Slate

rocks · metamorphic · building material

Born from shale. Slate starts as shale, a soft sedimentary rock made of clay or volcanic ash. Deep underground, heat and pressure transform it into something much harder and tougher.

Splits into sheets. Slate naturally breaks into thin, flat sheets that are almost like stacked paper. This happens because of how the minerals line up when the rock is squeezed during metamorphism.

Built human history. For centuries, people have used slate to make roofs, floors, chalkboards, and tombstones because it's durable and splits so cleanly into usable pieces.

Super fine-grained. Slate has the smallest grain size of any foliated metamorphic rock, which makes it smooth to the touch and perfect for writing on with chalk.

Compression creates pattern. The layers and patterns in slate point in the direction that the rock was squeezed, not the way the original shale layers sat down.