Marble Disease? What is causing this?

[missbossy]

The green granite tiles in my bathroom are showing signs of corrosion. In a few spots (not exposed to water) the granite has become chalky and pitted. The stone seams to be eaten into a white powder. The corrosion appears to spread from one area to another like a disease.

If I don't wipe the area where the corrosion appears, a dusty moss will grow - it looks like some kind of fungus. There is no smell.

Any idea what this is and what I need to do to stop it? It's doing irreparable damage to some of the tiles.

[rob w]

It sounds like your granite is actually either reconstituted stone or a mixed stone that has a high level of calcite in it.
To check do a "lemon test”

[missbossy]

Thanks - I'll try it.