Fig. 2

Eggshell ultrastructure and microstructure. a Scanning electron microscopy (SEM) image of an eggshell at an early stage of calcification (6 h post-ovulation.), showing aggregates of calcite crystals on mammillary knobs and ACC (amorphous calcium carbonate) flat-disk shaped particles on the shell membranes. b SEM image of cross-fractured eggshell showing the palisade layer (PL), mammillary layer (ML) and shell membranes (SM). Optical microscopy images of an eggshell cross-section: c as viewed under cross-polarized illumination, showing the columnar calcite crystal units of the mineral. d View under parallel light showing the distribution of the internal organic matter within the mineral. Scale bars are: a 10 μm; b 100 μm; c and d 200 μm