Fossil Or Pseudomorph?

[briman]

Hello Forum,

Here are a couple of fuzzy photos of some enigmatic cretaceous material from central Texas (still haven't finished the learning curve with this new camera). This strange chert is from the Ft. Terrett formation in Gillespie county. The diamond to triangular pattern on the surface is the ends of columns cemented with a pale matrix. Each column has varying layers of concave banding (think stromatolite). The adjacent columns have the same pattern in terms of band width/spacing. The shape of entire specimens would appear to be a low dome with some having a central peak of progressively taller columns. The invertebrate paleontology lab at the Texas Memorial Museum came out and collected samples a couple of years ago- the last time I checked they had reached no concensus.

The local indians used some of the fine-grained pieces to fashion artifacts and many pieces are fractured from their sampling.

Thanks for looking,

Brian

[JimB88]

They kind of look like agate nodules to me.

[JohnJ]

Hi Brian,

Welcome to the Forum.

You might try using the macro function on the camera if your taking photos closer than a couple feet away. Also, I'd be inclined to think the along the lines of pseudomorph - possibly a silicate replacement of calcite crystals (if that's possible). As you probably know, the contact area on the seams of chert in the Ft. Terrett are full of unusual shapes, some of which do include fossils.

[Wakaritai]

I don't see anything resembling a fossil (though the pictures are blurry). Try taking more images at different distances from the specimens to see if it helps. It looks like chert or flint (which is primarily quartz), and some of the pieces seem to have crystals on them (calcite?). It looks like they were once part of a geode that broke, or a gap between rocks underground where water could trickle through at some point in the past, depositing the crystals.

Edited May 17, 2010 by Wakaritai

[briman]

Here are a couple of better images of the material. I came up with my guess a while back but I wanted to know what others think.

Thanks,

Briman

[briman]

My images are still too blurry but I figured out macro (more or less). I will try again.

[briman]

Ok here are some clearer images. I put what I think the material is under a posting I made in board news- member introductions- central texas finder- #12.