enter image description here My Uncle got this stone from Australia and he would like to know what it is exactly

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The paper is 210 mm on the long side.

The stone feels like glass and is softer than metal. On the other side it is porous.

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Unfortunately it is not known from where in Australia.


closed as off-topic by user12525, uhoh, trond hansen, Fred, Jan Doggen Aug 30 at 13:26

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  • 1
    $\begingroup$ We will need more information to answer this question. Please follow this guide and add as much relevant information as you possibly can. $\endgroup$ – gerrit May 19 '17 at 16:27
  • $\begingroup$ What do you mean by "...softer than metal. On the other side it is brittle"? Brittle is not the opposite of hard. Hard-soft; brittle-ductile. Can you scratch it with metal? Can you break chips off it more easier than you would with metal? $\endgroup$ – Gimelist May 20 '17 at 0:00
  • $\begingroup$ What I meant was that the smooth side is hard, but softer than metal. You cannot break something off the stone anywhere. On the other side (spatially on the other side ) it is dark, see the last photo. It is not brittle. It is rough and porous. We have speculated that it is partly metal. So far no one could give a proper explanation for what it is, which is why I posted it here. $\endgroup$ – mike May 20 '17 at 4:39
  • $\begingroup$ How did you determine that it's softer than metal? $\endgroup$ – Gimelist May 20 '17 at 4:54
  • $\begingroup$ We didn't want to scratch it, so just guessed $\endgroup$ – mike May 20 '17 at 5:01

Your rock is most likely chert. First of all, it looks like chert. If you go through the shutterstock search page for chert, you will get some nice chert photographs (along with some sexually suggestive ones, no idea why).

Other things that make me think it's chert:

  1. It has sharp conchoidal fractures. The top of the first image and the right of the second is extremely characteristic of chert. These fractures are what makes chert a perfect raw material for flint stones used as tools in pre-history. See that chipped off bit in the bottom-centre of the first photo? That's 100% chert.
  2. It is hard. Although you refuse to scratch it, I can tell it from the picture. Such a rock with so much chips and fractures has no obvious scratches on it. Chert is very hard - and it is almost impossible to scratch it with a knife. Go ahead and have a try, you have my word for it (some random guy on the Internet).
  3. It has those reddish-brown bands and colours in it. Very common in cherts, usually formed by small amounts of iron. I'm guessing this is from Western Australia, where iron ore is mined from. That place is full of chert with bands like that.

I'm also suspecting that the black porous part could be magnetic. You can try that, but it could be that it's just a less-pretty part of the chert itself.

Chert is one of the most common rocks on Earth, composed of almost pure SiO2. As yours isn't particularly spectacular it probably has little monetary value.

  • $\begingroup$ Sexually suggestive?!? A peculiar Rorschach, that's for sure, you'll have to explain that one to me. $\endgroup$ – JeopardyTempest Jun 29 '17 at 3:01
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    $\begingroup$ @JeopardyTempest when you look it up on google. Don't blame me for it $\endgroup$ – Gimelist Jun 29 '17 at 3:03

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