Mollusc Shell (eroded)

This mollusc shell is highly eroded, revealing some of the secrets of its structure. Shells, like all hard structures in animals, are formed in the organism by a process called biomineralisation. Minerals produced in the organism are fused with soft biological tissues to make the very strong composite materials which comprise teeth, claws, bones and many more structures. Mollusc shells are around 95% calcium carbonate, which is why this weathered shell has a very chalky appearance – the erosion has removed the protective outer layer revealed the inner composition.

This shell is half of a hinged two-shell set which would have housed a bivalve mollusc. The shell is in fact the mollusc’s skeleton. Instead of having an internal skeleton on which their flesh hangs, many animals have an ‘exoskeleton’ which contains and supports the animal’s organs and tissues inside. Other examples include crabs, grasshoppers and cockroaches.

Mollusc shells exhibit some very interesting mechanical properties, and for this reason are studied by material scientists. For example, the fracture toughness of a mollusc shell is dramatically higher than the fracture toughness of the individual crystals that it is made from, meaning its toughness is derived from the very specific way that the composite forms.