calx

The Latin word calx meant 'limestone' or 'lime' — the calcium carbonate rock that Romans burned in kilns to make quicklime for mortar. Roman engineering ran on calcium. The Colosseum, the Pantheon, the aqueducts — all held together by lime morite. The word calx itself may trace back even further, to Greek khalix (χάλιξ), meaning 'pebble' or 'gravel,' the raw material before the kiln.

For two thousand years, nobody suspected that lime contained an undiscovered element. Lime was just lime — a useful substance, not a compound hiding a secret. In 1808, Humphry Davy (the same man who had isolated sodium and potassium the year before) passed electric current through a mixture of lime and mercuric oxide. A new metal appeared. Davy called it calcium, from calx. He was 30 years old and had now discovered five elements.

Calcium is the fifth most abundant element in the earth's crust. It is in chalk, marble, limestone, coral, eggshells, seashells, stalactites, and the hard water that leaves rings in your bathtub. The White Cliffs of Dover are calcium carbonate — the compressed skeletons of trillions of microscopic organisms called coccolithophores that lived and died in a Cretaceous sea 70 million years ago.

Your skeleton is a calcium structure. Your teeth are calcium phosphate. Every time a nerve fires or a muscle contracts, calcium ions are flowing. The element that Romans burned to build their empire is the same element that builds your bones. When a doctor tells you to take your calcium, they are prescribing limestone — the same substance the Romans heated in their kilns, renamed by the man who could not stop discovering elements.