In the process of grinding a marble floor. I am getting a lot of the corners of the marble cracking. Why is this happening?

The marble tile was most likely improperly installed. Before you grind a floor you should sound the floor by tapping on each tile with a broom handle. If you hear a hollow thud sound then there is a strong chance that the tile has no setting material in that area and it will be suspectable to cracking. There is very little that can be done to correct this problem.

TIP There are now methods of injecting an epoxy resin in these areas by drilling small holes in the grout joints and injecting an epoxy resin into the hollow voids. This is a labor intensive procedure that should be performed by skilled labor familiar with this procedure.