Slate is a fine-grained, foliated, , 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 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, 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 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

Slate can be made into roofing slates, also called "roofing shingles", installed by a slater. 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 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 blackboards and individual 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 switchboards and relay controls for large electric motors. 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 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 equipment uses slate for the black pieces.

Slate extraction

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. 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, 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 train route throughout the woods of Monson and as many as 18 quarries were made. The roof of St. Patrick's Cathedral was made of roofing slate from Monson, as was the Headstone of John F. Kennedy.

Slate is also found in the Arctic and was used by the Inuit to make the blades for ulus. China has vast slate deposits; in recent years its export of finished and unfinished slate has increased.

ee also

*List of rock types
*National Slate Museum
*Fell Exhibition Slate Mine
*Slate industry in Wales

External links

* [ AditNow] - Photographic database of mines
* [ History of the Welsh slate industry]
* [ John T F Turner - A Familiar Description of the Old Delabole Slate Quarries, 1864]
* [ History of the Scottish Slate Islands]
*Granville Slate Museum []

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Look at other dictionaries:

  • Slate — (sl[=a]t), n. [OE. slat, sclat, OF. esclat a shiver, splinter, F. [ e]clat, fr. OF. esclater to shiver, to chip, F. [ e]clater, fr. OHG. sleizen to tear, slit, split, fr. sl[=i]zan to slit, G. schleissen. See {Slit}, v. t., and cf. {Eclat}.] 1.… …   The Collaborative International Dictionary of English

  • Slate ax — Slate Slate (sl[=a]t), n. [OE. slat, sclat, OF. esclat a shiver, splinter, F. [ e]clat, fr. OF. esclater to shiver, to chip, F. [ e]clater, fr. OHG. sleizen to tear, slit, split, fr. sl[=i]zan to slit, G. schleissen. See {Slit}, v. t., and cf.… …   The Collaborative International Dictionary of English

  • — Slate (magazine) Slate (ardoise en français) est un magazine en ligne américain. Depuis février 2009, il existe également une version française. Sommaire 1 2 3 Source et références 4 …   Wikipédia en Français

  • Slate — Slate, v. t. [imp. & p. p. {Slated}; p. pr. & vb. n. {Slating}.] 1. To cover with slate, or with a substance resembling slate; as, to slate a roof; to slate a globe. [1913 Webster] 2. To register (as on a slate and subject to revision), for an… …   The Collaborative International Dictionary of English

  • slate — slate1 [slāt] n. [ME sclate < OFr esclate, fem. of esclat: see SLAT1] 1. a hard, fine grained, metamorphic rock, typically formed from shale, that cleaves naturally into thin, smooth surfaced layers 2. a thin piece of slate or slatelike… …   English World dictionary

  • Slate — steht für: Slate (Programmiersprache), eine objektorientierte Programmiersprache Slate (Tablet PC), eine Bauform eines Tablet PCs Slate (Magazin), ein englischsprachiges Online Magazin einen Ortsteil der Kreisstadt Parchim in Mecklenburg… …   Deutsch Wikipedia

  • Slate 20 — is brand of alcopop (as it is commonly referred to) although is part of the RTD ready to drink market. It is available in 275ml and 700ml bottles. Slate 20 is owned and distributed by Diageo. The drink is packaged in brown glass bottles with a… …   Wikipedia

  • slate — slate; slate·man; un·slate; …   English syllables

  • Slate — Slate, v. t. [Cf. AS. sl[=ae]ting a privilege of hunting.] To set a dog upon; to bait; to slat. See 2d {Slat}, 3. [Prov. Eng. & Scot.] [Written also {slete}.] Ray. [1913 Webster] …   The Collaborative International Dictionary of English

  • slate — [sle:t, engl. sleit] <zu engl. slate »Schiefer«> schiefergrau gefärbt (von Rauchwaren) …   Das große Fremdwörterbuch

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