All the Echies (of Texas) 4 - A clump of Coens and Vinegar Cleanup!

[JamieLynn]

Went out with the Paleontological Society of Austin Saturday for a field trip - yes, in Austin Texas in August (not usually a great idea) but we went early to beat the heat and had an unusually cloudy morning with very low humidity, so it was actually VERY pleasant! We hit up a Walnut Formation road cut with lots of lovely gastropods (Anchura, Tylostoma and Gyrodes),  some rather uncommonly found Parasimilia corals plus a variety of Echinoids. I found a large 3/4 busted up Phymosoma, a number of little Loriolias, and a couple of nice Heteraster Heart Urchins but my faves were a BIG kind of busted up Coenholectypus and a tiny Coen too.

 

I picked up a number of other things, including what I THOUGHT were two squished Porocystis globularis (Algeal Fruit) which when I got home, turned out to be two nice middle sized Coens very very encrusted in limestone...so much so I did not recognize them in the field. So I thought I'd try the vinegar soak I'd heard about. I have been hesitant to try but since I already had a couple of decent specimens of Coens, I thought I'd try. WOW. Just WOW. I forgot to take a before picture, just know that they were barely recognizable! After that luck with the Coens, I decided to try it on a Goniopygus that was so encrusted you could only see a small section of it. I am SO excited with the way it turned out! So yay for vinegar soak! 

 

 

Vinegar soak on the Goniopygus

 

[Scylla]

Nice, how long a soak and what strength vinegar?

[facehugger]

Nice finds! Last weekend was pleasant, I was hitting road cuts just a little north of ya...

[FossilDAWG]

Be sure to neutralize the vinegar soak.  Several changes of water, and maybe a soak in some water with baking soda (sodium bicarbonate) to neutralize the acid, would be called for.  Otherwise residual acid that soaked into the fossil could continue to etch the fossil.

 

Don

[JamieLynn]

 

15 minutes ago, Scylla said:

Nice, how long a soak and what strength vinegar?

 

I will definitely add some baking soda to my rinse!  Straight distilled white vinegar- I was doing a two minute vinegar soak, then rinse in water and brush with toothbrush, then back to vinegar and repeat. Did that for 45 minutes and then let soak in fresh water for 3 hours.

[JohnJ]

@JamieLynn if you were able to look at your specimens before the vinegar soak, you would likely see that the vinegar has etched, or removed, fine details of surface texture.  I definitely understand the desire to see these little jewels unlocked from the matrix.  It seems using chemical preparation is always highly dependent on each individual specimen.

 

I've found that pre-soaking in water seems to mitigate chemical absorption into the fossil.  Also, scrubbing with an old toothbrush dipped into the vinegar will lessen the chances of etching the echinoid.  Doing this prep using a magnifying visor will help immensely.

[JamieLynn]

@JohnJ - aw heck...i see what you mean. Some of the smaller surface nodules are gone. Well, this one was SO encrusted, with only that one little "slice" of the urchin visible, I guess it was worth it. So really, just better to find a more perfectly preserved specimen. 

[FossilDAWG]

I often will use needles, the kind you use to inject insulin for example, to prep such fossils.  The needles are very sharp and are beveled to a sharp point (sharp enough to penetrate skin), and they serve very well to pick off grains of matrix.  A larger needle can be used on thick patches of matrix.  It's always best to work under a microscope or magnifying visor.  Never dig the needle directly into the fossil, always work parallel to the fossil surface.  Be careful as the needles are very sharp and can easily scratch calcite (which is what echinoids are made of).  You might be able to get needles with syringes (which make great handles) at a pharmacy or a farm supply store such as Tractor Supply.  You can get a magnifying visor at Harbor Freight.

 

Don

[JamieLynn]

so something as encrusted as the goniopygus would be worth using needles on?  How long would something like that take? Aprox....

[Rcotton1]

I am just archiving a 1925 Argentina collection that has been hidden since 1935 and have about 50 fruits, nuts, and a few seeds, see below, would you soak these? Were the ones you found dark like these?

[JamieLynn]

@Rcotton1 - are those fossils? Or are they actually dried vegetation?  What I found are sea urchin fossils, not seeds. I would not soak vegetation in vinegar. 

[Rcotton1]

Thank you, it is fossilized ground cherries (vegetation), here is a pic of what they looked like 54 Ma years ago. They are stone now but a few of them have the husk tops which were paper thin at the time of fossilization

[Scylla]

Those look like ironstone or siderite concretions. See the cemented sand grains? They sometimes do preserve fossils in them like in Mazon Creek material. I would post them in the fossil ID section with good close up pics.

Edited October 4, 2019 by Scylla
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