<p>Radial fracture is fairly common. It can form from cooling, drying mud, chemical shrinkage, impact, or several other means.  Since you are looking at volcanics you are probably looking at cooling shrinkage, The interior cools slower which means it shrinks more and that's how your get radial fractures. Fractures form perpendicular to whatever the cooling front shape is, a round shaped lava flow produces radial fractures. </p>

<p><a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.528.4436&amp;rep=rep1&amp;type=pdf" rel="nofollow noreferrer">Source</a></p>

CC BY-SA 4.0
2019-03-06T09:46:01.640Z
Rather than thermal contraction, I'm for concentric loading, because the surface isn't even. Its center is a hollow, shows collapsing. From center to the sides relief is rising concavely. Radial fractures may be fairly common in nature but there is no examples given in structural geology books, about thermal or impact related fracturing.
Muharrem Yavuz
CC BY-SA 4.0
2019-03-06T15:01:04.393Z
@MuharremYavuz generally structural geology is about large scale features, You can find some mention of it here, https://www.nap.edu/read/2309/chapter/4 I have  another paper I will add to the answer.
John
CC BY-SA 4.0
2019-03-06T22:20:34.720Z
'Rock Fractures and Fluid Flow', book will be definitely useful for whom will conduct an exploration for oil, gas, geothermal fluids etc. I like it, good authors & citations... For the case we have been discussing; this book have been mentioning columnar jointing, plumose structures, dike propogation... These are all can be found, at those structural geology books. But disappointingly, there is nothing about the radial fractures.
Muharrem Yavuz
CC BY-SA 4.0
2019-03-05T00:03:08.887Z
2019-03-06T15:13:54.093Z
2019-03-06T15:13:54.093Z
John
<p>The radial pattern of the fracture is related to a blast (probably a dynamite) not an impact. The upper part of the rock had blown out by an internal force. So the surface seen on the photographs is not an impacted surface. It is the surface of the remainder part of the original rock. In the impact crater case you might see extensionally origined tangential fractures parallel to the impact crater not the radial cracks as seen on this case.
Here is an link showing a similar deformation pattern origined by a blast.
<a href="http://www.uoguelph.ca/geology/geol2250/glossary/HTML%20files/shattercone.html" rel="nofollow noreferrer">http://www.uoguelph.ca/geology/geol2250/glossary/HTML%20files/shattercone.html</a>
Who are interested in impact craters may want to visit the link below.
<a href="http://www.impact-structures.com/" rel="nofollow noreferrer">http://www.impact-structures.com/</a>
Thanks for your replies and interests.</p>

CC BY-SA 4.0
2019-03-08T12:34:34.280Z
2019-03-08T12:34:34.280Z
Muharrem Yavuz
<p>The features probably caused by a volcanic bomb (please see my comment above). Then one may able to learn from the shape of the deformation, the location of the eruption center.
So, how to determine the kinetic energy amount of the impact, from the dimensions of the deformation features ?<a href="https://i.sstatic.net/lrSy4.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/lrSy4.png" alt="enter image description here"></a></p>

<p><a href="https://i.sstatic.net/WN90R.png" rel="nofollow noreferrer">enter image description here</a></p>

<p><a href="https://i.sstatic.net/hvQL4.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/hvQL4.jpg" alt="new photo and sketches added"></a></p>

<p>Edit: Though i gave the right answer in another post, I didn't delete this post to let anyone to see the other question in the solving process.</p>

CC BY-SA 4.0
2019-03-06T09:52:37.433Z
2019-03-13T20:57:46.773Z
2019-03-13T20:57:46.773Z
Muharrem Yavuz
<p>how can a asterisk/star like crack occur on a hard pyroclastic rock? Could it caused by a meteroite or by some other mechanism?   You may see the shape of the rock on attached photo.<a href="https://i.sstatic.net/IUoQM.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/IUoQM.jpg" alt="enter image description here"></a></p>

CC BY-SA 4.0
2019-03-04T21:01:12.587Z
Cooling units show columnar jointing and the rock observed was also a volcanic rock, so thermal contraction can be expected, i think you catch the point. i'm now searching for the examples of thermal fracturing, if one shows a pattern asterisk like. There is no folding in the vicinity, so a sheath fold occurence can't be expected.
Muharrem Yavuz
CC BY-SA 4.0
2019-03-04T21:07:11.110Z
"Could it caused by a meteroite" - no. Either internal stresses during cooling, or something hit it when it wasn't completely welded yet. It is a pyroclastic setting after all with lots of stuff flying around. No need for imaginary meteorites..
Gimelist
<geology><petrology>
how can a asterisk/star like crack occur on a rock?
Muharrem Yavuz
# how can a asterisk/star like crack occur on a rock?

