They come from the modification, in solid state, of igneous or sedimentary rocks due to the conditions of temperature and pressure or tectonic efforts to which they were subjected. Metamorphic processes cause changes in mineralogy and texture in rocks and, in some cases, also in chemical composition.

Slate belongs to the group of metamorphic rocks. It is of fine grain, with structure in slabs. The original rock was a shale, which was affected by a low-grade metamorphism (process by which one rock is transformed into another, reflecting changes in composition and texture).

Age: Cambrian-Ordovician. Places: Capdella, Filià.

Uses: Roof coverings in areas of snow and other types of constructions. Old writing element. Kitchen.