Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: golaf on 18/10/2012 23:52:24
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Can you please help me identify these rocks? Thanks!!
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Here's the other rock
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Hi Golaf.
Just a quick comment on the first Pic as it is after 4am here and bed is calling. The coating of fine, clear crystals looks like drusy quartz.
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The second example appears to be a conglomerate. This is a sedimentary rock, poorly sorted, with comparatively large pebbles of varied composition set in a matrix of much finer particles. It is formed in a high energy environment, hence the rounding of the pebbles, with the matrix material being acquired in a low energy setting prior to burial.
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Thank you both! It's so nice to have such depth of knowledge on these things! I also have another rock (no picture yet) that looks like a white small brain. Almost completely round and smooth and the underside dents in a little bit. What do you think this is?
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... I also have another rock (no picture yet) that looks like a white small brain... What do you think this is?
https://www.google.co.uk/images?q=brain+coral+fossil [?]
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No, unfortunately none of these fit the bill. That's what I was thinking at first but it's very smooth. I can't seem to find any pictures online for something even similar...
I'll have to upload a photo asap!
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I'm not convinced the second picture is conglomerate- looks like some well formed crystals are present, which would be inconsistent with conglomerate. Can you get a couple of more pictures, one from further away?
Also, be careful associating fine-grained matrix material with low-energy environments. That may or may not be true.
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Unfortunately that was the only photo that I took of the rock but here's a photo of the wall that was nearby...It looked like it may have come from there. Smooth on both sides and then a line that seemed to go on and on with this type of rock.
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I'm not convinced the second picture is conglomerate- looks like some well formed crystals are present, which would be inconsistent with conglomerate.
If present the then well formed crystals would exclude conglomerate. I considered the possibility, but on balance -given the quality of the photo I remain reasonably confident that it is a conglomerate.
Also, be careful associating fine-grained matrix material with low-energy environments. That may or may not be true.
I didn't want to confuse things by discussing diamictites deposited by turbidites. I thought it might muddy the water. :) Is that what you were thinking of?
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Second specimen crtainly looks like a sedimentary rock. Clasts vary from well rounded to sharply angular. I'm not at all sure about the presence of crystals. How about a breccio-conglomerate, or a rough concrete? :)
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the wall is definitely conglomerate with a mixture of angular and rounded clasts. Matrix may be arkosic.
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Thanks everyone! Great insight!
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Okay, finally got some more photos. Here is the "brain" rock..
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The under side.
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And here is another curious rock. The rock itself is very pretty/handsome and honestly seems to be in the shape of some sort of native american tool maybe?
Thanks!!
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4607 & 4609 look very much like dreikanters. These are ventifacts produced by the action of blown sand in a desert environment. Of course, it would be necessary to have more information about hardness etc, as flint flakes can also look very much like this. The apparent absence of conchoidal fracture in these images might suggest that they are not pics of flint.
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You're correct. It's not as hard as flint is and definitely not as smooth.
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Hi Golaf.
I've just realised that no one has commented on your "brain" pics.
If you have not given up and vanished into the distance; or alternatively, identified it; a little more info would be good.
Hardness is perhaps the most significant thing to check, then, if it is markedly too soft to be quartz, try a spot of acid - HCl is ideal - to see if it fizzes.
I have found quartz pebbles fused together like this in relatively low grade metamorphics. If the process continues they tend to end up as mini boudin structures, often in mica schists.
There is probably little point in making any more suggestions until that first bit is resolved, but some idea of the environment in which it occurred could help.
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In my opinion, your "brain" rock looks like some type of feldspar, perhaps microline or orthoclase.
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I think that's a reasonable guess, Lab Rat, but some more information would still be a help, especially relating to the underside.
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Petrified Brains?
Here are a couple of rocks from our family collection.
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The first one is some kind of an agate, I think.
The second one highly resembles golaf's rock (sorry I don't have an underside photo, but I believe it had a similar graininess).
Are they both forms of agates? Water/mineral deposit formations?
Not surprising, I believe both my rocks, and golaf's rocks are Western North American rocks.