Septary

Septarie from North Africa

Septary, bevel. Canadian Museum of Nature, Ottawa

Septarie is a geological term . Derived from the Latin s (a) eptum (= partition), it denotes lime concretions in calcareous clays of sometimes considerable size. In their interior they are criss-crossed by radial cracks (drying-out shrinkage cracks). Often minerals such as calcite are deposited in these cracks (formation of septa), but other filling minerals (e.g. siderite , pyrite , barite or quartz ) may also be present. In the center of septaries there is very often a nucleus made of originally organic material.

Emergence

According to F. Lippmann (1955) the formation of septaries goes back to the decomposition of organisms. Accordingly, the decomposition of organic material leads to the formation of ammonia and amines , which lead to an increase in the pH value in the surrounding sediment . This reduces the solubility of carbonates , which leads to the migration and deposition of carbonates on the fossil . In this way, there is an undersaturation of carbonates in the surrounding sediment, which in turn leads to the migration of more and more carbonate pore water solutions . So septaries can continue to enlarge until the decomposition of the organic material, i.e. the formation of ammonia, has ended or the supply of lime dries up.

Occurrence

Septaries can be found worldwide and are usually found in carbonate-rich slates . A layer deposited in the middle Oligocene , the Septarian clay , was given this name because of the regular occurrence of Septaria.

use

Septariums are mainly used for handicrafts. Due to their often attractive pattern, large copies are made into table tops or bookends, for example, while smaller ones are made into brooches.

gallery

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  Septarie from the Rupel of the Amsdorf opencast mine

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  Septary. Bristol City Museum

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  Moeraki Boulders in New Zealand

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  Septarie from Muddy Creek , Utah

literature

• Georg Wagner : Introduction to the history of the earth and landscape . Publishing house d. Hohenloheschen Buchhandlung F. Rau, Öhringen 1931, DNB 561012482 .

Web links

Commons : Septarie  - collection of images, videos and audio files

• Irna, 2006, image collection of spherical septaries worldwide
• Information from mineralienatlas.de
• Information on GemRocks (English).

Individual evidence

1. ↑ ^{a b} H. Murawski, W. Meyer: Geological dictionary. 11th edition. Spectrum Academic Publishing House, 2004, ISBN 3-8274-1445-8 .
2. ↑ Collective of authors: Lexicon of Geosciences , Volume III, Spektrum Akademischer Verlag, Heidelberg, Berlin 2000, ISBN 3-8274-0422-3 , p. 152