Calcite morphology, texture and hardness in the distinct layers of rhynchonelliform brachiopod shells

Hierarchical structure of marine shell biomaterials: biomechanical functionalization of calcite by brachiopods

“…Figure 3 shows EBSD maps of the columnar layer of Liothyrella neozelanica (Goetz et al, 2009). From the contact zone of the columnar layer and the primary layer towards the inside of the shell the column width increases and the axial crystallographic preferred orientation becomes increasingly sharp; it even reaches a three-dimensional single-crystal-like texture ( Fig.…”

“…3). For Liothyrella neozelanica (Goetz et al, 2009) the columnar layer follows inward below the primary layer, and the fibrous and the columnar layer change their thickness along the length of the valve in a wedge-like manner as one layer replaces the other essentially preserving the thickness of the valve. Occasional interlayering of fibrous material into columnar material can be observed in L. neozelanica (Goetz et al, 2009).…”

“…5a and 6a shows that the primary layer is differentiated into sub-layers, where usually nanostructured material is on the outside, while micrometer-sized columnar or platelet-shaped crystals form a sub-layer towards the inward of the valve (e.g. Schmahl et al 2008;Goetz et al 2009). The large and mineralogically inconspicuous calcite columns (Fig.…”

Mechanical properties of modern calcite- (Mergerlia truncata) and phosphate-shelled brachiopods (Discradisca stella and Lingula anatina) determined by nanoindentation

“…This is achieved by the organic matrix in the composite that provides flexibility and cohesive strength. The calcitic terebratulide shell structure is layered, with a nanocrystalline outer, primary layer, and a fiber-composite secondary layer (some species show a tertiary layer of columnar calcite, Goetz et al, 2009, which is not present here). The secondary layer is composed of sub-layers with distinct morphological directions of the fibers.…”

“…Within the hierarchical organization each level contributes to the overall function of the resulting biomaterial and thus influences the mechanical properties of the final product (e.g., Okumura and De Gennes, 2001;Currey, 2005;Rousseau et al, 2005;Miserez et al 2008). As shown for bivalve (Kamat et al, 2000) and brachiopod shells (Schmahl et al, 2004(Schmahl et al, , 2008Griesshaber et al, 2006Griesshaber et al, , 2007Goetz et al, 2009) the microstructure is of profound importance for the shell's mechanical properties since these change as a function of dimension. For example, the smaller a crystallite becomes the less important is the weakening influence of defects (Ji et al, 2004).…”