Stone : amphibolite
Type : metamorphic rock derived from a magmatic rock
Age : 588 million years
Quarry : Kerpointel, Tressignaux (Côtes d’Armor)

Homemade Breton Pebbles

In Tressignaux, quarry workers have ventured into pebble-making. The recipe is kept secret. However, the machine used reportedly resembles a giant washing machine capable of handling up to 6 tons of rock blocks. After a polishing cycle lasting a day and a half, the blocks are transformed into beautifully rounded pebbles.

Ancient Volcanic Rocks

The amphibolite of Tressignaux—where the best outcrops of this rock are found—is part of the Lanvollon Formation, specifically the Roselier Member. Amphibolites also crop out along the coast, particularly at Pointe du Roselier (northwest of the Bay of Saint-Brieuc). Most of the volcanic rocks in this formation, dated to 588 million years ago (Brioverian), are ancient basalts that formed in a tectonic context of intracontinental rifting.

From Stones to Generations

The quarry has been in operation for three generations (since 1947). Each day, nearly 2,000 tonnes of rock are extracted—amounting to 300,000 to 500,000 tonnes per year. Most of the aggregate production is used for public works. In recent years, in addition to crafting pebbles, the quarry has also begun selling materials sourced from various locations.

The Gigantism of Quarries

This old, rusted loader bucket is a reminder that extractive industries are anything but small! The machinery is large and powerful. In aggregate-focused quarries like Tressignaux, an excavator at the quarry face loads materials into dump trucks, which transport them to the crusher. The materials are then screened and stockpiled in mounds of variously sized aggregates.