Figure 5.4: Cloud layer
The figure shows the calcite layer, an irregular, hard polycrystalline layer with poorly defined morphology. This is a new microstructure in mollusc shells, called the “Calcite Cloud Layer” due to its resemblance to nimbus clouds. The major part of the golden mussel shell is formed with aragonite – a polymorph of CaCO3, orthorhombic, metastable at room temperature – that is microstructurally organized in the form of superimposed overlapping tile shapes, the nacre layer (≈ 120μm) and in the shape of prisms, the prismatic layer (≈ 26μm). On the contrary to other bivalves, in the species L. fortunei, the prismatic layer is located in the interal part of the shell and is composed of aragonite.
Figure 5.5: Detail of the transition of the calcite layer (C) and the nacre layer (N).
