Limestone is a type of pale rock mainly made from the remains of tiny sea creatures and shells pressed together over millions of years. It is often used as a building material and to make cement.
The word joins “lime,” referring to calcium compounds, and “stone,” meaning rock. It appeared in English in the late Middle Ages to describe rock that could be burned to make quicklime.
Many limestone rocks are basically ancient seas turned into stone, full of microscopic fossils. When you walk past a limestone building, you’re literally walking past compressed ocean life from ages long before humans existed.
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