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Extracting Limestone Fossils


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Hi everyone,

Recently our group stumbled on a fossil site rich in limestone fossils of ammonites, gastropods and bivalves.

I am a school teacher for science. So I collected a many to show them to the kids. They were ecstatic about them and could not at first believe that they were touching life forms that once existed 60 million years ago.

But these are still in raw form. Many of them are still surrounded by gravel like the ammonites and bivalves and gastropods are still stuck inside the stones. Since these are made of limestones I am afraid they may break if I tried removing them improperly. Can somebody suggest a good method to extract these ... I would be very thankful

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Terry Dactyll

manu...... Its all depending on the 'denseness or hardness' of the limestone

If the limestone is quite soft that the fossils are in then using say old dental pick type implements, you could remove the surrounding rock grain by grain revealing the fossil further.... If the rock is hard, then more powerful tools are required like compressed air pens to basically do the same thing..... If the fossil is say a calcite cast contained within limestone, calcite has a slightly higer hardness value than the limestone, and gentle air abrasives can be used to tease the fossil out.... weak acids are also used sometimes in these instances ....its sometimes painstaking work, although very rewarding once you have brought back to life something that has been hidden for millions of years....

Maybe if you post a photo of a couple of your finds, someone on here who may of collected the same area as you will be able to give more specific advice to your question....

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Frank Menser

Defintely photos would help. The only thing I can add to Terry Dactyll's good advice is to consider too that some fossils are best kept in the matrix due to either fragility...

post-1313-1247589958_thumb.jpg

...aethetics, or just the fact that the matrix tells part of the story of the fossil because of its composition - including possible traces of other organisms giving a window into the world your prize came from.

post-1313-1247590592_thumb.jpg

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AS was already mentioned, it depends on the hardness of the matrix surrounding the fossil, and the depth in which it's buried in the matrix.

Most of the fossils I hunt are either in chalk (soft limestone), limestone, or a chalk/calcite combination.

If i determine the fossil is able to be, or desired to be removed, I start with a dremel with a carbide bit. I take out the obvious rock and stay very clear of the fossil. Once I get closer to the fossil, I switch to a more precise diamond bit. (This dremel is a pencil attachment for my dremel) The thing with most shellfish fossils (ammonites, mollusks, brachiopods, etc) from this area, is the shell has deteriorated and you are left with mostly a cast of the specimen. This leaves a barrier between the cast and the matrix, where the shell used to be, but is no more. Most of there will almost fall out of the remaining matrix, with the exceptional calcite concrete that will fill in there the shell once was.

Once you get the fossil out, or uncovered the way you want, the remaining limestone, chalk, or calcite can be removed with either vinegar, or HCl acid of various strengths. The acid eats away the calcium in the matrix. Most people stay away from the HCl because of the dangerous nature, and the potential for accidents, so vinegar or a weaker acid is recommended. Personally I use straight battery acid and dilute it depending on the condition of the fossil, but that's me. I'm impatient. :P On most of mine, I use battery acid full strength, and use the obvious precautionary measures such as gloves, eye protection, and always do this outside. I apply it with a Q-tip to avoid runoff to unwanted places (such as your legs)

Post up some pictures, and I'm sure we can offer some better advise. There are some people here who are truly expert preppers.

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AS was already mentioned, it depends on the hardness of the matrix surrounding the fossil, and the depth in which it's buried in the matrix.

Most of the fossils I hunt are either in chalk (soft limestone), limestone, or a chalk/calcite combination.

If i determine the fossil is able to be, or desired to be removed, I start with a dremel with a carbide bit. I take out the obvious rock and stay very clear of the fossil. Once I get closer to the fossil, I switch to a more precise diamond bit. (This dremel is a pencil attachment for my dremel) The thing with most shellfish fossils (ammonites, mollusks, brachiopods, etc) from this area, is the shell has deteriorated and you are left with mostly a cast of the specimen. This leaves a barrier between the cast and the matrix, where the shell used to be, but is no more. Most of there will almost fall out of the remaining matrix, with the exceptional calcite concrete that will fill in there the shell once was.

Once you get the fossil out, or uncovered the way you want, the remaining limestone, chalk, or calcite can be removed with either vinegar, or HCl acid of various strengths. The acid eats away the calcium in the matrix. Most people stay away from the HCl because of the dangerous nature, and the potential for accidents, so vinegar or a weaker acid is recommended. Personally I use straight battery acid and dilute it depending on the condition of the fossil, but that's me. I'm impatient. :P On most of mine, I use battery acid full strength, and use the obvious precautionary measures such as gloves, eye protection, and always do this outside. I apply it with a Q-tip to avoid runoff to unwanted places (such as your legs)

Post up some pictures, and I'm sure we can offer some better advise. There are some people here who are truly expert preppers.

Thank you for all the information. Here are the photos of some of our collection. Please have a look at these and suggest how best we could go for extraction.

post-1909-1248277955_thumb.jpg

post-1909-1248277995_thumb.jpg

post-1909-1248278026_thumb.jpg

post-1909-1248278043_thumb.jpg

post-1909-1248278063_thumb.jpg

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Some of those are pretty interesting. I would say that most of those should stay as they are. Trying to extract them would destroy them. You might be able to extract some of the fossils in that third group, but I would just leave them all as is.

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I am with Miked on this one leave as is. Maybe a little brushing with a wire brush but no more. I like fossils in matrix makes them more interesting.

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The Black Ghost

Limestone is tough. The best Ive ever been able to do is chisel fossils out of the rock. Usually there is a weak point where the fossil meets the surrounding rock. Not a professional method, of course...

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jeepinthemud

Many of them look great as they are...

If you 'extract' something too much, I find that it loses its 'fossily' look.. (Why have a fossil shell that looks like any other shell?)

I like leaving mine in matrix... (but thats just me)

And the third on in the second section looks like a septarian nodule... Look at the images on this topic.

Just my opinion.

And also for educational purposes, I think it would be good to show the material (limestone) so the students will be able to know WHY they were fossilized, along with WHAT fossilized them. Having a fossil in float, gives no indication about where its from, what it is, etc... I think the surrounding stone is part of a fossil, it is what gave it its second life.

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