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Welcome! -- and Thanks for postingWell, to tell the truth I first thought it was a geode when I looked at the pictures. In fact, it still could be. But being a stickler for details, I know that there must be a source of silica for creating a geode. The definition of thunder egg is different than a geode - newbielink:http://en.wikipedia.org/wiki/Geode [nonactive] but both require silica.SOOO ... to help me put the rock in a specific geologic area I did a "tracert" in my Microsoft Command console window for the server in your profile. JL, it shows that you live in the Dallas area. This put this rock in a whole different geologic setting for a geode or thunderegg. In the Austin Chalk there are many, many pyrite concretions. (The stuff that turns a new white limestone building gray with the passage of time is finely disseminated pyrite.) These concretions can get quite large - several feet long and a foot or two wide. When I was in college in Austin there were many of these brought in to be cut lengthwise as we had a VERY large rock saw at that time. I believe they were found in a large road-cut when the south IH-20 rebuilding construction was being finished. These large pyrite nodules had been fractured and filled with tan and yellow calcite spar. This looks to be very similar to those. If you look closely in the lower right of the first picture you can see a fracture that can be followed into the core and all the way across it, passing just on the upper side of the clearer crystalline material in the center. IF you feel you can safely do it, try scratching the yellow-tan stuff with the tip of a knife to see if it will scratch easily. If it does, will the yellow rock slowly fizz in strong vinegar? Let us know what happens with your experiment!Oh - and by the way, how big is it? have a ruler to put beside this? The outlines of the center remind me of a small Brachiopod common in the Upper Cretaceous of Texas. The original center formed the suppoert around which the nodule formed.frethac - when your at school look in the third floor display cases in the Geology building and take a picture of these on your cell phone. Gotta brag here - frethac was admitted to the Honors Program At the Jackson School of Geo sciences - WAY TO GO !!!!!!!
I am a mud specialist.
Quote from: JimBob on 11/05/2010 17:06:07I am a mud specialist.JimBob,Does you mean like one o'thems hipperpotateramuses?
frethac - when your at school look in the third floor display cases in the Geology building and take a picture of these on your cell phone.
Gotta brag here - frethac was admitted to the Honors Program At the Jackson School of Geo sciences - WAY TO GO !!!!!!!
Well done frethack.
Quote from: JimBob on 10/05/2010 01:48:18frethac - when your at school look in the third floor display cases in the Geology building and take a picture of these on your cell phone.
JB,I take offence to the hilly billy comment! I am one!!!!! thanks you for for the information. is it worth a polish?