Steve,
Here is how Patrick cooks his rock.
Heating makes a lot of difference in some rocks. Dry the rocks in a taster oven at 250 degrees for a few days. Then heat to 350 degrees for a few hours and then let it cool down. Take a few flakes off to see if it's glossier than before. Discard cracked pieces. If they all crack, the rock cannot be heat treated. If the rock is a little glossy, then heat at 450 degrees for a few hours then let it cool down. Takes a few flakes off. If it's glossy and not too brittle, you're good to go. If it cracks or doesn't get really glossy, then you probably don't want to heat treat at 450 degrees. You can experiment with higher heat, but I recommend only heating to 350 or 450 and using the rock that responds well at these temperatures.
This only a suggestion. I'm not an expert in heat treating, by any means.