If you've done any homework at all on how to properly care for your natural stone, one of the first things you probably learned was that certain types of stone (marble, limestone, onyx, among others) are susceptible to damage from acidic substances.
Flaking (also called spalling) in natural stone is generally an indicator of sub-florescence, a condition in which mineral salts are carried into the stone by moisture and accumulate beneath the stone’s surface. This article will inform you about this condition.
If you have mysterious odors that you can't quite identify the source, it just might be coming from your grout lines. Professional cleaning followed by sealing will resolve this issue.