SLATE PAVING STONE
Slate is a popular stones used for garden patios and paths.
Slate is metamorphosed shale. Shale is made up of silt and clay that is similar in composition to sandstone except that the particle size is much smaller. The shale is subject to heat and pressure and the fine particles are melted together to form slate.
Slate naturally has a riven surface, where the stone splits due to a natural cleavage. This textured surface is great for grip. For ease of laying, most slate paving slabs are calibrated to the same thickness, which means they are completely flat on the underside.