Granite Cracking

I am a foodservice design consultant, several of our projects have Granite (http://tanbrown.org) Counter (http://GialloFiorito.com) tops that have developed cracks, we did not specify the Counter (http://GialloFiorito.com) s (Granite (http://tanbrown.org) ).
I am trying to support my clients need to understand (http://maplered.com) the following:
Why did the cracks appear? And What if anything can be done to repair or prevent if Counter (http://GialloFiorito.com) s are replaced.
Note that the Counter (http://GialloFiorito.com) s are ¾” dark Granite (http://tanbrown.org) , with cut outs that range from 18?X 9?ovals to 20?X 12?rectangular opens some opening are with in 3??4 ?of each other and (http://maplered.com) 4??6?of the edge, the Granite (http://tanbrown.org) Slabs (http://www.VerdeUbatuba.com) are 39?wide X 4?to 8?long.   The cracks predominately occur at the corners of the cut outs. The cut outs have hot wells seated in them that transfer heat into the Granite (http://tanbrown.org) (average Stone (http://g603.net) temperature is 180 to 250 degrees, there are also heat lamps that are mounted above the Stone (http://g603.net) (15??18? they added heat to the Stone (http://g603.net) , with in the temp. range stated above. Most involved with the project think the heat is the problem, however I am of the understand (http://maplered.com) ing that the temp. is not sufficient to cause the Stone (http://g603.net) crack. There are downward pressures that also come into play as well.
Can you shed any light on this issue?