Goetz, Andreas J.; Steinmetz, David R.; Griesshaber, Erika; Zaefferer, Stefan; Raabe, Dierk; Kelm, Klemens; Irsen, Stephan; Sehrbrock, Angelika; Schmahl, Wolfgang W.
Interdigitating biocalcite dendrites form a 3-D jigsaw structure in brachiopod shells.
In: Acta Biomaterialia, Vol. 7, No. 5: pp. 2237-2243
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We report a newly discovered dense microstructure of dendrite-likebiocalcite that is formed by marine organisms. High spatial resolutionelectron backscatter diffraction (EBSD) was carried out under specificanalytical conditions (15 and 10 kV) on the primary layer of the modernbrachiopod Gryphus vitreus The primary layer of modern brachiopods.previously termed nanocrystalline, is formed by an array ofconcave/convex calcite grains with interdigitated recesses andprotrusions of abutting crystals without any cavities in or between thedendrites The interface topology of this structure ranges from a fewtens of nanometres to tens of micrometres, giving a nanoscale structureto the material fabric The dendritic grains show a spread ofcrystallographic orientation of several degrees and can thus be referredto as mesocrystals. Individual dendritic mesocrystals reach sizes in onedimension larger than 20 mu m The preferred crystallographic orientationis similar in the primary and adjacent fibrous shell layers, even thoughthese two layers show completely different crystal morphologies andgrain boundary topologies. This observation indicates that two separatecontrol mechanisms are active when the primary and the fibrous shelllayers are formed We propose a growth model for the interdigitateddendritic calcite grain structure based on a precursor of vesiclesfilled with amorphous calcium carbonate (ACC).