What is slate?

Millions of years ago, fine grains of clay particles settled on the bottom of lakes and seas, forming soft mud. This became hardened mud-rock called shale. Around this time, the earth’s crust moved and shifted. The shale layers, covered by beds of other rocks, were flattened and squeezed hard. Thus the shale became slate. Slate is used as roofing material for buildings and making blackboards, table tops and draining boards.