About a week ago I went camping with some friends. We’ve been to Alsace in France if that is to any importance to my following question. We build a stone oven to make some delicious “Tartes flambées” (a bit like Pizza). In order for the oven to be heated we made a campfire around and under it (the groundstone was a little elevated). Until now everything was as usual ,we’ve built these kind of ovens many times.
Soon after the fire was lit we started to hear loud bangs from the oven. It is usual to hear light cracks or even bangs from stones when you heat them like that, but these sound were really loud, like gunshots. We continued to fire the oven because we thought there were some big tensions in one of the stones and everything would be okay when these tensions were gone. But thing got worse, the groundstone would start shooting little stones all over the place. Sometimes bigger pieces of the stone fell into the embers of the fire and these pieces would start exploding at about one bang a second! We saw marble-sized pieces hit or tent which was situated about 8 metres/yards away from the fireplace. So we let the fire go out when the ground stone completely broke apart and had and evening without a warm meal or a campfire to sit around. Fortunately none of us got injured.
What kind of stone was that that? I have seen a lot of fireplaces (with stones around them) and never seen such a spectacle. Neither has one of my friends, most of them rather experienced “outdoor guys”.
The stone has a light redish colour and the surface structure is rather uneven (not like e.g. flintstone which has a very smooth surface).