During the Tertiary period, the alternative extension of lands and seas beyond the Paris Basin, concentration and evaporation of sea water in a hot and dry climate, allowed the precipitation of salts in the water under as small or large gypsum crystals.
The mineral and deposited in a layer of water film has preserved skeletal remains of large mammals such heavy herbivore Paleotherium who frequented the banks of the lagoon of the time.
These gypsum deposits (hydrated calcium sulfate natural (CaSO4-2H2O) usually called "plaster stone") are very present:
In Seine-Saint-Denis in the Val-de-Marne: Romainville, Vaujours, Gagny
In the Val-de-Marne: Neuilly-sur-Marne
In the Yvelines at Vaux-sur-Seine
In the Val-d'Oise Argenteuil, Cormeilles-en-Parisis, on the hill of Hautil and Grisy-les-Plâtres which roughly marks the western boundary of deposits.
These deposits, formed in the evaporite basin in the Paris region between 37 and 33 million years represent 70% of reserves.
Sedimentary rock, colorless, white, yellow, gray, pink, brown, black .., natural gypsum quarry is extracted in open pit or underground galleries.
The plaster stone
Gypsum that undergoes slow cooking and moderate between 150 and 200 ° giving a powdery product after grinding. With a water intake this turns into paste and hardens quickly to give the plaster ... "rice powder" that women use for their makeup.
Known Egyptians, Cretans, Greeks, use of gypsum Gaulle for making plaster dates back to Roman times or plaster of Lutetia was renowned for its finesse and plastic quality.
In the Merovingian, it was widely used for making sarcophagi molded decorations. Copies are displayed in the museum of Guiry-en-Vexin.
In the Middle Ages, the plaster was widespread use, used as mortar or stucco, insofar a house plastered plaster better resisted the fire, as feared at the time.
According to the website of the municipality of Grisy les Platres
Determination of criteria
Gypsum is slightly soluble in pure water, a maximum solubility of 2.5 g per liter in normal conditions of temperature and pressure. The solubility of gypsum per 100 g of pure water, only 0.223 g at 0 ° C (cold water) and 0.257 g at 50 ° C. The solubilization is more effective between 30 and 40 ° C. The passage in solution or dissolution is generally imperceptible to the eye. The water that has dissolved gypsum was named by the ancient chemists selenitic water, or once "Moon Water" in the medieval tradition of plasterers. This selenitic water is unsuitable for cooking food and soaping linen. It was formerly hated by the washerwomen or housewives or cooks, but also by blacksmiths and stonemasons as gypsum or the compounds of the family of calcium sulphate, calcium sulphate, gypsum, mirabilite ... more or less soluble or worn by dust after drying up promote rusting of iron, as earlier alteration stones.
According to Wikipedia
Question for this earthcache:
1- According to the panel (contact) that is the problem of water in Grisy plasters?
2- What phenomenon promotes this problem?
3 What is the name given to this water then?
4- Why the water was not appreciated blacksmiths and stonemasons?