Slate

Slate is a foliated (formed by layers) metamorphic rock created from shale, a sedimentary rock composed of silt and clay size particles we commonly call mud.  It is usually found in a grey colour, although it can present tones of brown, green, purple, or cyan, and it’s popular for many uses including roofing, flooring and landscaping. This stone is mainly composed by clay minerals or micas, depending on the degree of metamorphism it underwent, and it can also contain quartz, feldspar, pyrite, hematite, calcite or other.

Physical properties of this stone, used as building material, are mainly a low moisture absorption and a good frost resistance, which allows uses both indoor and outdoor. Commonly, Slate is being used for internal flooring, external paving, dimension stone and decorative aggregate. In the past, it was also widely used for chalkboards and, thanks to its electrical insulation properties, in electric panels and switch boxes.

In the Mohs hardness scale, Slate scores between 2.5 and 4, depending upon mineral composition of individual types. Although, because of its low compression resistance, this stone is not recommended to be used as kitchen worktop.