One year we had to build a fresh fire-pit at elk camp (some wahoo took all the stones from our old, well established one). All there was available at the time was fractured basalt that had been covered in early snow. That stuff popped and hissed at us for days. We had to keep our distance or else get shrapneled out, and even at 20 feet we were still getting stung by little bits and pieces. Lesson learned.