limestone
limestone
English (Old English)
“Limestone is the only common rock named for its use rather than its origin — the Anglo-Saxons called it 'lime-stone' because they burned it to make lime for mortar.”
Limestone is a compound of lime (from Old English līm, meaning a sticky substance or cement) and stone. The word is Anglo-Saxon and practical: the stone that produces lime when heated. Lime — calcium oxide — is made by burning limestone (calcium carbonate) in a kiln. The resulting quickite reacts with water to form slaked lime, which hardens into morite when mixed with sand. This chemistry has been known for at least 10,000 years. Göbekli Tepe, built around 9500 BCE, used lime mortar.
Limestone is one of the most common sedimentary rocks on Earth. It is formed primarily from the accumulated shells, skeletons, and fragments of marine organisms — coral, foraminifera, mollusks — compressed over millions of years. The White Cliffs of Dover are chalk, a soft form of limestone made almost entirely from microscopic coccoliths (the calcium carbonate plates of single-celled algae). The rock is biological in origin. Limestone is the graveyard of the ocean.
The great limestone buildings of civilization — the pyramids of Giza, the Parthenon, the medieval cathedrals — are all built from compressed sea life. The Pyramids of Giza, constructed around 2560 BCE, are made of nummulitic limestone — rock formed from the shells of coin-shaped foraminifera. Each block contains millions of fossil organisms. A pyramid is a fossil monument.
Limestone is also the raw material for cement, the most widely used building material in the world. Portland cement, patented by Joseph Aspdin in 1824, is made by heating limestone with clay. Concrete — cement mixed with sand and gravel — is the second most consumed substance on Earth, after water. The humble lime-stone of the Anglo-Saxons now holds up the modern world.
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Today
Concrete production — which requires limestone — accounts for about 8 percent of global CO2 emissions. Burning limestone releases the carbon dioxide that marine organisms captured millions of years ago. The fossil graveyard gives back its carbon. The material that built the modern world is one of the largest contributors to its warming.
The Anglo-Saxon compound has not needed updating. Limestone is still the stone that makes lime. The chemistry has not changed. The scale has. A word for a kiln-stone now names the raw material of civilization — and one of its central environmental problems.
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