(Asked by: username_0 on 2019-03-04)

how can a asterisk/star like crack occur on a hard pyroclastic rock? Could it caused by a meteroite or by some other mechanism? You may see the shape of the rock on attached photo.[![enter image description here](https://i.sstatic.net/IUoQM.jpg)](https://i.sstatic.net/IUoQM.jpg)

**Tags:** geology, petrology

> **Comments:**
> **username_0**: Cooling units show columnar jointing and the rock observed was also a volcanic rock, so thermal contraction can be expected, i think you catch the point. i'm now searching for the examples of thermal fracturing, if one shows a pattern asterisk like. There is no folding in the vicinity, so a sheath fold occurence can't be expected.  
> **username_1**: "Could it caused by a meteroite" - no. Either internal stresses during cooling, or something hit it when it wasn't completely welded yet. It is a pyroclastic setting after all with lots of stuff flying around. No need for imaginary meteorites..  

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## 3 answers

### Answer by username_2 on 2019-03-05. Score: 1

Radial fracture is fairly common. It can form from cooling, drying mud, chemical shrinkage, impact, or several other means. Since you are looking at volcanics you are probably looking at cooling shrinkage, The interior cools slower which means it shrinks more and that's how your get radial fractures. Fractures form perpendicular to whatever the cooling front shape is, a round shaped lava flow produces radial fractures.

[Source](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.528.4436&rep=rep1&type=pdf)

> **Comments:**
> **username_0**: Rather than thermal contraction, I'm for concentric loading, because the surface isn't even. Its center is a hollow, shows collapsing. From center to the sides relief is rising concavely. Radial fractures may be fairly common in nature but there is no examples given in structural geology books, about thermal or impact related fracturing.  
> **username_2**: @username_0 generally structural geology is about large scale features, You can find some mention of it here, https://www.nap.edu/read/2309/chapter/4 I have  another paper I will add to the answer.  
> **username_0**: 'Rock Fractures and Fluid Flow', book will be definitely useful for whom will conduct an exploration for oil, gas, geothermal fluids etc. I like it, good authors & citations... For the case we have been discussing; this book have been mentioning columnar jointing, plumose structures, dike propogation... These are all can be found, at those structural geology books. But disappointingly, there is nothing about the radial fractures.  

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### Answer by username_0 on 2019-03-08. Score: 0

The radial pattern of the fracture is related to a blast (probably a dynamite) not an impact. The upper part of the rock had blown out by an internal force. So the surface seen on the photographs is not an impacted surface. It is the surface of the remainder part of the original rock. In the impact crater case you might see extensionally origined tangential fractures parallel to the impact crater not the radial cracks as seen on this case.
Here is an link showing a similar deformation pattern origined by a blast.
<http://www.uoguelph.ca/geology/geol2250/glossary/HTML%20files/shattercone.html>
Who are interested in impact craters may want to visit the link below.
<http://www.impact-structures.com/>
Thanks for your replies and interests.


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### Answer by username_0 on 2019-03-06. Score: 0

The features probably caused by a volcanic bomb (please see my comment above). Then one may able to learn from the shape of the deformation, the location of the eruption center.
So, how to determine the kinetic energy amount of the impact, from the dimensions of the deformation features ?[![enter image description here](https://i.sstatic.net/lrSy4.png)](https://i.sstatic.net/lrSy4.png)

[enter image description here](https://i.sstatic.net/WN90R.png)

[![new photo and sketches added](https://i.sstatic.net/hvQL4.jpg)](https://i.sstatic.net/hvQL4.jpg)

Edit: Though i gave the right answer in another post, I didn't delete this post to let anyone to see the other question in the solving process.


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