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Geology/calcite conical structures


discoidal structure
discoidal structure  

discoidal structure
discoidal structure  
I found in Cretaceus argillitic shales, a lot of these flat conical structures in fibrous calcite. (nothing to do with "cone in cone" structures). The ridges are only on the external surface.
In the layers (marine sediments) there are no fossils.
I have not found anything similar in literature.
Till now, nobody has been able to tell me what it could be.
Thank you in advance.


Sorry for the delay in response.  These are great pictures and a great description of what you have found.  I THINK (am not positive) that these might be some mineralogical phenomena.  I have seen in shales - much older - large concretions.  These concretions, sometimes a meter across and half that high, seem to start growing around some tiny concentration of some mineral (a calcium crystal for instance).  In this instance, given the age your describe (K) it is possible to imagine some volcanic fallout providing the catylst for this growth.

The ridge structure that you have documented also looks remarkably like a pseudomorph after gypsum. However, if this is really an argillite that seems unlikely as we would need some period of exposure to the sun to cause this to happen.

I would be curious to see a stratigraphic column describing the vertical distribution of these features along with any other features observed in the shale..........




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Fraser Hamilton


I have over 15 years of professional experience in the environmental geology field. I am well versed in general geology types of questions and answers. In addition I have a keen understanding of physical stratigraphy (especially in the Valley and Ridge of Central PA) and cycles.


Eight years of education, fifteen years of professional experience. Have worked or studied in ME, PA, TX, KY, IN, TN, OH, WA and Scotland.

Geological Society of America
American Association of Petroleum Geologists
Properties Magazine
Cleveland Bar Association
Cleveland Engineering Society

BA Geology/Math, University of Maine at Farmington
MA Geology - Physical Stratigraphy, Temple University
Post Grad Studies Geology - Texas A&M University

Awards and Honors
Distinguished graduate teaching award, Temple University

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