L ' slate (also known as Blackboard stone or, in some dialects Alpine Piöda ) is a variety of allotigena metamorphic rock of sedimentary origin, widespread in northern Italy and for many centuries extracted from quarries in the valley Fontanabuona in Liguria of Cuneo in Piedmont and Valcamonica , Lombardy.
result of progressive sedimentation of fine silt (marl ) due to fragmentation of ancient mountains, slate is a rock classified as semi-soft or hard. This is a special variety of limestone and clay shale can be split easily into thin slabs, flat, lightweight, waterproof and weatherproof. It is a stone very carcarifica and compact, color leaden - blackish and workable. Slate tends to clear from their extraction up to take a light gray pigmentation, the darker shade being due to excess carbon that evaporate when in contact with oxygen , moisture and ultraviolet radiation . By virtue of its schistosity (ie ability to divide and plates) and properties can be used in various segments of both artisanal and industrial ' architecture and of' building (for roofing, flooring, stair steps) and in art in and design of objects of everyday use.
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