Iowan Posted January 4, 2015 Share Posted January 4, 2015 Hey guys, found this in a gravel bed in central Iowa and am having trouble identifying it. I had originally thought it might be a native American artifact but the members at Arrowheadology disproved that and sent me here. Any suggestions would be great. Thanks! Link to comment Share on other sites More sharing options...
DeepTimeIsotopes Posted January 4, 2015 Share Posted January 4, 2015 It's not looking like a coprolite but I could be wrong. Where did you find this in Iowa? Do you know the approximate age? Each dot is 50,000,000 years: Hadean............Archean..............................Proterozoic.......................................Phanerozoic........... Paleo......Meso....Ceno.. Ꞓ.OSD.C.P.Tr.J.K..Pg.NgQ< You are here Doesn't time just fly by? Link to comment Share on other sites More sharing options...
Iowan Posted January 4, 2015 Author Share Posted January 4, 2015 Yes I found it in Iowa. Unfortunately I don't know the age. The reason I thought it may be fossilized poo was, aside from suggestions, this auction of a rock suggested to be such looks very similar: http://s.ecrater.com/stores/16895/4f11e92d49d92_16895n.jpg I'm new to this forum so if that doesn't hyperlink I'm sorry. New pic is of the one being auctioned that looks similar Link to comment Share on other sites More sharing options...
jpc Posted January 4, 2015 Share Posted January 4, 2015 This looks a lot more like some sort of Paleozoic rock full of fossils that has been tumbled down one of the mighty rivers in Iowa. Certainly not a coprolite. I found the one you linked to. I had to search on the site to see its label. Yes, it is very similar to your rock, but it is not a coprolite either. not a coprolite Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 4, 2015 Share Posted January 4, 2015 Another vote for it not being a coprolite. Looks like a rock with some sort of inclusions. A coprolite should look like poop - look up some images of actual coprolites. I would pity any poor animal that passed anything like this! Lets also say that maybe - just maybe a fossil coprolite got tumbled in a river and didn't look poop like anymore - those inclusions should be evidence of the animals meal. To me they look crystalline and suggest that this is either fossiliferous rock or these are crystal inclusions in volcanic rock.. Link to comment Share on other sites More sharing options...
Rockwood Posted January 4, 2015 Share Posted January 4, 2015 Looks like it could be a very metamorphosed rock. Link to comment Share on other sites More sharing options...
Iowan Posted January 4, 2015 Author Share Posted January 4, 2015 Another suggestion that had yielded a similar match was diorite porphyry. I think this is probably what mine is too. Green example is from the Smithsonian national museum of natural history and the grey one is from some korearth.net Korean geology site. Link to comment Share on other sites More sharing options...
fossilized6s Posted January 4, 2015 Share Posted January 4, 2015 This looks a lot more like some sort of Paleozoic rock full of fossils that has been tumbled down one of the mighty rivers in Iowa. Certainly not a coprolite. I found the one you linked to. I had to search on the site to see its label. Yes, it is very similar to your rock, but it is not a coprolite either. not a coprolite I agree. No coprolite here. ~Charlie~ "There are those that look at things the way they are, and ask why.....i dream of things that never were, and ask why not?" ~RFK ->Get your Mosasaur print ->How to spot a fake Trilobite ->How to identify a CONCRETION from a DINOSAUR EGG Link to comment Share on other sites More sharing options...
Iowan Posted January 4, 2015 Author Share Posted January 4, 2015 I agree now that it isn't coprolite, would you guys say it's diorite porphyry? Link to comment Share on other sites More sharing options...
jpc Posted January 4, 2015 Share Posted January 4, 2015 what? you expect us to be geologists, too? Just kidding, and saying that the question is too geological for me. Or too metamorphic for me. Anyone else better at these things than me? Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 4, 2015 Share Posted January 4, 2015 I agree now that it isn't coprolite, would you guys say it's diorite porphyry? I would say so. Your new picture is much clearer and this looks like a plutonic igneous rock. A plutonic rock crystallises in the interior of the earth. You tend to get larger crystals as the cooling is slower. A porphyry is composed of large crystals or phenocrysts in a fine grained groundmass or "matrix". If your large crystals are plagioclase feldspar then this is a diorite porphyry. The crystals look like plagioclase feldspar to me but there are other tests you can use on the hand specimen, look for cleavage and hardness of the crystals. Link to comment Share on other sites More sharing options...
jpc Posted January 4, 2015 Share Posted January 4, 2015 very good, dr mud Link to comment Share on other sites More sharing options...
Rockwood Posted January 5, 2015 Share Posted January 5, 2015 I would say so. Your new picture is much clearer and this looks like a plutonic igneous rock. A plutonic rock crystallises in the interior of the earth. You tend to get larger crystals as the cooling is slower. A porphyry is composed of large crystals or phenocrysts in a fine grained groundmass or "matrix". If your large crystals are plagioclase feldspar then this is a diorite porphyry. The crystals look like plagioclase feldspar to me but there are other tests you can use on the hand specimen, look for cleavage and hardness of the crystals. Sorry if this seems rude, but if I'm not mistaken the new pictures are references not of the original post. Link to comment Share on other sites More sharing options...
painshill Posted January 5, 2015 Share Posted January 5, 2015 It is unquestionably an igneous porphyry but I would suggest it didn't originate in Iowa. The state is not noted for exposures of plutonic rocks and Iowa porphyry samples I have seen came from deep drilling, were distinctly green in colour and with much smaller flesh-coloured phenocrysts. I would say that it's a glacial cobble from elsewhere, which will make it more difficult to guess the mineralogy just by looking. Roger I keep six honest serving-men (they taught me all I knew);Their names are What and Why and When and How and Where and Who [Rudyard Kipling] Link to comment Share on other sites More sharing options...
