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Hi Sir. I am a student of BS Geology. My question is " why mud cracks are polygonal in shape ?

Hi Nisar,
Interesting question.  

As mud (actually, most sediments really) dries out the water is removed, resulting in a loss of volume in the sediment.  The surface tries to shrink more quickly because the interior is wetter.  This causes a strain to develop in the top layer.  When the strain gets high enough a crack develops in the desiccated surface, which relieves the strain.  

Individual cracks will lengthen and, since the surface desiccation is in every direction, other cracks will propagate in different directions.  All the cracks will spread and join with other cracks forming polygons.

Experiments show cracks with 90 degrees are preferentially generated, but repeated wetting and drying will create angles of 120 degrees, forming hexagons.  Another interesting problem is, "Why hexagons".  Turns out that hexagons are preferentially created in nature since they constitute a form that uses space most efficiently.  It can be shown mathematically (more than I need to know) in "Mathematics in Nature: Modeling Patterns in the Natural World"
By John A. Adam.

Check out this paper;

It will tell you a lot more about mudcracks.

Hope this helps.


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C. Robert Reszka, Jr.


I can answer any general geology question (rocks, minerals, stratigraphy, geomorphology etc.). My expertise is in the geology of the Michigan Basin, PreCambrian, Paleozoic and Recent. I can answer questions concerning mining and petroleum exploration and production and the laws concerning those activities. I can also answer questions concerning stratigraphy of the Michigan Basin. I will also answer questions about mineral and rock collecting in the Basin. I won`t be able to answer many specific questions on hydrology, geophysics or geochemistry. I may be able to answer very general questions in those venues.


I have been working for the State of Michigan for 36 years as a Geologist and a Resource Analyst. I have experience with Subsurface Geology and Petroleum Geology, mining in Michigan, and Sand Dune Mining and Protection issues.

Michigan Basin Geological Society

Decade of North American Geology.
Bedrock Geology of Michigan

BS Wayne State University

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