[LUM#2] Stone hunters
In the heart of the Lozère region, lauziers perpetuate a know-how that goes back thousands of years. With the help of geologists and their high-tech tools.

Kneeling in the middle of the quarry, the man hammers away at a rock weighing several hundred kilos. From this brown-veined giant, he extracts sheets a few centimetres thick, the lauzes that will be used to make roofs. It's an age-old skill that can't be faulted. Lauzes can break like glass...
" You have to know the stone, feel it, so as not to break it," explains Roland Jacques. His tools? A simple sledgehammer and a trained ear. " We make the stone sound. You listen to it sing, to know if it has a flaw. His job? Carrier. An endangered profession: in his village of Lachamp, Lozère, Roland Jacques operates one of the region's last slate quarries.
Better detection of deposits
" When you're digging, you never really know what you're going to find," explains Roland Jacques. The jackpot: large sections of intact stone that can be cut into beautiful lauzes. Unfortunately, the quarryman sometimes has the unpleasant surprise of uncovering broken, unusable rock. " The sedimentary formations identified at Lachamp are affected by late fracturing, which makes the quality of the extracted stone uncertain ", explains Cédric Champollion, geologist at the Géosciences Montpellier laboratory.
How can we help quarrymen better detect deposits? Romain Duhamel, a geosciences master's student, took up the challenge. " We set out to identify the least fractured zones using geophysical prospecting ". Quarrymen make stone sing? He's going to make it talk. His tools: georadar and electric probing.
Radar to the hammer's rescue
" Georadar sends waves into the ground which propagate differently depending on the nature of the rock. By analyzing their propagation, we can estimate the state of the subsoil," explains Romain Duhamel. The same principle applies to electrical probing: using electrodes, the geologist injects a current which, by measuring the resistivity of the subsoil, detects the possible presence of fractures.
"This is the first time such a method has been used," explains Romain Duhamel. And with success: "it gave totally consistent results when we compared the profiles obtained with the state of the rocks visible on the surface ", enthuses the geology student. " It helps me to know exactly where to attack the work on my quarry ," says Roland Jacques. " It's quite simply extraordinary for us lauziers - we'd never have had this information otherwise. And if tomorrow a young person wants to open a new quarry, he'll need this." To perpetuate a priceless tradition and know-how, and to ensure that for a long time to come the people of Lachamp will be known as coperoches, or "stone cutters".

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