Iowan Posted January 5, 2015 Author Share Posted January 5, 2015 Yes Rockwood you are correct, only the pictures in my original post were of my rock. The other ones were examples I had come across that looked similar. I will post some close-ups of my rock. Link to comment Share on other sites More sharing options...
Iowan Posted January 5, 2015 Author Share Posted January 5, 2015 Here's one more of mine: Link to comment Share on other sites More sharing options...
Doctor Mud Posted January 6, 2015 Share Posted January 6, 2015 Sorry if this seems rude, but if I'm not mistaken the new pictures are references not of the original post. Whoops! Yes I was confused there. And though the second picture was yours. Thanks for pointing that out Rockwood. Based on your new pictures this is most certainly a porphyry though.........right conclusion sorry....wrong reasons The phenocrysts in your porphyry certainly look like plagioclase. Sorry my rock ID is a little rusty and it occurred to me that an ultimate identification of this piece (in the absence of their being a local source - as Painshill pointed out) would be by thin section. This is when geologists take a rock sample and mount it and grind it down until it transmits light. You can then look at the mineralogy of the fine-grained stuff. Why is this important? Well we can most likely say this is a diorite or gabbro porphyry, but telling the difference between the two depends on the chemistry of the plagioclase (calcium vs sodium rich) and the proportions of other things in the groundmass (fine-grained stuff) like pyroxene, amphibole, and olivine. Sometimes you can see these crystals using a hand-lens. This diagram summarizes the classification of volcanic rocks. (note extrusive means erupted onto the surface, intrusive means intruded into the earths crust and not cooled on the surface.) Sorry for the confusion folks. Link to comment Share on other sites More sharing options...
Gen. et sp. indet. Posted January 6, 2015 Share Posted January 6, 2015 Iowan, 100% porphyry. Link to comment Share on other sites More sharing options...
painshill Posted January 6, 2015 Share Posted January 6, 2015 Iowan, 100% porphyry. What formation in Iowa (apart from glacially deposited erratics originating elsewhere) has porphyry which looks anything like that? Roger I keep six honest serving-men (they taught me all I knew);Their names are What and Why and When and How and Where and Who [Rudyard Kipling] Link to comment Share on other sites More sharing options...
donnyjoe Posted January 7, 2015 Share Posted January 7, 2015 I think he was addressing the OP, not suggesting that Iowa was the point of origin. Cogito ergo cephalalgia. Link to comment Share on other sites More sharing options...
Herb Posted January 8, 2015 Share Posted January 8, 2015 If its glacial in origin it could be from Canada. Looks like porphyry to me also, even though I only got a "B" in rock identification in college. "Absence of evidence is not evidence of absence"_ Carl Sagen No trees were killed in this posting......however, many innocent electrons were diverted from where they originally intended to go. " I think, therefore I collect fossils." _ Me "When you have eliminated the impossible, whatever remains, however improbable, must be the truth."__S. Holmes "can't we all just get along?" Jack Nicholson from Mars Attacks Link to comment Share on other sites More sharing options...
FossilFisher Posted January 12, 2015 Share Posted January 12, 2015 Ran by this post and it looks to me that I've found what looks almost exactly like this. Just south of Ledges State Park on the Des Moines River there is a flooded gravel pit that contains a localized Marmaton Group and Upper Cherokee limestone. I never got to clear of an identification when I tried. My thought is that it's delta refuse from the giant river that emptied out here in the Pensylvanian period filled with plant material (Annularia, Chordaites, Lepidodendron) locked in sand. But honestly thats just as far as I got. Link to comment Share on other sites More sharing options...
Herb Posted January 13, 2015 Share Posted January 13, 2015 FossilFisher your rocks have plant remains, the other has mineral inclusions. "Absence of evidence is not evidence of absence"_ Carl Sagen No trees were killed in this posting......however, many innocent electrons were diverted from where they originally intended to go. " I think, therefore I collect fossils." _ Me "When you have eliminated the impossible, whatever remains, however improbable, must be the truth."__S. Holmes "can't we all just get along?" Jack Nicholson from Mars Attacks Link to comment Share on other sites More sharing options...
janislav Posted January 13, 2015 Share Posted January 13, 2015 Those phencrysts look pretty pink for plagioclase. I'm more inclined towards potassium feldspar and therefore a rhyolite porphyry. The dark groundmass is problematical, but looks glassy gray, like some of the rhyolite that crops up beneath the Baraboo Quartzite in central WI. I lost $5 on that black rhyolite back in the 60s. The origin is almost certainly glacial. A precise location would help, Iowan. Link to comment Share on other sites More sharing options...
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