Basically, avoid using all and any igneous (volcanic) rocks.
Update:
Decided to wing it and went with the shale last night. Success! No explosions–or wildfires–thus far.
too true, esp. when backpaking, etc. Luckily, this ring is on my newly bought property (i.e., no previous rings) and is on the spot where my future house will be. So I don’t even have to sacrifice any of my own land for it! (well … any land that I wouldn’t be sacrificing anyway)
Thanks, all. I’ll keep you posted re: any explosions.
Up in northern Minnesota I actively hunt for shiny shale, it’s fun to toss into the campfire and watch the little flames leap out. If you just finished some plumping work, bring along some of the copper scraps to add some color to the fire.
Exploding rocks? Damn, must have missed that in Boy Scouts. We did pretty much everything else with the campfire…