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daves64

Semi transparent shells?

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daves64

I recently bought a smallish "fossil kit" online. Just some fossils in a bag from an outfit in West Virginia. I figured there would be a lot of steinkerns & bad preservation. I wasn't wrong in that. Lots of gastropod steinkerns, mangled urchins & urchin spines & star shaped crinoid stem sections. And some shells that seem sort of crystallized that light shines through. 2 reg pics of one of the better ones + 2 pics of light shining through. Pic #5 is an edge view of one of the broken ones & #6 is what I think may be beekite, which is present on several of them. Not really concerned with shell id for the most part, more curious as to what replaced the shells to make them semi transparent like this. Almost crystallized or agatized. 

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6.jpg

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Wrangellian

Looks like beekite (chalcedony) to me. Neat little bivalve, though... does it say where it's from or how old?

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daves64

As far as I know they are from West Virginia. I'll try to contact the company to try to find out location & age. I've only got like 20+ of them, most complete or almost complete. Oddest part though is the ones that are the most transparent are also the lightest in weight. Almost like it's just the shell w/ nothing inside. Broken ones have a very hard filling that doesn't seem to scratch easily.

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digit
8 hours ago, daves64 said:

Almost crystallized or agatized. 

Given the color and translucency, I'd say you are on the right path. Assuming the calcium carbonate (aragonitic) shells were buried in a bed of silica-based sand then the permineralization during the fossilization process would have replaced the aragonite with a form of cryptocrystalline silica (chalcedony). (Listen to me--I sound like @ynot ;)). This replacement is well known in the silicified corals from the Tampa area in Florida and in the Withlacoochee River in southern Georgia. If coral skeletons can do it I don't see why bivalve shells can't. I cannot say I have specifically heard of this before but the depth of my ignorance in fossil matters knows no bounds. :P

 

Cool fossil--hope your "fossil kit" was worth it.

 

 

Cheers.

 

-Ken

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daves64
2 hours ago, digit said:

 (Listen to me--I sound like @ynot ;)). 

 

Cool fossil--hope your "fossil kit" was worth it.

 

Don't worry, it will pass... I hope :blink:

The fossil kit was only $8.00, so not too bad a deal.

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Plax

Agree with Digit. When cryptocrystalline silica or whatever fills the void of a dissolved shell is it still considered a pseudomorph? I have used the term for many years but don't see it used here and perhaps there's a better description now. Here are some dolomitic pseudomorphs form the base of the Island Creek Member of the Peedee.

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abyssunder

There is beekite on the external surface of the valves, tending to form rings in the diagenetic process. The rings might be very young in their evolution in time, according to the number of concetric rings.
You can post a sample of these to this nice thread, if you like:

:)

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daves64

Well, that was an interesting turn... Heard back from the sellers & guess what. They are apparently from Morocco & Devonian in age. As are the small urchins, large, club like urchin spines, crinoid stem pieces, corals, gastropod steinkerns & mini ammonites. I need to get some good pics of the ammonites & post them. The smallest is only 6 mm across. :blink: I guess @Tidgy's Dad strikes again. :D

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JohnBrewer

Pelisipod bivalve from Morocco, Devonion :) 

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Tidgy's Dad

Laevastarte  sp. Eocene, Dakhla, Western Sahara, Morocco. 

If I recall correctly.

I've got a few of them somewhere. 

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Zenmaster6

They remind me of the basket clam bivalves I found in the Myrtle River in Oregon

5125605625_b5999783c1_b.jpg

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