PA Fossil Finder Posted February 17, 2014 Share Posted February 17, 2014 I recently received a sample of Harding Sandstone from another member here on the forum. This Harding Sandstone is Ordovician in age and was collected from an outcrop near Canon City, CO. It is known for its early vertebrate remains. I tried dissolving a small piece in vinegar, but I didn't see any bubbles like I normally see when dissolving limestone. So then I switched to hydrogen peroxide, but again I didn't see bubbles. So I put it back in vinegar for. What should I try to dissolve this stuff with? Stephen Link to comment Share on other sites More sharing options...
Taogan Posted February 17, 2014 Share Posted February 17, 2014 (edited) Sandstone is silica, silica doesn't dissolve easily. If it is held together with a calcareous cement then acid will in time separate the grains but you won't get the same dramatic effect of dropping limestone into acid. If you are really set on separating the grains then I would suggest dilute acetic acid (vinegar) and leave it for a few weeks to see if the sample turns into sand, but this might destroy any fossils present depending on how they are preserved. Mechanically breaking up a sample may give better results, I sometimes shake more recent sandstone apart using an engraver, but again there is a risk of damaging things. Edited February 17, 2014 by Taogan Link to comment Share on other sites More sharing options...
PA Fossil Finder Posted February 17, 2014 Author Share Posted February 17, 2014 Then this must be extremely fine grain sandstone. It actually looks more like red shale. The fossils I am interested in are actually chitinous or otherwise resistant to acetic acid. Stephen Link to comment Share on other sites More sharing options...
Taogan Posted February 17, 2014 Share Posted February 17, 2014 I've looked into this a bit more and dilute acetic acid and time is the best way, how long depends on the size of the pieces, followed by wet sieving with a 0.5 mm mesh then drying and manual sorting under a low power microscope, the fossils are between 1 and 2 mm . The yield is low, about 1% of the matrix is fossil material so bulk processing is recommended to get anything at all. Fine grain non calcareous rock can take a while for the acid to penetrate all the way in, so get a good book to read while you're waiting. It looks a bit like the red marl I processed a few years ago to get some Triassic mammal material. That took more than half a year in formic acid and then I washed the teeth out of the sludge. It might take a long time but you end up with fossils that nobody else has, you just have to have patience. 1 Link to comment Share on other sites More sharing options...
PA Fossil Finder Posted February 17, 2014 Author Share Posted February 17, 2014 How many times should I change the vinegar? Stephen Link to comment Share on other sites More sharing options...
fossilcrazy Posted February 17, 2014 Share Posted February 17, 2014 I haven't worked on this, but I think freeze/thaw might work. Pulverizing may make the conodont elements not survive the process. The fish scales and teeth are Phosphatic and should hold up well to strong acid. Like you said if it didn't fizz, then Calcium Carbonate probably isn't the cementing agent. The microfossil collectors that asked for samples wanted the broken down mud and soil below the Harding SS. I think they were looking for the conodonts. An Ebay dealer from Tennessee/UK "KDfossils" sells the extracted fossils and good photographs of what is found in the Harding SS. I don't know how inclined he would be to say how he separates the fossils from matrix. I'm curious about the Hydrogen Peroxide. Did you use the 30% concentration? Supposedly the H2O2 oxidizes the organic compounds that hold matrix. I just might experiment with Quaternary-O or Rockquat to see if those will break Harding SS down softly. If that works to free those beautiful Astraspis and Eriptychius fish scales; that would be the way to go. 1 Link to comment Share on other sites More sharing options...
