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When,
at the beginning, the earth was covered only by water, billions of
cubic metres of salt were dissolved in these primitive seas together
with other minerals. Sea water has therefore been salty ever since the
formation of the primeval ocean, created by the condensation of the
steam contained in the primitive atmosphere.
Today, the oceans, which
cover close to three quarters of the globe, have an average estimated
depth of 3,500 to 4,000 metres. Each square metre is thought to contain
about one hundred tons of salt. An inexhaustible reserve for the world ...
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Salt
is found widely in nature. It is one of the most abundant minerals on
earth. It is found, as we have seen, in solution in sea water (about 35
g per litre). Indeed, all salt found on earth comes initially from the
sea.
Salt
is also found in many rivers, lakes and inland seas. For example, its
concentration varies from 0.002% in the water of the Mississippi to 30%
in the Dead Sea. Salt can form a layer or crust in swamps and on the
bottom of dried lakes, in particular in very arid regions. It is
constantly being formed by the action of streams and rivers on rocks
containing chlorides and sodium compounds.
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For
many centuries, the dwellers of salt marches have been providing salt,
produced by the evaporation of sea water in basins fed by channels. As
far as sea salt is concerned, the white salt comes mainly from the
Mediterranean and the grey salt from the Atlantic and from two salt
marches at Noirmoutier and Guérande.
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The
mineral halite, better known as rock salt, is formed by the dehydration
of former areas of salt water. Later, the beds thus formed were often
buried under other sedimentary deposits. Halite beds have a thickness
that varies on average from 2 to 30 m, and it has been found at
impressive depths.
This mineral is often found in association with gypsum, sylvite, anhydrite, calcite, clay and sand.
Halite
is very common throughout the world. In Europe, it is found notably in
Poland, in Germany and in France (mines and salt marches).
It is
colourless and transparent when pure, but it is often tinted with
yellow, red, blue or purple by the presence of impurities.
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Bibliography
'Mines et Salines Vaudoises de Bex au point de vue historique, technique et administratif',
par Ed. Payot. 1921
'Essai sur la Montagne salifère du gouvernement d'Aigle', par François Sam. Wild. 1788
'Mines de sel de Bex, aperçu géologique et minier', par H. Badoux. Editeur: Aminsel. 1982.
'La Fabuleuse histoire du sel', par André Besson, Editions Cabédita, collection Archives vivantes. 1998.
Documentation 'Jura-Sel, authentique depuis 200 millions d'années'. Salines du Rhin Suisse. 1997.
'Nous avons partagé le pain et le sel', par Serge de Beaurecueil. Editions du Cerf. 1965.
'Les Mines et Salines de Bex, une grande aventure humaine'. Ouvrage collectif.
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