Abstract
Applying the theories of Materials Science and Engineering to describe the composition and hierarchy of microstructures that comprise biological systems could help the search for new materials and results in a deeper insight into evolutionary processes. The layered microstructure that makes up the freshwater bivalve Limnoperna fortunei shell, an invasive specie in Brazil, was investigated utilizing SEM and AFM for the determination of the morphology and organization of the layers; and XRD was used to determine the crystalline phases of the calcium carbonate (CaCO3) present in the shell. The presence of the polymorphs calcite and aragonite were confirmed and the calcite is present only on the external side of the shell. The shell of L. fortunei is composed of two layers of aragonite with distinct microstructures (the aragonite prismatic layer and the aragonite sheet nacreous layer) and the periostracum (a protein layer that covers and protects the ceramic part of the shell). A new morphology of the calcite layer was found, below the periostracum, without defined form, albeit crystalline.
Highlights
CaCO is the second most abundant mineral existing 3 in the earth’s crust, exceeded only by quartz
The objective of this study was to characterize the microstructures and to determine the calcium carbonate phases present in the shell of L. fortunei to help to understand the processes involved in the formation of the shell, aiming to promote the creation of new controlling methods this invasive specie
The shells were kept separately so that the shells of the same animal were not analyzed by the same technique and distributed as follow: Seven (7) shells were destined to scanning electron microscope used (SEM) analysis, two (2) shells to Atomic Force Microscopy (AFM) and five (5) shell to XRD
Summary
CaCO is the second most abundant mineral existing 3 in the earth’s crust, exceeded only by quartz. Crystalline CaCO occurs in three forms: calcite, aragonite and vaterite. CaCO3 occurs in amorphous phase (ACC – amorphous calcium carbonate). Calcite is the most abundant, crystallizes according to the triclinic system and possesses a density of 2.71g/cm[3]. Bridgman was the first to show that calcite has high-density polymorphic forms[1]. Much less abundant than calcite is aragonite, an orthorhombic polymorph having a density of 2.93g/cm[3]. The third polymorph is vaterite, hexagonal and with a density of 2.54g/cm[3]. Aragonite and vaterite are metastable at normal ambient temperatures[2]
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