3 research outputs found
Interdigitating biocalcite dendrites form a 3-D jigsaw structure in brachiopod shells
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 lm. 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)