mikecable Posted February 17, 2014 Share Posted February 17, 2014 (edited) How many times should I change the vinegar? I'd buy a cheap digital pH meter--less than 8 bucks on Amazon. When the solution approaches a pH of 7 or neutral it's time to change the vinegar. You could probably do a taste test instead--if it doesn't taste like vinegar the reaction is over. Distilled white vinegar will have a pH of 2.5 to 5.0. The lower the number the higher the acidity. It will range in percentage of acetic acid from 5% to 10%. Cheap dollar store/generic vinegar will tend to have a higher percentage of acid, and thus be more acidic. Heat, pressure and mild agitation will speed up chemical reactions. You might consider placing your container in direct sunlight, mild heat from a hot plate or the stove, or the pressure cooker trick in a different thread. An ultrasonic cleaner would provide mild agitation. I've found that Oxyclean or its equivalent will speed up some reactions as well. It's basically anhydrous hydrogen peroxide, and the release of tiny oxygen bubbles serves to mildly agitate the solution, and as micro-fissures form in the matrix as a fracking fluid as well. Edited February 17, 2014 by mikecable Link to comment Share on other sites More sharing options...
Taogan Posted February 17, 2014 Share Posted February 17, 2014 (edited) When I do this sort of thing I don't change the acid very often, maybe once a month, or I just top it up. I tried using stronger acids and speeding up the process by changing them more frequently but all I ended up with was brittle fossils that couldn't be handled. I just keep it slow and gentle, I wouldn't recommend a taste test unless you are sure of what secondary minerals are in the sample. Edited February 17, 2014 by Taogan 1 Link to comment Share on other sites More sharing options...
PA Fossil Finder Posted February 17, 2014 Author Share Posted February 17, 2014 Thank you all for this great advice! I have 30% hydrogen peroxide but I am afraid of trying that. I have the container in direct sunlight right now. I also don't want to crush the rock much because the sample I did crush to test on had some nice fossils in it that are now in separate pieces. Every fresh break on this stone that I make, it both breaks and exposes lots of what look like placoderm armor/scales. Stephen Link to comment Share on other sites More sharing options...
PA Fossil Finder Posted February 17, 2014 Author Share Posted February 17, 2014 I checked the sample at the end of the day, it was a tiny bit dissolved. Vinegar will probably work, but take a long while. Stephen Link to comment Share on other sites More sharing options...
Taogan Posted February 17, 2014 Share Posted February 17, 2014 Just have patience, everything comes to he who waits. My record for this sort of thing is close to a year, but I got everything out intact. I don't think this will take anywhere near that long, but it may take a few weeks. 2 Link to comment Share on other sites More sharing options...
mikecable Posted February 18, 2014 Share Posted February 18, 2014 Just have patience, everything comes to he who waits. My record for this sort of thing is close to a year, but I got everything out intact. I don't think this will take anywhere near that long, but it may take a few weeks. I agree. Link to comment Share on other sites More sharing options...
PA Fossil Finder Posted February 18, 2014 Author Share Posted February 18, 2014 I put the entire sample in vinegar yesterday. I've actually seen some nice results already. It has started developing thin cracks across the surface, and bubbles a little. Should I help the cracks by prying it apart, or should I just leave it? If I try to pry them apart, it will help the vinegar into the rock - but at the same time I might accidentally break a fragile fossil inside. Stephen Link to comment Share on other sites More sharing options...
squali Posted February 18, 2014 Share Posted February 18, 2014 Your not waiting........ It's hard to remember why you drained the swamp when your surrounded by alligators. Link to comment Share on other sites More sharing options...
Auspex Posted February 18, 2014 Share Posted February 18, 2014 Patience, Grasshopper... "There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant “Try to learn something about everything and everything about something.” - Thomas Henry Huxley >Paleontology is an evolving science. >May your wonders never cease! Link to comment Share on other sites More sharing options...
PA Fossil Finder Posted February 19, 2014 Author Share Posted February 19, 2014 (edited) I am sooo impatient... But, on the small sample, I tested the freeze/thaw cycle and it was amazing. It practically disintegrated the entire thing! I think the larger bony plates are porous, because they absorbed a lot of vinegar when I rubbed it over the surface. This means that if I try the freeze/thaw cycle on the big rock, the water in the fossils could expand and break all the amazing placoderm plates and shark denticles! I am testing it again on a smaller sample, just to see. UPDATE: I was right... I am glad I didn't do this on the big sample. Freezing destroyed most of the fossils. Edited February 19, 2014 by PA Fossil Finder 1 Stephen Link to comment Share on other sites More sharing options...
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