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Ok - I'm lost again


hollywatertower

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I wish I would have gotten into fossils and minerals years ago! Once again, I turn to you all for a bit of help; all I know is that it looks cool; and it looks like coral. As usual, thanks in advance.

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Thanks. I bought a huge collection of Chinese antiques; and I ended up with some fossils and minerals somehow. I've never really had an interest before; but, now I really love it. Again, I appreciate the help!

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Tomorrow I'll put up some better pics of the inerds; I forgot I had a macro lens on. I was in such a hurry to put the original post up, I didn't really pay attention.

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You have an agatized coral geode, most likely from the Withlacoochee river either from North Florida or southern Georgia.

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I find it very nice. :)

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Very nice. If the other items in your purchase are this nice you did well.

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Hello,

Sacha, I have a question about this identification. How do you know that this geode corresponds to a coral? I have looked at the photos but I haven´t seen any coral structure. I don´t doubt about your identification, I only have curisosity to know what is the criteria to identify this sample. Is your experience with the same type of fosils the criteria to the identification?

I have done a internet search and I have seen a lot of this type of fosils, but only someones present clear coral structures. I supouse that the criteria to identify the other samples is the experience with these kind of fosils.

Regards

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I agree with xamageo that the exterior does not look like coral. I think the exterior in photo 1 looks more like wood. Even some of the interior structures seem to parallel the exterior. Can you see any evidence of wood structure in the chalcedony: growth rings etc.?

Here is a picture of a chalcedony cast and partial petrifaction of a piece of wood about 7cm long.

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Hello,

Sacha, I have a question about this identification. How do you know that this geode corresponds to a coral? I have looked at the photos but I haven´t seen any coral structure. I don´t doubt about your identification, I only have curisosity to know what is the criteria to identify this sample. Is your experience with the same type of fosils the criteria to the identification?

I have done a internet search and I have seen a lot of this type of fosils, but only someones present clear coral structures. I supouse that the criteria to identify the other samples is the experience with these kind of fosils.

Regards

I'm terrible at identification, so I try to limit my suggestions to items I have familiarity with. I collect regularly from the location I mentioned and have many pieces that are very similar. The coral structure would be evident in other photos. Here's a photo I posted from my last trip with a variety of pieces....one of which happens to be quite similar.

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This is a classic coral "geode ". The way they form is the coral is buried and dissolves (partially or completely.) Silica in the sand around the coral will leach the silica and deposit it in the voids where the coral was. It will also fill in the empty parts of the coral.

This process is similar to what happens in a limestone cavern.

Tony

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Will Rogers said: " Some of them didn't spring far enough."

 

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I just found 2 more of these; however, they are not cut or broken open. Does anyone have any suggestions on what to do with them; should I cut them open or leave them the way they are. I'm really curious about what's on the inside. It's kinda like Christmas; but shaking the package doesn't tell me anything!!

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It is best to cut them with a diamond blade.

You may be able to contact a local rock club that can do it for You, or knows someone who will.

In a pinch You could use a tile saw.

Tony

Darwin said: " Man sprang from monkeys."

Will Rogers said: " Some of them didn't spring far enough."

 

My Fossil collection - My Mineral collection

My favorite thread on TFF.

 

 

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This is from my handout when I would sell this sort of fossil:

AGATIZED CORALS FROM THE TAMPA FORMATION OF FLORIDA
The Early Miocene (25mybp) Tampa Formation underlies much of Florida. It is composed of soft, highly-fossiliferous limestones intermixed with sand and clay., There are several widely-separated exposures of the Tampa limestones which produce silicified corals and mollusks, the best known of which is Ballast Point on Tampa Bay. Nearby exposures of the same formation, such as at Sixmile Creek on Tampa Bay, may produce only calcareous specimens.

Many of the corals, mollusks, and other taxa of the Tampa Formation with shells or skeletons of calcium carbonate have been subjected to complete or partial silicification. This replacement has produced specimens of considerable beauty and sometimes of faithfully reproduced pseudomorphs. Most often, the original calcareous structure has been partially or wholly dissolved, and the replacing silica obscures identification of the taxon.

The process of dissolution of the calcium carbonate and the precipitation of the cryptocrystalline quartz (chalcedony) in Ballast Point corals is described by Lund in his 1960 paper "Chalcedony and Quartz Crystals in Silicified Corals." Lund says of the corals:
The silicified coral masses from Ballast Point are of varying sizes and shapes. Some are globose and range up to a foot in diameter, some are tubular, and others are irregular in shape. Many of the masses are hollow, and the preserved 'shell' is characteristically comprised of two distinct layers. The outer layer consists of replaced coral in which the features [may be] preserved in remarkable detail, and the inner part consists of either banded chalcedony or banded chalcedony over which quartz crystals have grown. Most of the hollow forms are lined with colloform chalcedony, a few are lined with small quartz crystals, and less commonly specimens are partitioned and lined with both kinds of material, each in a separate chamber.

The origin of the dissolved silica is plants and animals such as diatoms, radiolarians, and silica-secreting sponges, as well as other siliceous matter occurring in the matrix.

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