from what ive seen and heard, very hard rock becomes more manageable when you heat treat it. It depends on the temp of course, if you think about it logically you will see that when metal is heated really hot and then let cool very slowly it becomes very soft, where as if you dip it in something until it cools in a few seconds then you have just made it harder. so basically if you heat something up and cool it fast you will tighten the density of molecules thus making it harder, and vise versa is true about heating it up and allowing it to cool over about 12 hrs unlike you did previous, you will find that the molecules we not able to compact as fast, that is because when something is cold it has more molecules per inch cubed than that same substance in a hotter form. So if you are rapidly cooling a substance you will make the molecules compact tighter than if you let it cool off slowly, in any case, when you heat treat rock i believe that is what you are doing, you heat it up to about 600-800 degrees for 8-12 hrs and you let it cool off slowly, thus making it much softer. This principal is why glass shatters when you rapidly heat it and then cool it rapidly. the molecules cant handle the compression and it breaks. I hope that made sense? Good luck on whatever you choose to do, and make sure to post pics of the lovely rock!
