Marblt Tiles

I had marble tiles put down about a month ago from the kitchen into the hall. Over the last few days I've noticed some "chips" appearing in them. Its like a small lump has come away from a few tiles. The other half reckons its because they are natural stone and from walking on them certain parts are softer then others and therfore have broken away.

Anyone ever had this happen before - is it something I should be concerned about or is it simply a case of the tiles settling?

Cheers in advance for any advice.