Marble tile will crack when it is cut due to the natural fault lines that are in marble. Imagine these fault lines are folds in a sheet of paper. If you try and tear the paper past the fold, then the paper will try and tear up that line as it has the least resistance.
The same principle applies to the fault lines in marble. There is less resistance against the cut on a fault line than there is on the rest of the marble slab. The best tool to use to minimize the cracking of your marble tile is a wet saw. Apply minimal pressure for the best results.