<p>These are most likely manganese dendrites. It is not a fossil, and not organic. These usually form in cracks in rocks, and most likely this slab was broken along an existing crack.</p>

<p>You can read more about it now: <a href="https://www.mindat.org/min-26645.html" rel="noreferrer">https://www.mindat.org/min-26645.html</a></p>

<p>One comment: this is not basalt. Basalt is black. Most likely some form of limestone.</p>

CC BY-SA 4.0
2019-11-22T07:52:12.523Z
2019-11-22T07:52:12.523Z
Gimelist
<p>They are quite pretty, but they are not fossils. They remind me of the patterns that frost sometimes makes on window panes. A similar process is at work here, though with mineral bearing water infiltration rather than frost being the cause. The water infiltration deposits crystals in the rock.</p>

CC BY-SA 4.0
2019-11-21T19:46:52.647Z
2019-11-21T19:56:41.430Z
2019-11-21T19:56:41.430Z
Michael Walsby
<p>During one of my walks through the city streets, I noticed that some basalt blocks that make up the sidewalk have in their surface some very curious natural patterns:</p>

<p><a href="https://i.sstatic.net/DlBWh.jpg" rel="noreferrer"><img src="https://i.sstatic.net/DlBWh.jpg" alt="enter image description here"></a></p>

<p><a href="https://i.sstatic.net/TFuUE.jpg" rel="noreferrer"><img src="https://i.sstatic.net/TFuUE.jpg" alt="enter image description here"></a></p>

<p><a href="https://i.sstatic.net/udcDP.jpg" rel="noreferrer"><img src="https://i.sstatic.net/udcDP.jpg" alt="enter image description here"></a></p>

<p><a href="https://i.sstatic.net/1lnff.jpg" rel="noreferrer"><img src="https://i.sstatic.net/1lnff.jpg" alt="enter image description here"></a></p>

<p>The photos above was taken at the <a href="https://en.wikipedia.org/wiki/Porto_Alegre" rel="noreferrer">Porto Alegre</a> city, Brazil. (Coordinates: <a href="https://www.google.com/maps/place/30%C2%B001&#39;59.0&quot;S+51%C2%B013&#39;48.0&quot;W" rel="noreferrer">30°01′59″S 51°13′48″W</a>)</p>

<p>What are these fractal-like patterns? How and when are they formed? Is it some kind of organic formation? Is it living being or some kind of fossil?</p>

CC BY-SA 4.0
2019-11-21T21:04:04.270Z
Is that sloped at angle? Is it a street curb/gutter? What is the dividing line that cuts through the pattern? How old is the stonework. Location, climate?
Keith McClary
CC BY-SA 4.0
2019-11-21T21:10:40.920Z
https://www.sandatlas.org/dendritic-growth-in-crystals/
Keith McClary
CC BY-SA 4.0
2019-11-22T02:56:09.220Z
Dendrites , gradual crystal growth as the molten rock freezes. very similar to  patterns in as cast metals.
blacksmith37
<rocks><fossils><igneous>
Curious natural patterns on the surface of basalt blocks that make up the sidewalk
Lacobus
# Curious natural patterns on the surface of basalt blocks that make up the sidewalk

(Asked by: username_0 on 2019-11-21)

During one of my walks through the city streets, I noticed that some basalt blocks that make up the sidewalk have in their surface some very curious natural patterns:

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

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

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

[![enter image description here](https://i.sstatic.net/1lnff.jpg)](https://i.sstatic.net/1lnff.jpg)

The photos above was taken at the [Porto Alegre](https://en.wikipedia.org/wiki/Porto_Alegre) city, Brazil. (Coordinates: [30°01′59″S 51°13′48″W](https://www.google.com/maps/place/30%C2%B001'59.0"S+51%C2%B013'48.0"W))

What are these fractal-like patterns? How and when are they formed? Is it some kind of organic formation? Is it living being or some kind of fossil?

**Tags:** rocks, fossils, igneous

> **Comments:**
> **username_1**: Is that sloped at angle? Is it a street curb/gutter? What is the dividing line that cuts through the pattern? How old is the stonework. Location, climate?  
> **username_1**: https://www.sandatlas.org/dendritic-growth-in-crystals/  
> **username_2**: Dendrites , gradual crystal growth as the molten rock freezes. very similar to  patterns in as cast metals.  

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## 2 answers

### Answer by username_3 on 2019-11-22. Score: 7 | Accepted answer

These are most likely manganese dendrites. It is not a fossil, and not organic. These usually form in cracks in rocks, and most likely this slab was broken along an existing crack.

You can read more about it now: <https://www.mindat.org/min-26645.html>

One comment: this is not basalt. Basalt is black. Most likely some form of limestone.


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### Answer by username_4 on 2019-11-21. Score: 1

They are quite pretty, but they are not fossils. They remind me of the patterns that frost sometimes makes on window panes. A similar process is at work here, though with mineral bearing water infiltration rather than frost being the cause. The water infiltration deposits crystals in the rock.


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