Slate is a very fine-grained metamorphic rock that easily splits into characteristic, thin slices, i.e. it is very cleavable. Slate is characteristically grey or grey-blue (but can also be black, green, purple, red, or brown).  Because it is composed mainly of fine-grained mica flakes and quartz, it is intermediate in hardness, but can still be scratched by metal.  It has a dull luster and strong cleavage.  Its nonabsorbent properties and durability make it a popular material for roof tiles and paving slabs, and in some cases it is used for wall construction.

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Slate stone used for wall construction in coastal areas of Chile (S. Brzev)

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Slate stone used for wall construction, Pakistan (S.H.Lodi)