Slate
The slate is a metamorphic Roche pertaining to the family of the Schistes. The slate is resistant and its color can vary white with the black, while passing by all kinds of gray, dark reds and greens. The slate can be right (rectangular) or in the shape of scale. Its thickness varies from 3 mm with 9 Misters Between 20 mm and 40 mm, it acts of Lauze, another more massive schist and less folded. The installation with old is the installation with the nail (more expensive because are needed bored slates), end XIXe appears the installation on hook (the slate is simply supported in foot).
Layers slaters in France
Legal status of the salte quarries
The mining code, bench in 1810, classified the salte quarries in the family of the careers (underground). Since 1946, the slaters are compared to the statute of minor.
Some historical reference marks
Formerly, the department of the the Ardennes also had important exploitations (Fumay, Haybes, Rimogne,…) who ceased all their activity at the end of the 20th century (1971). One finds also basins slaters in Brittany (salte quarries of Maël- Carhaix), in Corrèze (Allassac and Travassac), in the the Alps and the the Pyrenees.
Geographical distribution of the various basins
One finds slate in the following departments:
Currently, the most important layer in France is located on the territory of the town of Trélazé being next to Angers, in Maine-et-Loire. One produced there between 15 and: 20000 tons of slate per annum within two underground workings.
Some geochemical data on the salte quarry angevine
average Chemical composition of the slate angevine (according to Marty) :
Silica 50%, Alumina 30,1%, Iron Oxide 8%, Magnesia 2,3%, Mug up 3%, Soude 1,3%, Eau 3,3% and Divers 2%
The slate angevine was formed it there has 460 million years, with the ordovician and is resulting from the compacted oceanic clay transformation, little by little metamorphized out of very pure schist: it is the slate which we know.
Extraction and manufacture
The extraction can be carried out with open sky or in an underground way. Certain areas, Corrèze and Anjou, saw the two techniques coexisting. In others, as in the Ardennes, Savoy, it is or was exclusively underground. The independent factor which conditions the mode of extraction puts back on the Pendage vein.
Then, the blocks are cut out in blocks close to the slate formats to manufacture stage during which the splitter takes care to place the longrain, which corresponds to the direction according to which the rock was folded, in the direction length of future slate. Then, the stage comes from the splitting which consists in dividing the block in its thickness, by disuniting the layers of the rock. The last stage, the size, consists in giving to slate its final form.
Use
The slate constitutes material employed for the cover of the buildings (one speaks then about slates ). The traditional areas of production are also the areas where this type of cover is privileged: it acts for example, in France of the Maine-et-Loire and the the Ardennes like in altitude in the Pyrenees.
In general, the slate today is used, because of appearance of synthetic construction materials cheaper, of which some imitating slate (and containing asbestos sometimes).
The slate was also largely used in the form of thin section as an erasable support of writing.
Lifespan
The lifespan of a slate is 70 years to 300 years. The quality of the layer, the type of extraction (machine or hand) and of course the thickness, the type of installation (on hook or studded), the gauge, affect this duration. There is practically no maintenance (démoussage) on slates. For most reliable, it will be necessary to change the support before the slate (change of batten or even of frame). Therefore there is a market of occasion for slates, and that the Historic buildings (their specialized architects and craftsmen) recommend in restoration of slates at long life of life. The slates of bad quality are prone to rust. This defect comes from the presence of iron ore (the most known form is that of the pyrite, but one also meets garnets, magnetite) contents in certain veins of the layer or dispersed. It is thus after the extraction that the defective batches can be put on side systematically by a test at the acid. The treatment of slates on the roof is possible with the passage of chemicals (reaction acid-bases)
The slate differently
The slate is not satisfied any more to cover the roofs, it is useful outside in Dallage, but also inside like scheme of work in Cuisine or bathroom. The slate is carved or engraved. Commemorative plaques, or funerary, plates of streets or decorative are carried out by craftsmen.
Economic importance
According to the investigations of the UNICEM, in 2005, the total sales turnover of the French producers is of: 41147000 euros of which: 20383000 euros with export, in 39 companies or sections of companies.
Museums
The following communes shelter each one a museum dedicated to slate and its local exploitation:
- museum of slate with Trélazé;
- the Blue Mine with Drowning-the-Gravoyère;
- museum of slate with Renazé;
- museum of slate with Fumay;
- house of slate with Rimogne;
- Souterroscope with Caumont-l' Ventilated;
- museum of slate with Haut-Martelange with the Luxembourg;
- center of the interpretation of slate with Mount-Saint-Hilaire with the Quebec
Others
- “More than the hard marble I like
fine slate”: extracted the poem published in 1558 Heureux which like Ulysses , of Joachim of Bellay
See too
Articles of Wikipédia
External bonds
slate|slate
Sources
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