Beautiful natural materials

Have you ever walked on a sandy beach with your head constantly looking down in search of colorful seashells? It is something I like to do every time I have a chance. Seashells come in different colors and shapes, and I am always amazed not only by their beauty but also by their structure.

Some are smooth and porcelain-like. Others have ridges, delicate patterns or a beautiful pearly sheen. Pick one up and there is suddenly much more to see. So what exactly are we looking at?

A seashell is primarily made of calcium carbonate, the same mineral found in materials such as limestone and marble. Depending on the species, it occurs mainly as calcite or aragonite. And there is more! Small amounts of proteins and other organic compounds help control how the mineral crystals form and how they are arranged. This combination of mineral and organic material gives shells some of their distinctive properties.

The result is a natural composite material, produced by a living animal.

And how about the shiny inside of abalone? This is nacre, often called mother-of-pearl.

Under magnification, nacre reveals a beautiful layered structure. Tiny tablets of aragonite are stacked in layers, separated by thin organic interfaces. This structure helps make nacre both hard and remarkably tough. When a crack moves through the material, the layered architecture can interrupt and redirect it, making the crack harder to propagate. The same structure also creates its characteristic glow. Light interacts with the very thin layers within the nacre, producing interference effects that can make pinks, greens, blues and golds appear to shift as you move the shell.

Shells in fashion

Perhaps this is one reason shells have fascinated us for so long.

Humans have used shells as adornment for thousands of years until today. They have been made into beads, pendants, buttons and decorative objects.

We can find shell and mother-of-pearl incorporated into earrings, necklaces, bracelets, buttons and accessories. Designers often leave the material relatively simple, allowing its natural colour and iridescence to provide the decoration.

Beauty built through growth

The shell’s shape is part of its story too.

As the mollusk grows, it adds new material to the shell. Ridges, bands and changes in colour can develop along the way, creating the patterns we see on the finished object.What we pick up on the beach is therefore the result of a long process of biological growth. The shell has its own chemistry, its own structure and its own history. That is what makes it such an interesting material to look at.

We often think of materials as things humans manufacture: glass, metal, silk, ceramics. A seashell reminds us that some of the most extraordinary materials are made by living organisms.

Look closer

Next time you find a shell on the beach, turn it over in your hand.

Look at the ridges. Hold the inside towards the light. Notice how the colour changes as you move it. Think about the layers of mineral and organic material that make up its structure, and the living animal that produced them.

A seashell can be beautiful from a distance. Look closely, and it becomes a material worth studying.

Further reading

Few references for readers who want to explore the science behind shells and nacre:

• “The Dynamics of Nacre Self-Assembly” looks at how the layered structure of nacre develops.
• “A Bivalve Biomineralization Toolbox” explores the biological and molecular processes involved in shell formation.
• “The Toughening Mechanism of Nacre and Structural Materials Inspired by Nacre” examines the structure responsible for nacre’s remarkable toughness.
• “Bioinspired Materials: From Living Systems to New Concepts in Materials Chemistry” discusses biomineralization and the chemistry behind natural mineral formation.