slate

Slate tiles are a traditional roof covering in many parts of the UK. They are nailed to long batons of wood fixed at intervals across the roof area, which is normally lined for protection against the weather.

Fine-grained, usually grey metamorphic rock that splits readily into thin slabs along its cleavage planes. It is the metamorphic equivalent of shale.

Slate is highly resistant to atmospheric conditions and can be used for writing on with chalk (actually gypsum). Quarrying slate takes such skill and time that it is now seldom used for roof and sill material except in restoring historic buildings.