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| Limestone rock | |
 Tuffeau from theTuronian atLa Chapelle-Huon |
Tuffeau stone — inFrench, simplytuffeau ortufeau — is a locallimestone of theLoire Valley ofFrance. It is characterized as a chalky or sandy, fine-grained limestone, white to yellowish-cream in appearance, and micaceous (containing some white flakes ofmica, ormuscovite). The soft stone is extracted from numerous quarries and has made a major mark on the architectural landscape of the Loire and its tributaries — especially the valley'schateaux.[1]
Thetuffeau formed in theMesozoic era (in theTuronian stage of theUpper Cretaceous). The Loire Valley, at that time, was on the seabed; over the millennia, the sediments that deposited on the bottom, consisting of fossilized living organisms and sand particles, under the effect of pressure underwent crystallization and cementation and formed thetuffeau.[2] It differs fromchalk by the presence ofForaminifera and many shell remains deposited in shallow waters, between 2 and 20 meters, and subsequently agitated, as occurs near the shoreline. In contrast, true Chalk is rich in another type of shell microfossil, thecoccolith, due to sediment deposition in deeper and calmer waters (about 200 meters deep).[3]
There are several varieties oftuffeau: whitetuffeau, the noblest variety, used for the construction of prestigious buildings; yellowtuffeau, more sandy, used in Touraine for the construction of rural buildings; graytuffeau, with bluish reflections, used in the production of hydraulic lime.[4][5][6] Tuffeau has a very low density of 1.3 g/cm3. It has a porosity that reaches 45%; compressive strength is also very low (10 MPa).[7][5][6]
The termtuffeau is etymologically linked totuff, to which it is not geologically related (the latter is of volcanic origin), and totufa, similar totravertine, to which it is instead geologically similar.[3] All these terms derive from the Latintōphus ortōfus ("stone").
Tuffeau has a very low density compared with many other rocks, being half as dense as granite, comparable in density withebony, and only about 10 to 20% heavier than water. It has porosity of up to 50%, whereas that of granite is only about 1%. The compressive strength of the stone is a factor of 10 to 20 times less than that of granite.[5][6]
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The extraction oftuffeau, which began already in the Gallo-Roman period, reached its peak in the 15th century, when, especially inTouraine andAnjou, it was extracted from the natural cliffs overlooking the rivers, mainly the Loire, thanks to which the building blocks were transported on boats.[8] Over the centuries, the extraction of material created vast underground galleries, some of which several kilometers long. These artificial caves, today calledles troglodytes and concentrated especially aroundSaumur, were long used as dwellings thanks to the constant internal temperature throughout the year.[5][6]
Currently, the quarries are largely used as cellars, while some host mushroom cultivation;tuffeau, after being abandoned around 1950, resumed being extracted in the 1960s, mainly for the restoration of historic buildings.[4][8][2]
In the Loire Valley, numerous buildings, public and private, are built intuffeau, thanks to the ease of working with this material, which allows for elaborate geometries for friezes, pilasters, and capitals.[4] Among the monuments built with this material are the Château de Beaulieu nearSaumur, theChâteau d'Ussé and the Château de la Motte d'Usseau, many worker's cottages at Longères, theNantes Cathedral and many of the châteaux of the Loire, including those ofChambord,[9]Chinon,Azay-le-Rideau, andVillandry.[4]
Being a soft stone, however,tuffeau is subject to rapid erosion by scaling or chipping, accelerated by weather conditions (humidity, temperature excursion) or environmental (presence of pollutants). For this reason, the stones must be constantly replaced with othertuffeau or with more resistant material.[5][6][10]
