Arranged in strings, the plastic clay deposits from Andenne are fillings of cryptokarsts of white and colored clays associated with three layers of Dinantian Frasnian limestone oriented EW. Sands, brown coal and Tertiary (Neogene) clays have accumulated according to thekarstic dissolution forming a pocket of up to 100m deep. The sulphuric acid stemming from the oxidation of sulphides of brown coals is the main responsible for the formation of kaolinitic clays at the expense of clay minerals and the feldspathic sands. The circulation of water induced the leaching of the iron and their accumulation in certain horizons. White clays rich in alumina and of low iron and alkali content were the most looked for their refractory properties. Exploitedat first on surface then in subterranean galleries, the extraction reached its maximal development around the 19 and 20th centuries to stop definitively in 1970. The clay and the white sand were used in the industries of fire: glassware, crystal, metallurgy... and fed the pottery, brick, tile, earthenware factory, porcelain factories, pipe factory and the industrial refractories. The white clay first and then the final products have been exported since the Middle Ages in Holland, Germany and France, contributing to the international reputation of the clays from Andenne. Depressions generated by the subsidence as a consequence of the underground extractions form a string of pools and ponds, sources of biodiversity. Finally, the Ceramics Museum preserves the traces of this remarkable geological, mining, industrial and artistic with its outstanding collections of pottery, porcelain and pipes. Living museum holder of memory, it provides educational and cultural functions from its exhibitions.
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The coticule is an Ordovician aged metamorphic rock only present in the southern part of the Stavelot Massif on the towns of Vielsam and Lierneux. It comes in centimeter thick layers consisting in micrometric crystals of spessartite, microphyllites of micas, infra micrometer quartz. Its exceptional sharpening properties of the metal (razor sharp thin, sharp broad, sharp curve) gave its reputation of a natural abrasive stone and a global distribution (barber, circumciser, surgeon, butcher, carpenter, cabinetmaker, arborist, gardener, winemaker, tanner, coachbuilder ...). Exploited and shaped since the 16th century, the coticule was exported as a whetstone (aka razor stone), the "bouts belges" and to special forms. It was operated by craftsmen, primarily from the surface in open pits, in trenches and then by underground galleries, following the evolution of mining techniques of lighting and drainage. The material was sawn, made in standard sizes and polished by the quarry workers and then in small workshops. The high number of models, the various manufacturing steps entirely manual, the low yield (2-5%), competition from synthetic stones, and the disappearance of part of the customer after the Second World War sounded the death knell of this unique activity. Located in Lierneux, a quarry still operates today the coticule and most of its production is exported to the United States of America. The old mining galleries are today the winter refuge of bats populations. They are considered as cavities of scientific interest. Finally, the Museum of the coticule in Salmchâteau (Vielsalm) presents this manufacturing industry with a global destiny.
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