Naked Science Forum

Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: Atomic-S on 13/10/2014 03:53:40

Title: What is this rock?
Post by: Atomic-S on 13/10/2014 03:53:40

I do not have a mineralogically correct identification of this rock. Each of the larger pieces is around 12 centimeters long; the smaller one a bit less.  The whitish parts are significantly softer than the reddish parts, and the whitish parts corrode easily by acid.  I do not know where it came from. Does anyone know anything about it?
 (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2F%5Battachment%3D19183%5D%5B%2Fattachment%5D&hash=9e87b2861da6fcb986933fec8b2fa4e2)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2F%5Battachment%3D19185%5D%5B%2Fattachment%5D&hash=4cbe3e56c3459d9df784654f20ef7420)
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Title: Re: What is this rock?
Post by: Bill S on 16/10/2014 23:59:20

Atomic-S, your pics seem to show different types of rock.  Let’s take the first Pic.  When you say: “the whitish parts corrode easily by acid.” I assume you mean they effervesce.  This certainly suggests calcite/limestone.  What about the reddish parts?  Are they hard enough to be quartz? 

Title: Re: What is this rock?
Post by: Bass on 17/10/2014 03:22:19

Hard to tell from the picture- but I have some native copper plate (very thin flat native copper) pieces that look almost identical to photo 1 and 2.  Is the reddish mineral metallic?

Title: Re: What is this rock?
Post by: Atomic-S on 22/10/2014 05:00:35

No, the material is not metallic at all. Calcite sounds like a distinct possibility for the whitish portion, but the reddish portion, which is rather dark and slightly purplish, is not affected by such acid I have used (HCl as I recall), and has a dull luster suggestive of jasper, although I have never known jasper to occur in such a color. All three pictures depict pieces of the same type of rock. In one you may notice that the outside of the rock actually is pitted, as if the white portion had been eroded away by natural processes, which would be consistent with something like calcite.  It would be interesting to know the locale of origin.

Title: Re: What is this rock?
Post by: Atomic-S on 22/10/2014 05:03:08

My experience with trying to grind this material would suggest for the reddish part a hardness comparable to jasper.  If this is a mixture of jasper and calcite, is that consistent with an igneous origin?  The randomness of the pattern, being non-stratified, seems to argue against it being sedimentary.

Title: Re: What is this rock?
Post by: Atomic-S on 22/10/2014 05:28:27

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Title: Re: What is this rock?
Post by: Atomic-S on 22/10/2014 05:29:57

Note: The appearance of swirly rainbow-light colors in the higher magnifications is an artifact of the photographic process.