening predominantly in the areas where there were green veins in the marble.

Is this normal and we should expect some crevices, cracks, and fall out to develop in natural marble that has veins with normal use?

Is there a way to prevent this?

I was always told never to use marble (especially green marble) in a wet area. Granite is a much better choice. Some people call marble a living stone. Which means it is in a process of changing on a molecular level over an extremly long period of time,(hundreds of years). In contrast, granite for all intents & purposes is done evolving. If a customer is made aware of this before installation ,then it's their problem. If they are still dead set on using a particular marble use epoxy adhesive & seal the stone. But that being said there are plenty of marble instalations using thinset with no problems. Kinda roll of the dice.