Poor granite. This species suffered a near 100% failure rate. I’ve been told by a geology professor that water can infiltrate the interstitial spaces between the relatively-large quartz, feldspar and mica crystals and expand the rock when heated. To it’s credit, granite never sent shrapnel flying when it cracked.
Quartzite fared a little better, being smaller-grained and more homogenous throughout it’s structure. About 50% of these survived. I will note that when quartzite cracked, it sometimes exploded (but shards never traveled more than a foot or so away from the wooden bowl.
And the winner is . . . .
Basalt out-performed the other species of rock by far. Only about 5% of these cracked with use. A few years later, I still use these particular pieces of basalt. They show no signs of giving out. Incidentally, one can purchase smooth basalt cobbles in fancy home/yard furnishing stores.
Visit Storm's website at www.stoneageskills.com.
Storm (1969 - 2008)
Storm immersed himself into the wellspring of adventure and the experience of the Stone Age. Thank you, Storm, for sharing your heartfelt enthusiasm of the wilderness and skills of the past through your engaging articles. You will be sorely missed.
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