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Rhombus shaped clast in conglomerate rock


Ramona

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This is a digital microscope photograph of a 4mm clast in a conglomerate rock from Franklin County, Alabama.  We have recently purchased property in this area and I am trying to learn about the rocks and minerals. We are in the Tuscaloosa Group, Gordo Formation and our county is a Super Site for the large amount of limonite-geohtite and siderite found there.  Around 300 iron mines are also in this one county, so the rocks I am finding are high in iron oxides, as you can see in this example.  I am intrigued by this one clast - this rock was broken in half and the clast is mirrored on both sides that broke. Is there any way to identify it by the same or appearance?

Thanks!
Ramona

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10 minutes ago, ynot said:

Can we see the whole rock? All sides please.

Yes, absolutely!  These are phone pics, but I can add some macro photos that would be more clear if that is helpful, too.  These photos are of half of the rock, as it is broken.  The other half is very similar (inside is a mirror image).  The first image is looking straight at the broken side of the rock, with the clast in question on the upper left hand side. 

Ramona

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There has been an ongoing discussion regarding these conglomerates on a Mindat forum.  One person suggested that they might be an older form of man made concrete (mid to earlier 1900's), which may be true, in fact.  However, others have said that the rocks lack some of the distinguishing characteristics of concrete such as air bubbles, etc.  I can provide more details photos to help determine that, if preferred?

Ramona

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My gut feeling on this is that it is just a coincidental shape, and not really anything fossil-wise.

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