Ardennes Slate

Ardennes slate is natural roofing slate from the Ardennes, the upland region shared by southern Belgium, the French département of Ardennes and northern Luxembourg. Quarried from at least the Middle Ages, it roofed houses, churches and abbeys across the Low Countries and northern France. Production in Belgium and Luxembourg ended in the 1970s and 1980s, but the slate-roofed villages and old workings remain an important part of the region's heritage.

Geology

The Ardennes slate belt consists of schists and phyllites. Around Vielsalm in Belgium the beds dip steeply, at about 55-60 degrees, and include phyllites containing the mineral ottrelite. The same area yields coticule, a fine whetstone used for sharpening razors.

Early use

Schist plaques engraved during the Magdalenian period (roughly 17,000-10,000 years ago) have been found at sites including Monthermé in France and the Trou de Chaleux cave in Belgium. In Roman and Gallo-Roman times slate was used mainly for floors and for tombs, such as the slate-walled graves of a cemetery at Bihain. Roofing slate appears in documents from the 12th century: in 1156 the abbey of Saint-Trond is said to have been roofed with slate from Fumay in the French Meuse valley. The monks of Orval held a quarry at Herbeumont, confirmed in 1269 and again in 1306, and slate working at Vielsalm is recorded from 1481.

Industrial peak

In the Belgian province of Luxembourg, 480 workers produced about 17 million slates in 1840. Output reached about 41 million slates in 1873 and 1876, when 1,108 people worked in the industry, and in 1877 there were 51 open-air and 116 underground workings. The main Belgian basins were around Herbeumont, Bertrix, Cugnon and Martelange, and around Vielsalm. Across the border, the Haut-Martelange mines in the Grand Duchy of Luxembourg produced about 6 million slates a year by the end of the 19th century.

Decline

Competition from tiles, other roofing materials and cheaper imported slate reduced demand through the 20th century. Major Vielsalm quarries closed in 1884-1886, others in 1930, 1944 and 1968, and Vielsalm's production ended in 1972. The last Luxembourg mine, at Haut-Martelange, closed in 1986, and Martelange, the last Belgian slate site, closed at the end of the 1980s. In the French Ardennes, former slate centres such as Rimogne are now part of a tourist "slate route".

Uses

Roofing was the main use, valued for fire resistance and durability. Slate was also made into floor slabs, school writing slates, billiard tables, sinks, laboratory crucibles and sawn slabs.

Sources and gaps

Technical test data for Ardennes slate under EN 12326: published information is limited.