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Rosemary

Is this a lumen cast of a crinoid column? Secondly, is it geodized? 

lumen.jpg

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ynot

Looks like a columnal.

By the loosest definition of "geodized" it could be called that.

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Rosemary

I'm confused by what is geodized and what is not. Also, the difference btn geodized and silicified. 

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ynot

A geode os a rock with a crust/shell and a crystal lined hollow in it.

They should be easily separated from the bedrock they are found in.

They can be quartz (silicate), or other minerals.

Silicified - replaced by quartz minerals. Has nothing to do with whether it is a geode or not.

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Rosemary

A follow-up question: Are the following examples of geodized and silicified?

gcrledit.jpg

silicified.jpg

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ynot

To tell if they are silicate (quartz) a hardness test is needed. Does it scratch a knife?

Again, by the loosest definition of "geodeized", yes they are.

The second one looks like it has some "beekite" formation going on. Beekite is a form of silicate (quartz).

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Mark Kmiecik

Google "geode" and look at the images. Geode refers to a very specific type of rock.

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ynot

Your rocks would be more consistent with "midwest sedimentary type geodes" .

 

There are several differing types of "geode".

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Rosemary

Thx for the helpful information everyone. The existence of different types of geodes is likely the source of my confusion. Almost all of my fossils come from one area that was bulldozed, so I'm sifting through tons of upturned dirt.

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Fossildude19

Rosemary, your first item is indeed a lumen cast.  

Pretty one, too.  :) 

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Rosemary

Thank you. :-)

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Oxytropidoceras

Also, in terms of geodes, look up " silicified evaporite syndrome."

Some references are given at:

http://www.thefossilforum.com/index.php?/topic/66980-crinoid-blossom-found-in-east-central-illinois/&tab=comments#comment-702618

 

Also, online there is:

 

Milliken, K.L., 1977. Silicified evaporite nodules from the Mississippian

rocks of southern Kentucky and northern Tennessee (Doctoral dissertation).

https://repositories.lib.utexas.edu/handle/2152/62091

 

Yours,

 

Paul H.

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