title: Interdigitating biocalcite dendrites form a 3-D jigsaw structure in brachiopod shells.
abstract: We report a newly discovered dense microstructure of dendrite-like biocalcite that is formed by marine organisms. High spatial resolution electron backscatter diffraction (EBSD) was carried out under specific analytical conditions (15 and 10 kV) on the primary layer of the modern brachiopod Gryphus vitreus. The primary layer of modern brachiopods, previously termed nanocrystalline, is formed by an array of concave/convex calcite grains with interdigitated recesses and protrusions of abutting crystals without any cavities in or between the dendrites. The interface topology of this structure ranges from a few tens of nanometres to tens of micrometres, giving a nanoscale structure to the material fabric. The dendritic grains show a spread of crystallographic orientation of several degrees and can thus be referred to as mesocrystals. Individual dendritic mesocrystals reach sizes in one dimension larger than 20 μm. The preferred crystallographic orientation is similar in the primary and adjacent fibrous shell layers, even though these two layers show completely different crystal morphologies and grain boundary topologies. This observation indicates that two separate control mechanisms are active when the primary and the fibrous shell layers are formed. We propose a growth model for the interdigitated dendritic calcite grain structure based on a precursor of vesicles filled with amorphous calcium carbonate (ACC).
authors.affiliation: Department für Geo-und Umweltwissenschaften, LMU, München, Germany. andreas.goetz@lrz.uni-muenchen.de
authors.forename: Andreas J
authors.initials: AJ
authors.lastname: Goetz
authors.forename: David R
authors.initials: DR
authors.lastname: Steinmetz
authors.forename: Erika
authors.initials: E
authors.lastname: Griesshaber
authors.forename: Stefan
authors.initials: S
authors.lastname: Zaefferer
authors.forename: Dierk
authors.initials: D
authors.lastname: Raabe
authors.forename: Klemens
authors.initials: K
authors.lastname: Kelm
authors.forename: Stephan
authors.initials: S
authors.lastname: Irsen
authors.forename: Angelika
authors.initials: A
authors.lastname: Sehrbrock
authors.forename: Wolfgang W
authors.initials: WW
authors.lastname: Schmahl
mesh_terms: D000825:Animal Structures / Q000737:chemistry* / Q000648:ultrastructure; D000818:Animals; D002119:Calcium Carbonate / Q000737:chemistry*; D050091:Dendrimers / Q000737:chemistry*; D004583:Electrons; D007448:Invertebrates / Q000737:chemistry* / Q000648:ultrastructure
chemical_list: D050091:Dendrimers; D002119:Calcium Carbonate