Welsh Slate

Slate is a grey/blue/green-ish metamorphic rock that is formed from layers of shale, a sedimentary rock that is deposited on the bed of streams and rivers. Over vast periods of time, as the layers of shale dust build up, so does the heat and pressure exerted on these layers, which causes the metamorphic transformation from shale to slate. Slate is found in mountainous regions, explaining its presence in northwest Wales, where mining reached its peak in the 1800s and is still excavated to this day, though on a much smaller scale. Slate contains what is known as a cleavage plane – a brittle layer that separates thin sheets of slate. Tapping along this plane with a hammer and chisel enables the layers to separate, forming a smooth tile typically used for roofing and flooring.