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For many years now it has been fashionable to cook your food on a 'hot rock' in restaurants. What is the rock that is used?

I live in an area where volcanic rock is available (on the side of the road). So can I simply take a bit, smooth it down, heat it up and create the same effect as my local eatery? Or would I be infusing my food with all sorts of nasties?

  • Serpentine might be best to avoid, given the "serpentine barrens" that result from such. – thrig Apr 1 '17 at 14:27
  • A quick Google search should give you plenty of results. – Cindy Apr 1 '17 at 14:58
  • I don't know what they do use, but it's pretty solid - there's a lot of variety in volcanic rock, from pumice to obsidian. Can you be more specific about what this rock looks like or maybe add a photo? – Catija Apr 1 '17 at 15:14
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    Yup will put a photo up soon, also to other comment, surely google could do everything we do here? – dougal 5.0.0 Apr 1 '17 at 15:40
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    There's nothing wrong with asking simple questions - Google isn't always right. cf: meta.stackexchange.com/questions/5280/… – Catija Apr 1 '17 at 15:44
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Try granite.

I have used water-smoothed granite cobbles (~ 1 kilo) as key ingredients for making 'stone soup' (AKA Minestrone ala Lithos) with no ill effect to myself, family or guests. However, this use keeps the stone's temperature low, geologically speaking. Granite is used for countertops; most types have little I worry about, but your milage may vary.

I suggest that whatever you use, you:

Identify the type of rock, and check for any worrisome constituents. (No peacock copper {arsenic}, Galena {lead}, or Pitchblende (radioactives.) Corolary: if you can't identify it, don't muck with it (much like wild mushrooms.)

Sterilize it well. I boil mine for at least 15 minutes.

If going for high heat, do several heat/thermal-shock tests, wearing some sort of eye protection, before using the stone around anybody else.

Hope it turns out well!

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For hot rock cooking, you want four properties of the stone:

  • A smooth, non-porous surface.
    This is almost (ok, at least a bit) like a non-stick surface and means you can clean it afterwards. Neither food nor detergent should "seep into" the stone.
  • High thermal mass.
    You want to make sure that your stone is not significantly cooled down by your food as this would interrupt your cooking process and increase the likelihood of the food sticking to the stone.
  • Relatively resistant to temperature change.
    During its use, a hot stone will be repeatedly heated up and cool down again. This can cause small cracks or unevennesses to widen and destroy the material.
  • Food safety.
    The absence of toxic minerals that could leech into the food. Probably a pretty self-evident point.

I can not answer this for the volcanic rocks you can get your hands on, although some like pumice are obviously out. But I'm not a geologist. Note that a standard hot rock material would be granite. If your candidate fulfills the four criteria above, go for it.

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  • I will look for 'candidates' for my rock, do a bit of DIY on them and try them out, hopefully at some point will be able to report back with my finding, thanks for the answer. – dougal 5.0.0 Apr 2 '17 at 5:06

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