Frog effigy - my favorite find

[painshill]

springcreekoutdoors wrote:

Maybe some paleontologists can step in here, what material would a fossil 'seem' to be made of, and how heavy would it be?
That's a cute meme, thanks for the laugh

  Folks are loosely referring to it as a "fossil" but strictly speaking it's not. It is - as I said - a "steinkern", which translates from the German as "stone cast". It's a common occurrence when something hollow (like a bivalve shell) fills with minerals and sediments after death as it fossilizes which then harden to form a cast of the interior of the shell. The shell itself normally fossilizes as aragonite which then typically converts to calcite and is subsequently lost by weathering/erosion. All that's left is that internal cast, approximating to the general shape of the shell but without the detail that was originally present on the outside of the shell itself. Steinkerns are usually composed of lithified mud and/or sand cemented with carbonates or silica. They have the hardness and density of rock because that's what they are... usually limestones, mudstones or sandstones.

[Hoss]

Interesting what county and state is it from?

[rmartin]

As Josh has said, rarely do "Professionals" grace their presence on collectors forums. Arrow, Clovisoid, CMD, and particular Painshill are very knowledgeable when it comes to this sort of thing. Personally, I don't see the work on this I would expect to see on an artifact.

[Olden]

.
Just a few other examples of steinkerns.

https://www.google.com/search?q=clam+steinkern&client=firefox-a&hs=X50&rls=org.mozilla:en-US:official&channel=np&source=lnms&tbm=isch&sa=X&ei=wmUXVOG-AcvgoAScr4H4Bg&ved=0CAgQ_AUoAQ&biw=1338&bih=658

[SDhunter]

Olden wrote:

 

  Okay,  now that you posted this picture,  I do see some resemblance.         :side:

[archaic]

If this is a clam I would like to know what species it is. It seems very different from all the ones I can find. It is very smooth and uniform unlike the clam fossils I have found. Protocardia texana does not seem to be consistent at all. If it is a clam does anyone know of someone that could positively identify it?

[painshill]

archaic wrote:

If this is a clam I would like to know what species it is. It seems very different from all the ones I can find. It is very smooth and uniform unlike the clam fossils I have found. Protocardia texana does not seem to be consistent at all. If it is a clam does anyone know of someone that could positively identify it?

  Repeating what I have already said... it's from one of a group of possible genera within the overall clam family known collectively as "heart clams". It's NOT a fossil... it's a steinkern (an internal cast that has none of the original organism present). That's why it's smooth and lacking any detail, coupled with the fact that it's eroded. If you have a bivalve shell handy (any unfossilized shell) then take a look at the inside and compare it to the outside. The inside is smooth and merely an approximate representation of the exterior shape. Protocardia is one of several heart clam genera and probably the most common but there are others. It's not usually possible to identify a steinkern down to genus level, never mind species level because steinkerns don't have the features of the exterior shell which are the diagnostic features necessary for identification. If the original poster were to provide details of exactly where it was found then it might be possible to narrow it down further based on likely stratigraphy. A more positive identification will come from the fossil record of the location... not from the features present on the steinkern itself.