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The Ultrastructure of Brachiopod Shells - A Mechanically Optimized Material with Hierarchical Architecture

Published online by Cambridge University Press:  26 February 2011

Erika Griesshaber
Affiliation:
erika.griesshaber@rub.de, University of Bochum, Geology, Mineralogy and Geophysics, Germany
Klemens Kelm
Affiliation:
kelm@uni-bonn.de, University of Bonn, Inorganic Chemistry, Germany
Angelika Sehrbrock
Affiliation:
sehrbrock@caesar.de, CAESAR, Germany
Reinhart Job
Affiliation:
reinhart.job@fernuni-hagen.de, University of Hagen, Electrical Engineering and Information Technology, Germany
Wolfgang W. Schmahl
Affiliation:
wolfgang.schmahl@lrz.uni-muenchen.de, University of Munich (LMU), Earth Sciences, Germany
Werner Mader
Affiliation:
mader@uni-bonn.de, University of Bonn, Inorganic Chemistry, Germany
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Abstract

Brachiopod shells consist of low-magnesium calcite and belong to one of the most intriguing species for studies of marine paleoenvironments, variations in oceanographic conditions and ocean chemistry [6, 7, 11 – 13]. We have investigated the ultrastructure together with nano- and microhardness properties of modern brachiopod shells with transmission electron microscopy (TEM), scanning electron microscopy (SEM), nanoindentation and Vickers microhardness analyses. Brachiopod shells are structured into several layers, a thin, outer, hard, protective primary layer composed of randomly oriented nanocrystalline calcite, which is followed inward towards the soft tissue of the animal by a much softer shell segment (secondary layer) built of long calcite fibres, stacked parallely into blocks. The hardness distribution pattern within the shells is non-uniform and varies on scales as small as a few tens of microns. Our results show that the hardness of this biomaterial is controlled by two predominant features: (1.) The morphological orientation of the calcite fibres (not by the crystallographic orientation of the fibres), and (2.) the amount and distribution pattern of organic material between and within the calcite crystals.

Type
Research Article
Copyright
Copyright © Materials Research Society 2006

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