I'm glad you asked & thought more about it- I've seen slate mentioned for possible use as a 'heat sink' for snakes, but it's risky unless used a certain way. I used to live in So. California- in the land of earthquakes- and when I first got into snakes, I used a few rocks for decoration in their homes- but after we had an earthquake (& fortunately I had no damage either to snakes or glass tanks) I totally re-thought the idea of using such things. Earthquakes can even "fling" such heavy things-I was lucky- I had a "wake up call".