Went out looking for meteorites but found this instead.
It looks like a fossil, but a fossil of what?
Regards
Steven
Hi Steve,I got this message from Carl Tanner.
Quote)
That is most likely a fusulinid limestone. Fusulinids are a type of foram, basically a plankton with a hard shell made out of calcium carbonate.
He would like too know where you found it ?
Cheers
Hi Steve,I got this message from Carl Tanner.
Quote)
That is most likely a fusulinid limestone. Fusulinids are a type of foram, basically a plankton with a hard shell made out of calcium carbonate.
He would like too know where you found it ?
Cheers
Thanks for your efforts Ron.
Unfortunately the fossil was found at the edge of a dirt road so it doesn't constitute as in-situ discovery.
Perhaps it was disturbed and is local to the area, in which case it was located in The Brisbane Ranges Victoria at coordinates near 37 degrees 51.575 minutes South and 144 degrees 111.425 East.
My geological map of the region indicates the rocks of the area are mainly from the lower Ordovician period.
Give my regards to Carl and ask him why he no longer posts here.
That's a bit of a problem with working from images. To me they look like quartz phenocrysts in a porphyritic rhyolite, especially because of the crystalline habit, which you would not expect in a fusilinid.
Best way for you to tell is to drop a bit of pool acid on the rock. If it goes nuts = limestone. If not = rhyolite.
Cheers,
Andrew
That's a bit of a problem with working from images. To me they look like quartz phenocrysts in a porphyritic rhyolite, especially because of the crystalline habit, which you would not expect in a fusilinid.
Best way for you to tell is to drop a bit of pool acid on the rock. If it goes nuts = limestone. If not = rhyolite.
Cheers,
Andrew
Thanks Andrew.
There is a mild reaction when battery acid is added to the rock, nothing like a violent effervescent reaction once would expect if it was limestone however.
I have taken some microscope shots of the rock.
These might prove useful.
I'm even more convinced that those are crystals and not fossils and you have a porphyry. How fresh is the surface? Ideally you need to split open a big chunk of rock to get an unweathered surface to look at.
The only thing that bugs me is that those phenocrysts look more like hornblende in shape - but the colour is all wrong for it to be mafic, which is why I think it's a rhyolite.
Anyway - to be sure, crack it in half, give it a wet sloppy lick, and take another photo.
Cheers,
Andrew.
There is a mild reaction when battery acid is added to the rock, nothing like a violent effervescent reaction once would expect if it was limestone however.
I have taken some microscope shots of the rock.
These might prove useful.
Regards
Steven
The reaction of limestone and acid is not that violent. I think it's to do with the limited surface area (compared to a powder) and the presence of clays etc in the limestone.
Last week a tech from Chemistry asked me for some limestone for a first year chem prac. They needed a steady stream of CO2 and were finding that powdered CaCO3 (or Na2CO3 - I'm not sure) was producing the CO2 too fast and then was all consumed. I found him some calcite and some coral (diagenetically altered and infilled) which apparently worked OK.
Depends on the form of the calcite, the dilution of tha acid etc. but in the past when I've stuck a drop of HCL on a lump of limestone it bubbles up immediately and unmistakably. Never used battery acid so can't comment on this experiment's result. That is why geologists carry a small bottle of HCL in the field and have done for centuries. It works to identify carbonate in the manner described.
Cheers
Andrew.
Hornblende does. But you're only dealing with the oxidized outer skin. Streak is only useful for individual minerals, not whole rocks. So I'm starting to think you are holding a weathered hornblende porphyry.
The flat crystal faces of the 'fossils' and their polygonal cross-section indicate that they are crystals and not fossils. Sorry.
I decided to purchase some HCI and try the test.
A drop was applied to the rock and allowed to evaporate.
The reaction was fairly inert to the naked eye but under a microscope the picture was somewhat different.
There where some micro structures that were clearly effected by the HCl.
The attached image shows a suspiciously segmented "thing" that was either dissolved or washed away by the HCl.
The presence of a "residue" in the after picture suggests it was dissolved.
Where as my initial reaction was that the rock does not contain fossilized structures, I'm not too sure now.
Regards
Steven
PS. I'm aware that segmented structures don't automatically point to fossils as illustrated by the Martian "fossils" found in Antarctica debate a few years ago.
That's actually pretty diagnostic. It's not limestone. Whatever you dissolved on the surface is not really of interest - it really has to be a freshly exposed surface to be meaningful- but if it was carbonate the little drop of HCL would have filled with bubbles. I've got a strong feeling if you did crack this open you would find that the matrix is quite dark and it's volcanic.
Mind you, I'm only a professional geoscientist with 20+ years experience. I'm often wrong and haven't even held the rock in my hand, so you can believe it's whatever you want it to be
Cheers,
Andrew.
I hope I'm not coming across as dogmatic or augmentative.
I respect your opinion, you have 20+ years experience as a geoscientist, I flunked out in first year geology at Uni. (A reflection on my bad attitude at the time when I had a personal war with the entire geology department.)
Many rocks with an overall fine-grained texture display scattered minerals that are more than 1 mm across. This porphyritic texture indicates that the magma sat and cooled a bit below the Earth's surface, thus giving time for the large crystals to grow, before erupting onto the surface and cooling very quickly. The large crystals are termed phenocrysts while the aphanitic rest of rock is called the groundmass. The rocks below cover mafic, intermediate, and felsic compositions (top to bottom).
I'm not in the least bit offended! I can see how I might have sounded that way - no I'm serious, without actually holding the thing in my hand, sniffing it, cracking it open and licking it, it could well be just about anything at all! The HCL test does tell me it aint carbonate (limestone), though.
Although my wife (geology PHD, I'm actually a geophysicist with an extra undergrad degree in geology) thinks I'm right too. This is very unusual... normally when you show two geologists the same rock you will get three opinions. It's taken me 20 years to learn that you can be wrong about stuff and that it's not necessarily a bad thing.
And as I'm fond of shouting at my peers, and to quote the great Sheldon Cooper - 'geology isn't real science'
cheers,
Andrew.
Quote:
Originally Posted by sjastro
Thanks for your feedback Andrew.
I hope I'm not coming across as dogmatic or augmentative.
I respect your opinion, you have 20+ years experience as a geoscientist, I flunked out in first year geology at Uni. (A reflection on my bad attitude at the time when I had a personal war with the entire geology department.)
