Introduction

There are numerous silicate- and calcium-carbonate-based biominerals in biological systems. Their function is, for most of them, protection. They provide a hard shell beneath which the softer organism can survive and prosper.

Exceptions are the sponges. We will provide illustrative examples and describe the structure-mechanical property relations for a few representative examples. We first cover the most important silicates and then move to shells. The number of different species is staggering: over 100 000 living species bear a shell, ranging from a single valve to eight overlapping valves. There are roughly 1000 species of mussel bivalves.

For shells, we rely here primarily on the ones studied by the UC San Diego group: abalone, conch, giant clam, and ocean and river bivalve clams. They possess quite different and unique structures, and are representative of the large number of shell species.

We also describe other carbonate-based hard materials such as the sea urchin, the smashing arm of the mantid shrimp, and the ubiquitous egg shell.