What caused these rocks to form like this?

Help me identify what these stones are!

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iNat forum and iNat itself are not about rocks.

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Welcome to iNaturalist

for rocks, you could ask here: https://www.reddit.com/r/whatsthisrock/

there are other subreddits for rocks, as well.


There are some links here.

I too <3 rocks … they follow me home
Diana map of Africa 2


Interesting rocks! Unfortunately, few of us can give a good answer. Our specialties are about living things. I’m not sure where to ask – depends on where you live. Can you tell us which country or state you’re in? Maybe we can point you toward some resources.

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LInks above are good, iNat isn’t for rocks :)

Despite that, some tips:
For rock ID keep in mind It would help to know location, elevation, formation. If you know location and elevation, you can look on geologic maps to find the formation.

Your photo reminds me of chert nodules, but I wouldn’t be certain without some more information.


But we cannot fully understand living things without understanding the rocks. :)

I wish the few geology classes I’ve taken could help here but I’m afraid they can’t.


also check out the Rockd app


They look like weathered concretions.

Concretions are nodules that form when certain chemicals in the soil, or ground matrix, go into solution and precipitate out in a particular spot, cementing the sediment together, usually in a ball, often with onion-like layers.

Iron is very often a bonding agent, hence the red color of many, but iron is not the only bonding agent.

Due to the shell-like structure, when they are exposed and break during weathering the interiors erode out pretty often, leaving a hollow shell.

Concretions form in a variety of situations, and sometimes they form around fossils.


Thank you this was very helpful!

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