Tile as substrate for leopard gecko

I am going use tile or slate or something like that as substrate. I am going to also use the zoo med under tank heater as my only heat source. It comes with these tiny knobs to stick on the bottom corners of the tank to elevate it.By using a heavy substrate, would it break the tank?

The key with glass tanks is to keep them level and the little feet should still keep the tank pretty level. However, tile is a paltry amount of weight when compared to water. Making sure you have a thermostat to keep the heat matt from getting overly hot is more important to avoiding cracks.