Figure 4: HAADF-STEM images of nacre formation viewed from orthogonal directions.
Early formation begins with the appearance of CaCO3 layers with planar disk geometry (>1 μm diameter, ∼300 nm thick), after which nano-aggregation of ∼60 nm crystals of aragonite accumulate along the growth direction with increasing density. Once a critical packing density is reached, early-nacre platelets form as a packed continuum with adjacent nanocrystals. Nacre plates are separated by a thin (∼8 nm) organic sheet. Eventually, uniform ordered nacre platelets are formed. Organic spheroid inclusions can be seen in nacre. Scale bar, 200 nm.
