GeologyRocksStrange Metallic(?) Rock from North Africa
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Welcome to GR Desert
Mon, 08/29/2011 - 20:22Welcome to GR Desert Stumbler,
Your description is very full, but I really can't imagine what this thing looks like...a photo is really a must.
However a lot of stony meteorites are found in the Sahara, so it is likely (I feel) that there may be iron nickle meteorites as well.... and indeed can you get a mixture of the two (anyone know?).
Try a compass next to it and see if the needle deflects.
John
“Civilisation exists by geological consent, subject to change without notice.” - Will Durant
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It looks to me like a hard
Tue, 08/30/2011 - 11:40It looks to me like a hard variety of either limonite or goethite (both complex iron oxides), probably limonite, the texture is about right as it frequently forms a mamillated/botryoidal structure which is sometimes a replacement of hematite which itself is a very common mineral in desert environments and often forms reddish soils and sands.
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Having looked at some images
Tue, 08/30/2011 - 20:58Having looked at some images of the two things you suggested, I'm fairly convinced it's neither.
On another forum, after much discussion, we are tentatively going with weathered obsidian. However I have yet to measure the sample's density. Would you agree with this potential assessment?
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Having now seen the photo I
Tue, 08/30/2011 - 21:11Having now seen the photo I have to confess that it comes to mind that it may be coprolite. That can pyritise. In fact I sell quite a lot (yes, really!) which is 'turtles' from Morocco, and that is certainly pyritised. Apparently this stuff is 100 Ma and I get people pick it up and sniff it!!!!! I've told people they should wash their hands after touching....and they have gone and washed them! But the most weird was someone who listened to one. The mind boggles at what they expected to hear.
John
“Civilisation exists by geological consent, subject to change without notice.” - Will Durant
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Strange Metallic(?) Rock from North Africa
Submitted by DesertStumbler on Sun, 08/28/2011 - 23:29.Firstly, apologies for the poor quality pictures, I'll see if I can get hold of a better camera.
{Edit} I'm not sure where the photos I uploaded to this site have ended up, and Picasa is mucking me about. I'll try to sort it ASAP. {/Edit}
I stumbled across this strange looking rock in the Western Sahara earlier this year. I have very little knowledge of geology and no one I've spoken to seems to be confident of it's origin or composition. I'll describe it as best I can.
The rock appears to be comprised of large core with a thin coating of grey igneous rock, containing white and yellow crystalline structures, that has mostly chipped away. The core is very black where it is clean. It is covered in ripples down the long sides and is weirdly stippled on the top. The rock as a whole feels much heavier than it has any right to be, leading me to think that perhaps the black core is composed partly of a metallic substance. Magnets react very slightly to it, but that reaction is so small that I can't be sure if I'm imagining it! However I have only used a common fridge magnet on it so far.
I would be very interested to learn the origins of this odd lump. Current opinions I have received tend towards it being ejecta from a volcanic event, but I think it would be cool (however unlikely) if it turned out to be a meteorite. And as I've said, no one is sure, so any help would be greatly appreciated!