Slate 44214 221416680 2008-06-24T12:09:33Z Socrates2008 5518591 fix link {{other uses}}{{Unreferenced|date=May 2008}} [[Image:SlateUSGOV.jpg|thumb|Slate]] [[Image:Slate Macro 1.JPG|thumb|right|Slate Macro (~ 6 cm long and ~ 4 cm high)]] '''Slate''' is a fine-grained, foliated, [[wiktionary:homogeneous|homogeneous]], [[metamorphic rock]] derived from an original [[shale]]-type [[sedimentary rock]] composed of [[clay]] or [[volcano|volcanic]] [[ash (volcanic)|ash]] through low grade regional [[metamorphism]]. The result is a [[Foliation (geology)|foliated]] rock in which the foliation may not correspond to the original sedimentary layering. Slate is frequently grey in colour especially when seen en masse covering roofs. However, slate occurs in a variety of colours even from a single locality. For example slate from North Wales can be found in many shades of grey from pale to dark and may also be purple, green or [[cyan]]. == Chemical composition == Slate is mainly composed of [[quartz]] and [[muscovite]] or [[illite]], often along with [[biotite]], [[chlorite group|chlorite]], [[hematite]], and [[pyrite]] along with, less frequently, [[apatite]], [[graphite]], [[kaolin]], [[magnetite]], [[tourmaline]], or [[zircon]] as well as [[feldspar]]. Occasionally, as in the purple slates of [[Slate industry in Wales|North Wales]], ferrous reduction spheres form around iron nuclei, leaving a light green spotted texture. These spheres are sometimes deformed by a subsequent applied stress field to ovoids, which appear as ellipses when viewed on a [[cleavage plane]] of the specimen. == Uses of slate == [[Image:St Fagans Tannery 7.jpg|thumb|right|Slate roof]] Slate can be made into [[roof]]ing slates, also called ''roofing [[Roof shingle|shingle]]s'', installed by a [[slater]] in the USA. Slate 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 (tool)|whetstone]] to hone knives. Due to 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 [[Chalkboard|blackboards]] and individual [[Slate (writing)|writing slates]] for which chalk pencils were used. Because it is a good [[electrical insulator]] and [[fireproof]], it was used to construct early 20th century [[electric switchboard]]s and [[relay]] controls for large [[electric motor]]s. British sculptor [[Stephen Kettle]] is notable for his use of slate to create statues housed in the [[Science Museum]] in London. 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 [[efflorescence]], and increase or reduce surface smoothness. Tiles are often sold gauged, meaning that the back surface is ground for ease of installation. Slate tiles were used in 19th century UK building construction (apart from roofs). They can be set into the walls to provide a rudimentary [[damp-proof membrane]]. Small offcuts are used as [[shim (engineering)|shims]] to level floor joists. Slate is often used as a decor in freshwater aquariums. Slate will not alter the chemistry of water (except in the slate containing feldspar which may leach silicates into the water resulting in excess diatom growth in marine aquaria). When broken, slate produces a natural appearance while remaining relatively flat and can be easily stacked. Silicone glue adheres to slate, creating a non-toxic bond to secure it. It is also used in stairs and pathways for the same reasons. Traditional Japanese [[Go (board game)|Go]] equipment uses slate for the black pieces. == Slate extraction == [[Image:bergwerk-fell-hoffnung.jpg|thumb|[[Fell Exhibition Slate Mine|Exhibition Slate mine Fell]]]] [[Image:bergwerk-fell-stollen2.jpg|thumb|Historical Pit ''Vogelsberg 1'' at Fell]] Slate-producing regions in Europe include [[Wales]] (see [[slate industry in Wales]]), [[Cornwall]] (famously the town of [[Delabole]]), and Cumbria (see [[Burlington Slate Quarries]], [[Honister Slate Mine]] and [[Skiddaw Slate]]) in the [[United Kingdom]]; parts of France (Angers, Anjou and in the Maritime Alps); Belgium (formerly); [[Liguria]] in northern [[Italy]] especially between the town of Lavagna (which means chalkboard in Italian) and Fontanabuona valley; [[Portugal]] especially around [[Valongo]] in the north of the country; [[Germany]]'s ([[Moselle River]]-region, [[Hunsrück]], [[Eifel]], [[Westerwald]], [[Thuringia]] and north-[[Bavaria]]); [[Alta, Norway]] (actually schist not a true slate) and [[Galicia (Spain)|Galicia]]. In the Americas, slate is found in Brazil (the second biggest producer of slate) around [[Papagaio]] in [[Minas Gerais]] (responsible for 95% of the extraction of slate in Brazil), the east coast of [[Newfoundland (island)|Newfoundland]], the Slate Belt of Eastern [[Pennsylvania]], and the [[Slate Valley]] of [[Vermont]] and [[New York]]. The area around [[Granville, NY]], is one place where [[colored slate]] (non-blue) is mined. Others include Wales (purple and formerly green) and Cumbria (green) in the UK; Brazil (green); China (many colors); and Newfoundland. {{Fact|date=November 2007}} There was also a major slating operation in [[Monson, Maine]] during the late 19th and early 20th centuries. The slate found in Monson is usually a dark purple to blackish color, and many local structures are still roofed with slate tiles. Of many operations there is only one business currently operating. The output was so great it formed a [[Monson Railroad|train]] route throughout the woods of Monson and as many as 18 quarries were made. [[St. Patrick's Cathedral, New York|St. Patricks's Cathedral]] in New York's roof was made from roofing slate from Monson, as well as the Headstone of John F. Kennedy. Slate is also found in the [[Arctic]] and was used by the [[Inuit]] to make the blades for [[ulu]]s. China has vast slate deposits; in recent years its export of finished and unfinished slate has increased. ==See also== *[[List of rock types]] *[[Tile]] *[[National Slate Museum]] *[[Fell Exhibition Slate Mine]] *[[Slate industry in Wales]] ==External links== * [http://www.aditnow.co.uk/ AditNow] - Photographic database of mines *[http://www.slateroof.co.uk/ddpint.html History of the Welsh slate industry] *[http://cornovia.org.uk/htexts/turner01.html John T F Turner - A Familiar Description of the Old Delabole Slate Quarries, 1864] *[http://www.slate.org.uk/ History of the Scottish Slate Islands] *Granville Slate Museum [http://www.slatevalleymuseum.org/] [[Category:Metamorphic rocks]] [[Category:Materials]] [[Category:Stone]] [[Category:Dielectrics]] [[ca:Pissarra]] [[cy:Llechfaen]] [[da:Skifer]] [[de:Schiefer]] [[et:Kilt]] [[es:Pizarra]] [[eo:Ardezo]] [[fr:Ardoise]] [[it:Ardesia]] [[he:צפחה]] [[nl:Leisteen]] [[ja:粘板岩]] [[no:Skifer]] [[pl:Łupek]] [[pt:Ardósia]] [[fi:Saviliuske]] [[sv:Skiffer]] [[zh:板岩]]