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The Loire Valley formed the floor of a vast sea 90 million years ago. Over the millennia, sediment from the sea floor, comprising fossilized living organisms and sand particles, became compressed to form what is now known as Tuffeau stone.
Mining of Tuffeau stone for construction reached its peak in the 15th century, and the mining techniques used to extract the valued stone created a vast network of caves in the Loire Valley. The caves have been used as dwellings in the past, partly due to the practicality that the indoor temperature is remarkably constant from summer to winter.
Many of the larger caves are used for growing a wide variety of mushrooms, which are transported daily to the markets in Paris.
A number of buildings in the valley were built from large blocks of Tuffeau stone, including the Château de Beaulieu near Saumur, the Château d'Ussé and the Château de la Motte d'Usseau, and many worker's cottages at Longères.
Tuffeau has a very low density compared with many other rocks, being half as dense as granite, comparable in density with ebony, and only about 10 to 20% heavier than water. Tuffeau has porosity of up to 50%, whereas that of granite is only about 1%. The compressive strength of the stone is a factor of ten to twenty times less than that of granite.
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