Naked Science Forum

Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: frantbri on 01/01/2018 13:50:54

Title: What is this shell-shaped object I found in a pond?
Post by: frantbri on 01/01/2018 13:50:54: IMG_20171212_091451310.jpg (713.09 kB . 4618x3464 - viewed 5611 times)

I was digging in a pond in south Georgia and dug this up.

Anyone know WTF it is?
Title: Re: What is this shell-shaped object I found in a pond?
Post by: RD on 01/01/2018 18:42:52: Looks like a bigger version of this ...

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fgeoblog.weebly.com%2Fuploads%2F1%2F2%2F3%2F9%2F12392966%2F5102440_orig.png&hash=460248aaca17a8567c6d965b4a5f5fa5)
http://geoblog.weebly.com/expedition-baltic-sea

https://en.wikipedia.org/wiki/Concretion
Title: Re: What is this shell-shaped object I found in a pond?
Post by: chris on 02/01/2018 09:01:09: The examples in the wikipedia reference from @RD include these even more impressive specimens:

Concretions_Western_Kazakhstan.JPG (644.13 kB . 1920x1153 - viewed 4635 times)
Title: Re: What is this shell-shaped object I found in a pond?
Post by: syhprum on 15/01/2018 21:59:11: I was trying to post that it looked like a home made curling stone when Chris hit the wrong button on the computer and banned me
Title: Re: What is this shell-shaped object I found in a pond?
Post by: chris on 16/01/2018 09:19:58: Quote from: syhprum on 15/01/2018 21:59:11
I was trying to post that it looked like a home made curling stone when Chris hit the wrong button on the computer and banned me

I actually banned everyone, including myself, so it wasn't just you! ;D
Title: Re: What is this shell-shaped object I found in a pond?
Post by: chris on 16/01/2018 09:20:47: More seriously, I'm still not sure I understand completely how these pebbles are formed. Can someone explain?
Title: Re: What is this shell-shaped object I found in a pond?
Post by: RD on 16/01/2018 18:09:04: Similar to scale accumulating in concentric layers in a pipe, but there's no pipe, but a nucleation-site* around which the layers are deposited from mineral-rich water. Think pearl-in-an-oyster.

When eroded or broken the layers become obvious ...

(https://arkansasgeological.files.wordpress.com/2015/11/taco1.jpg)
https://arkansasgeological.wordpress.com/tag/concretions/

(* can be a fossil )
Title: Re: What is this shell-shaped object I found in a pond?
Post by: Tomassci on 24/07/2018 16:46:40: It's really simple. If I am right, the rock has stayed in water so long, that the water has eroded it into hydrodynamic shape.