Fire and exploding rocks.

[Darryl of Sussex]

How did you find out which rocks not to use around a fire? Is there a specific type and if so, what causes it to explode when heated in fire?
the simple answer has to be if in doubt, don’t but i’d still like to understand more about which rocks to use and which to avoid.

Many thanks,

Darryl

 

[crosslandkelly]

https://www.hunker.com/12397976/rocks-that-explode-around-fire-pits

 

[Janne]

Any rocks that absorb water can explode. Granit, gneiss and similar no.

 

[Robson Valley]

Soft rock here which has the look and feel of being porous. They get wet inside = steam.
Really hard rock survived the grinding action under the glaciers of the ice age.
Very smooth surfaces, very finely granular structure. Damn difficult to break with any other rock.
I'd be picking grapefruit sized and bigger out of river bottoms at low water (autumn when it freezes again, up top.)

I confess that we usually find well-used fire pit rock rings in all the best(?) wild camp sites and many other places.
Those rocks have been fire tested. Make a fire, set up camp, sit and eat.
Broken ones are a sign of sudden cooling when water is poured into a fire to put it out.

Big flat stones are a prize to set pots and pans on by the fire.

 

[Woody girl]

I was always taught not to use rocks from riverbeds. Though have used beach rocks with no problems. In sweat lodge we used volcanic rocks. Nothing worse than sitting in an enclosed space with exploding hot rocks flying around!

 

[Robson Valley]

Our rivers and rock must be quite different from yours.
You have a lot of limestones and chalk? We don't.
When the big melt goes up top in June, you can see rocks like soccer balls and bigger being tumbled along the river bottoms.
They must be quite durable and low in porosity which could soak up any water.
Useful camp fires are rarely conflagrations which heat rock to rupture, anyway.

 

[Broch]

I confess, despite my best endeavours, I have never managed to get any rocks to 'explode' - crack and fall apart, yes, explode - no. I'll keep trying

 

[Erbswurst]

Me to.

But I never took stones out of the water and did them in the fire, so I don't know, if it's possible that they fly around.

Did anybody try it out?

I find, that is a very good question, Darryl!

 

[Robson Valley]

We do. We bring river rock home to build back yard fire pits. Our river stone texture doesn't shatter.
Nobody pulls a wet rock out of the river and heats it up. Paleo thinking to reduce injury risk, agreed?

As I said, we don't build big fires for cooking. Waste of fuel.
Cooking as in bison roasts, racks of ribs, venison or moose tenderloins, etc.

Every forest campsite that I've ever seen outside of town
already has at least one fire-tested rock ring and they are not pebbles.

The greatest risk is some idiot lighting a big, roaring crackling fire
in a new home fireplace made of bricks and wet mortar.
Thanks but I can't visit until tomorrow.

 

[Erbswurst]

It would be interesting to ask a geologic institute, if anybody tried it out.

Scientists usually try out what is possible.

Do parts of whet heated stones sometimes fly around like shrapnel ???

 

[Janne]

I know that if you wee on fire heated granite or gneiss bits will fly.
Scandinavian circumcision....

Heat alone changes the surface of both granite and gneiss. That is the reason making a fire on bedrock or large exposed rocks is banned and/ or seen as bad behaviour in Sweden.

 

[Darryl of Sussex]

I’m glad I asked. Someone must have made a video of this.

 

[Janne]

Usually guys are too drunk to both hold a camera and their male member and do both with success!

 

[Robson Valley]

Now that you mention it, I've seen lots of burnt rocks in fire pit rings.
The surface spalls off in sheets.
Just don't throw water on the ring rocks because you don't know how hot they are.those rocks.

However, it is a fact of life that the Haida people cooked to boiling in their bent-wood cedar boxes with fire heated stones.

 

[Le Loup]

How did you find out which rocks not to use around a fire? Is there a specific type and if so, what causes it to explode when heated in fire?
the simple answer has to be if in doubt, don’t but i’d still like to understand more about which rocks to use and which to avoid.

Many thanks,

Darryl

The only rocks that I know of that explode from the heat of a camp fire are rocks that have come from water, such as creek or river rocks. These rocks are so full of moisture that when heated the water within expands & so explodes the rock. Anyone woodslore wise will tell you, NEVER use rocks from a creek or river bed.
Keith.

 

[Nice65]

In the years I’ve been around fires here in chalk and flint country, the only thing that has blown have been flint nodules. These are often round in shape and hollow with small crystals inside, but I’ve found a few that I’ve cracked with a hammer to see the crystals that contained water too. Millions of years old water!

I don’t circle my fires with flint or chalk, it cuts down the heat output to the knees and feet, I’ll cut a few decent thick Beech logs or some soaked fallen Pine and use three as a backstop heat reflector.

 

[Robson Valley]

We will and we do.
That's how to boil water to cook food in a waterproof wooden box.
Do your own thing.

 

[Nice65]

We will and we do.
That's how to boil water to cook food in a waterproof wooden box.
Do your own thing.

Not boasting or anything, but many years ago me and a friend decided to disappear to our favourite spot and see how long we’d last. There’s a spring for fresh water available only when the River Arun was low tide at Littlehampton, and now blocked with a steel plate and concrete , so we had plenty of water to drink and boil. Lived in an ancient canvas bell tent on skinny sleep mats and cheap bags without a groundsheet for nearly 3 weeks. Spent the days building, carving, wood collecting, listening to Hendrix, Larry Coryell, Miles, Zappa, Don Cherry etc on a crappy cassette player that loved our most precious commodity...D-Cells. I still have a little Beech tobacco pipe I bored out with red hot tent pegs because we’d run out of Rizlas. Good times.

After a week we wanted more than tinned goods so we built a kiln like covered oven of flint and managed to create a perfect lasagne, and mix dough for pizza, or something resembling pizza that tasted pretty good. Foil wrapped pork chops with Ramson leaves and potato slices were put in to slow cook were bloody delicious. Good times, but the oven collapsed one night in a rainstorm and it wasn’t too long after that we went home to a better bath than jumping in the river between tides. A fine “life” memory that I’m enjoying writing about, I’m very fond of it.

 

[Robson Valley]

Great memory, thanks. Camp food like that never gets dull. Just don't burn it. That's all there is to camp cooking.
You poke at the fire, too hot for your hand and cook things. Add a stick or two.

My next fire pit will be big river stones. They were all once at the bottom of our rivers.
One big ring of big stones and I will fill that with more rock and sand.
Gets the fire up so we don't have to look down into it. The real fire ring of stones will sit on top.

 

[Erbswurst]

Janne, is it really possible to melt Scandinavian bedrock by using a pine or birch wood fire???

I don't have the impression. We have your stones in Brandenburg and Berlin, delivered by the glaciers in the ice age.

And I never have seen a stone which was melted by a camp fire.

I managed to break slices from a large sand rock. We slept in winter times in a cave and heated it several days with a mixed wood fire.

We dried out the rock by it and in the end parts of it came down. After I had seen that, I got the impression,that this was done exactly at this point over several thousand years. That could be the reason, why it looked like a "natural" fireplace and chimney.

We could close the entrance of the crevice with two military ponchos, and it became a very comfortable home. Would I have been a hunter in the ice age I would have decided to stay and live there.

Because that was singular in this area, I'm pretty sure, that it was an old home of somebody.