Slate

Slate is the fine grained foliated homogeneous metamorphic rock derived from an orginal shale- type sedimentry rock .Which is composed of clay or volcanic ash through low grade regional metamorphism.Its is the finest grained foliated(i.e) that is foliation maens in geology refers to repetitive layering in metamorphic rocks.Each layer may be as thin as a sheet of papers or over a meter in thickness.

The word comes from latin folium , meaning ''leaf" and refers to the sheet like planar structure.It is caused by shearing forcespushing different sections of the rock in different directions .The layer form parellel to the direction of shear or perpendicular to the direction of higher pressure .A very strong foliation is callled slaty clevage.The slaty cleavage typical of slate is due to the preffered orientation of microscapic .Phyllo sillicate crystals .It is caused by strong compression causing fine grained clay flakes to regrow in planes perpendicular to the compression