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Stone patterns
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Stone patterns

This photo was taken April 2010 it is exposed stone in a burn in Evie, I would be interested to know how the patterns came to be ?
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Picture added on 30 April 2010 at 17:58
Comments:
In geological terms it is dried mud.
Added by Neil Johnstone on 30 April 2010
These are sun cracks Alan, some 350 million years old! They formed as a result of the drying out of muddy puddles on lake shores, just as they do today. The cracks were later infilled by sand giving this polygonal network, the underlying mud hardened into mudstone, a dark grey crumbly rock.
Added by Max Fletcher on 01 May 2010
... former mudcracks ... later on filled with different material and then petrified
see also:
en.wikipedia.org/wiki/Mudcrack
... indicating times of climatic changes during the times of Lake Orcadie
see also here:
www.fettes.com/orkney/Fossils/index.htm

Mudcracks (drier era) next to Ripple Marks (wetter era), the second feature which ist quite common with Orkney rocks
Added by Wolfgang on 03 May 2010
Thanks all for your replies, it's very interesting.
Added by Alan on 03 May 2010
I seem to remember being told that this formation was called tessellated pavement, when I was a member of the Junior Field Club (approximately 30 years ago, I'm afraid to say!). That's long enough ago that I might even be wrong... not that I'm going to admit to that!!
Added by Graham Garson on 03 May 2010
Can't say for sure but I'd guess they are fossilized (petrified) mud cracks. The ridges represent sandstone that has cemented more than the rest of the rock and is thus harder to erode. Possibly the cracks in the mud filled with some material that would then cement more effectively either as part of sedimentation or possibly after burial where the cracks represented conduits for ground water to flow. If that contained calcite or clay then anything left behind would cement. You often get this kind of hehaviour in fractures but the almost hexagonal nature of the shapes suggests what you get when mud dries and cracks. Certainly there are newer fractures which have eroded more effectively indicating processes at different time scales and the ridges cross those fractures. That's all a guess though.
Here are some pictures of mud cracks that have been preserved, either without cementation or with.
geology.about.com/od/geoprocesses/ig/sedstrucs/mudcracks.htm
www.t-rat.com/Pages/TheMoenkopiFormation.html
picpoke.com/im/20f8dx

See the "hand beast" picture on the last one.

Added by Karl Stephen on 04 May 2010
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