Slate is a fine-grained, homogeneous, metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary layering.

Slate can be made into roofing slates, also called roofing shingles, because it has two lines of breakability: cleavage and grain. This makes it possible to split slate into thin sheets. Fine slate can also be used as a whetstone to hone knives. Because of its thermal stability and chemical inertness, slate has been used for laboratory bench tops and for billiard table tops. In 18th and 19th century schools, slate was extensively used for blackboards and individual writing slates for which slate pencils were used.

Slate tiles are often used for interior and exterior flooring or wall cladding. Tiles are installed and set on mortar and grouted along the edges. Chemical sealants are often used on tiles to improve durability and appearance, increase stain resistance, reduce efflorence, and increase or reduce surface smoothness. Tiles are often sold gauged, meaning that the back surface is ground for ease of installation.

Slate is often used as a decor in freshwater aquariums. Slate will not alter the chemistry of water. When broken, slate produces a natural appearance while remaining relatively flat and can be easily stacked. Silicon glue adheres to slate, creating a non-toxic bond to secure it.