<p>What you're looking at is a <a href="https://en.wikipedia.org/wiki/Conchoidal_fracture" rel="noreferrer">conchoidal fracture</a>. It means you are looking at one half of a larger piece of flint. The strike that broke it occurred on the centre of the radial pattern, and it propagated outwards. Flints are rather hard to break, so I suspect this  means that it was either broken artificially. That is, someone broke it. Not happened naturally. These things do occasionally happen naturally, if it was thrown around during a storm or something.</p>
<p>The field of <a href="https://en.wikipedia.org/wiki/Fractography" rel="noreferrer">fractography</a> deals with the study of fracture patterns.</p>

CC BY-SA 4.0
2023-02-13T02:34:35.990Z
2023-02-13T02:34:35.990Z
Gimelist
<p>This stone was found at the beach on the Danish side of Øresund (Amager strand in Copenhagen). I believe it is flint, though I am not sure. There is a pattern of rings on one of its sides (see photos). What could be the source of that?</p>
<p><a href="https://i.sstatic.net/lGQ84.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/lGQ84.jpg" alt="enter image description here" /></a></p>
<p><a href="https://i.sstatic.net/kUcYR.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/kUcYR.jpg" alt="enter image description here" /></a></p>
<p>Thank you</p>

CC BY-SA 4.0
2023-02-06T06:21:40.413Z
it is how https://en.wikipedia.org/wiki/Cryptocrystalline rocks breaks after an impact from an other rock,glass breaks in the same way same with obsidian(volcanic glass).
trond hansen
CC BY-SA 4.0
2023-02-06T10:26:40.750Z
Universal_learner, I am sorry if the post was inappropriate. I found a similar question here when trying to find out the source of the rings... 
Thank you @trond-hansen. This is very interesting, especially that the pattern only appears at a very small section of the stone.
Osmor
CC BY-SA 4.0
2023-02-06T13:07:30.530Z
the rock is flint or obsidian,and the question is what makes the rock break in this way,so i think it is on topic but it might be a duplicate.we had a question about this a couple of years back,it was around the time when we voted rock id question as off topic
trond hansen
CC BY-SA 4.0
2023-02-07T10:40:04.777Z
Questions about rock identification have very explicitly been denoted as off-topic. The site was previously inundated with far too many poorly worded / poorly photographed rock ID questions that as a community we decided to make all such questions off-topic. I have voted to close this question as a rock identification question.
David Hammen
CC BY-SA 4.0
2023-02-07T16:59:32.103Z
It looks like flow banding: https://structuredatabase.wordpress.com/deformation-flow-banding-in-obsidian/#:~:text=Obsidian%20is%20a%20volcanic%20glass,variations%20in%20crystallinity%20or%20vesicularity.
Stevan V. Saban
CC BY-SA 4.0
2023-02-07T18:11:19.297Z
Your question (which is a good question) can't be answered without identifying the sample since that determines how the sample was formed. Get a firm identification of your sample and your question will be valid.
Stevan V. Saban
CC BY-SA 4.0
2023-02-08T11:14:38.790Z
I am sorry, I really didn't mean pollute the site. Since there are some interesting comments here and since you make it clear that such questions should not be posted, perhaps you could consider keeping the question for future seekers, like me.
Osmor
<rocks><identify-this-object>
Identify source of rings pattern in flint
Osmor
# Identify source of rings pattern in flint

(Asked by: username_0 on 2023-02-05)

This stone was found at the beach on the Danish side of Øresund (Amager strand in Copenhagen). I believe it is flint, though I am not sure. There is a pattern of rings on one of its sides (see photos). What could be the source of that?

[![enter image description here](https://i.sstatic.net/lGQ84.jpg)](https://i.sstatic.net/lGQ84.jpg)

[![enter image description here](https://i.sstatic.net/kUcYR.jpg)](https://i.sstatic.net/kUcYR.jpg)

Thank you

**Tags:** rocks, identify-this-object

> **Comments:**
> **username_1**: it is how https://en.wikipedia.org/wiki/Cryptocrystalline rocks breaks after an impact from an other rock,glass breaks in the same way same with obsidian(volcanic glass).  
> **username_0**: Universal_learner, I am sorry if the post was inappropriate. I found a similar question here when trying to find out the source of the rings...  Thank you @username_1. This is very interesting, especially that the pattern only appears at a very small section of the stone.  
> **username_1**: the rock is flint or obsidian,and the question is what makes the rock break in this way,so i think it is on topic but it might be a duplicate.we had a question about this a couple of years back,it was around the time when we voted rock id question as off topic  
> **username_2**: Questions about rock identification have very explicitly been denoted as off-topic. The site was previously inundated with far too many poorly worded / poorly photographed rock ID questions that as a community we decided to make all such questions off-topic. I have voted to close this question as a rock identification question.  
> **username_3**: It looks like flow banding: https://structuredatabase.wordpress.com/deformation-flow-banding-in-obsidian/#:~:text=Obsidian%20is%20a%20volcanic%20glass,variations%20in%20crystallinity%20or%20vesicularity.  
> **username_3**: Your question (which is a good question) can't be answered without identifying the sample since that determines how the sample was formed. Get a firm identification of your sample and your question will be valid.  
> **username_0**: I am sorry, I really didn't mean pollute the site. Since there are some interesting comments here and since you make it clear that such questions should not be posted, perhaps you could consider keeping the question for future seekers, like me.  

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## 1 answers

### Answer by username_4 on 2023-02-13. Score: 6

What you're looking at is a [conchoidal fracture](https://en.wikipedia.org/wiki/Conchoidal_fracture). It means you are looking at one half of a larger piece of flint. The strike that broke it occurred on the centre of the radial pattern, and it propagated outwards. Flints are rather hard to break, so I suspect this means that it was either broken artificially. That is, someone broke it. Not happened naturally. These things do occasionally happen naturally, if it was thrown around during a storm or something.

The field of [fractography](https://en.wikipedia.org/wiki/Fractography) deals with the study of fracture patterns.


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