Slate is a fine-grained, foliated, homogeneous, metamorphic rock. Slate can be made into roofing slates, also called roofing shingles. 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. Sealants are often used on tiles to improve durability and appearance, increase stain resistance, reduce efflorescence, and increase or reduce surface smoothness.