What are sea urchins' spines made from?

As with many structural biological materials in marine environments – those of coral reefs and mollusc shells, for example – sea urchin spines are composed of calcium carbonate. In its basic state, this is a rather brittle mineral – think chalk – but evolution has come up with a variety of ways to strengthen it.

When found in nacre (mother of pearl), it is laid down as multiple layers of thin sheets, an arrangement that prevents fractures from spreading.

When found in sea urchin spines, microscopic blocks of the mineral
are cemented together.

This design is inspiring human engineers to develop super-tough, concrete-like materials that, in theory at least, could support structures eight kilometres high – ten times the height of the world’s tallest building.

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