Trivia 012: The Most Dangerous Marshmallows

Well, it’s starting to feel like spring has sprung where I live. It finally got above 70 degrees yesterday. We are currently preparing for the large spring/summer influx of visitors to our state parks. And so, as the weather starts warming and people start going outside more, I figured this would be a good time to share a tip to anyone who’s planning on going camping this season: Don’t put river rocks in your campfire.

Although they are nice and smooth, which makes them convenient to cook on, putting river rocks in a campfire can be quite dangerous. They often contain small pockets of water trapped inside the crystalline structure of the stone. When this water gets heated, it can turn into steam. The superheated steam expands rapidly, and can cause the stone to explode. Depending on the type of stone and amount of water, this could simply mean it breaks in half, but it could also turn it into a veritable grenade. The last thing you want while roasting marshmallows is to have to suddenly dodge rock shrapnel.

Now, all stones contain some amount of water. However some are more dangerous than others. River rocks are particularly bad because, well, they’re from a river. However, you should also look out for rocks that are especially porous. Examples of these include limestone, sandstone, pumice, and shale. Also watch out for conglomerates – these are rocks which are made of other kinds of rocks stuck together by sedimentation. If you want to put rocks in your fire, the best ones to look for are granite and slate. These are very dense, nonporous rocks which probably won’t have much water trapped in them. However, if they are particularly rounded, they may come from a riverbed, so you might want to avoid them. This same advice goes if you are making a fire pit at home.

This was a pretty short trivia today, so here’s a bonus. Since prehistoric times, humans have used a technique called “fire-setting” to help them mine. By lighting a fire next to a rock, they would get it extremely hot. Then, by dousing the rock quickly with cold water, it would fracture. This is because the sudden thermal contraction would put too much stress on the rock. This technique was actually still in use in some places well into the 20th century, as wood was easier to come by than explosives.


If you know anyone who would like to receive these, please have them send an email to [email protected] And if you no longer plan to go camping, let me know and I can take you off the list.

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