# rocks around a camp fire



## bronco611 (Jul 5, 2011)

Be very careful if you ever decide to place rocks around a campfire. Last year I placed some rocks around a camp fire, and I thought I had some wood which was popping. Turned out to be the rocks started to explode after they got hot. Pieces of rock started to hit us in the face, neck etc. This could cause a serious problem if it was to hit you in the eye while camping. Please be careful while camping.


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## 243Savage (Jul 5, 2011)

I've been told to especially not use rocks that came from a river or stream, as they can explode from the moisture expansion inside.


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## 3ringer (Jul 6, 2011)

Never heard of this before. Thanks


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## dawg2 (Jul 6, 2011)

243Savage said:


> I've been told to especially not use rocks that came from a river or stream, as they can explode from the moisture expansion inside.



Very true.  They can blow up like a grenade.


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## Lukikus2 (Jul 6, 2011)

dawg2 said:


> Very true.  They can blow up like a grenade.



Yes they can. Do not use river rock.


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## Nicodemus (Jul 6, 2011)

In particular, do not use chert or flint, wet or dry. Rapid temperature change in these, either hot or cold, will cause it to fracture and send off razor sharp chunks and flakes, at supersonic speed.


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## shakey gizzard (Jul 6, 2011)

243Savage said:


> I've been told to especially not use rocks that came from a river or stream, as they can explode from the moisture expansion inside.



The same with green bamboo!


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## Nugefan (Jul 6, 2011)

I have seen it my self also ...

great reminder ...


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## jason4445 (Jul 6, 2011)

This is something I have heard for years and have known rocks, river and otherwise, to explode in a fire.  In asking my geologist cousin the problem is not water but  is air bubbles in the rock.  very few types of rocks will absorb water if in a river.

In igneous and some metamorphic rocks tiny little air bubbles become trapped in it as the rock cools when originally formed. Once the little bubbles are heated the gas in them expands and you get the explosion or pop.  What is happening is rarely does the whole rock explode but layers of the rock pop off.  This is similar to putting a blow torch on concrete and a bit of the concrete will pop off, but with rocks it happens on a much larger scale.

In this area many of the rocks found in streams are granite, basalt, and types of marble that contain the little air bubbles. Also people choose the rounded river type rocks for a campfire cause they look better.

Flints and chert are particularly susceptible and will explode or flake off not because of water, but by uneven molecule expansion, but they can be slowly heated and slowly cooled which will make them easier to knap.


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## HoCoLion91 (Jul 6, 2011)

We had this happen one time while grilling.  I had used pieces of flint rock to elevate the grate holding charcoal.  Once the charcoal got hot, the rock started popping and chipping off.  We had pieces of flint in the chicken.  Luckily no one had any broken teeth.


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## Miguel Cervantes (Jul 6, 2011)

243Savage said:


> I've been told to especially not use rocks that came from a river or stream, as they can explode from the moisture expansion inside.



Yep.


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## Nicodemus (Jul 6, 2011)

Dover chert out of west Tennesee will absorb water like a sponge. Since heat treatment didn`t work on it, Indians actually soaked it in water, to aid in workability. My local Coastal Plains chert will absorb water too. I`ve spalled nodules of it and had water run out of the druzy quartz chrystals in some of it, or pockets in the stone.

If you try to use any of this for fire rocks, you`re takin` your life in your hands.


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## Randy (Jul 6, 2011)

Don't put your wife in the fire either.  She will trow rocks at you.  Don't ask me how I know.


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## 243Savage (Jul 6, 2011)

Randy said:


> Don't put your wife in the fire either.  She will trow rocks at you.  Don't ask me how I know.



Round river rocks or chert?


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## Capt Quirk (Jul 12, 2011)

What kind of rocks are good for the fire? I'm looking for a flat rock to use as a cooking surface in an adobe oven.


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## Nicodemus (Jul 13, 2011)

Capt Quirk said:


> What kind of rocks are good for the fire? I'm looking for a flat rock to use as a cooking surface in an adobe oven.



The rocks I use for my tipi fire  is schist. Choctawlb brought a load of it back from the north Georgia mountains for me. I also use it for abraders and hammerstones in my flintknappin` toolkit.


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## Capt Quirk (Jul 13, 2011)

That schist come in 3 foot slabs?


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## Capt Quirk (Jul 13, 2011)

about 2-3 inches thick?


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## Nicodemus (Jul 13, 2011)

I`m not sure Keith. My altar stone is probably 2 inches thick, 6 inches wide, by 16 inches long.

I`m tryin` to remember what Snowbear made his oven out of.


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## Capt Quirk (Jul 13, 2011)

So you know what it is I'm looking to do? Just a flat stone over a wood fired box, for breads and such.


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## Nicodemus (Jul 13, 2011)

All I have seen were all stone slabs placed in the dirt. usually in the keyhole end of a cookfire.


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