Help With Some Odd Rocks

[Billco]

I was hunting for arrowheads when I found these rocks in the bank of a creek bed. I spend a lot of time searching for arrowheads and I have never seen rocks like these. They were about three to five feet from the surface. They appear to be chert of some sort. How did they take on these shapes? The third one was protruding from the creek bed. I broke it when I tried to dig it out of the bed. The fourth picture is the break in that rock. The last picture is the creek bed. Location: North Central Alabama.

 

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[BurntBear]

Those appear to be some unusual Chalcedony/Agate specimens. This page might familiarize you with some of it's characteristics:

Chalcedony - a Gemstone - DesertUSA

 

[Billco]

Thanks. That link was interesting.

 

[DDancer]

My guess would be limestone concretions for the big stuff~ possibly a chert in the 4th photo and a quartzite or granite in the 3rd picture. The creek looks to be fractured limestone. In the first picture the one on the end could use a close up.