View source for Slate

{{Short description|Metamorphic rock}}
{{Other uses}}
{{Use dmy dates|date=October 2019}}
{{Infobox rock
|name=Slate
|type=Metamorphic
|type_link=Metamorphic Rock
|image=Slate (Knife Lake Formation, metamorphism at 2.7 Ga, Neoarchean; Rt. 135 roadcut, Gilbert, Minnesota, USA) 3 (23140002749).jpg
|caption=Slate at Knife Lake Formation
|composition=[[quartz]], [[muscovite]]/[[illite]]
|composition_secondary=[[biotite]], [[Chlorite group|chlorite]], [[hematite]], [[pyrite]]
Specific gravity: 2.7 – 2.8,2.9
}}
'''Slate''' is a fine-grained, [[foliation (geology)|foliated]], 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]]. It is the finest-grained foliated metamorphic rock.<ref name=EG>{{cite book|title=Essentials of Geology|edition=3rd|first=Stephen|last=Marshak}}{{page needed|date=July 2021}}</ref> Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression.<ref name=EG/>
The foliation in slate, called "[[slaty cleavage]]",<ref name=EG/> is caused by strong compression in which fine-grained clay forms flakes to regrow in planes perpendicular to the compression.<ref name=EG/> When expertly "cut" by striking parallel to the foliation with a specialized tool in the quarry, many slates display a property called [[fissility (geology)|fissility]], forming smooth, flat sheets of stone which have long been used for [[roof]]ing, floor tiles, and other purposes.<ref name=EG/> Slate is frequently grey in color, especially when seen'' en masse'' covering roofs. However, slate occurs in a variety of colors 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. Slate is not to be confused with shale, from which it may be formed, or [[schist]].
The word "slate" is also used for certain types of object made from slate rock. It may mean a single roofing tile made of slate, or a [[Slate (writing)|writing slate]], which was traditionally a small, smooth piece of the rock, often framed in wood, used with chalk as a notepad or notice board, and especially for recording charges in pubs and inns. The phrases "clean slate" and "[[tabula rasa|blank slate]]" come from this usage.
==Description==
[[File:Slate with pyrite.JPG|thumb|Slate with [[pyrite]]]]
Slate is a fine-grained, metamorphic rock that shows no obvious compositional layering but can easily be split into thin slabs and plates.<ref name="BGS">{{cite journal |last1=Robertson |first1=S. |title=BGS Rock Classification Scheme, Volume 2: Classification of metamorphic rocks |journal=British Geological Survey Research Report |date=1999 |volume=RR 99-02 |url=http://nora.nerc.ac.uk/id/eprint/3226/1/RR99002.pdf |archive-url=https://web.archive.org/web/20180403144017/http://nora.nerc.ac.uk/id/eprint/3226/1/RR99002.pdf |archive-date=2018-04-03 |url-status=live |access-date=27 February 2021}}</ref><ref>{{cite book |last1=Allaby |first1=Michael |title=A Dictionary of Geology and Earth Sciences |date=2013 |publisher=Oxford University Press |location=Oxford |isbn=9780199653065 |edition=4th |chapter=Slate}}</ref> It is usually formed by low-grade [[regional metamorphism]] of [[mudrock]].<ref name=Jackson>{{cite book |editor1-last=Jackson |editor1-first=Julia A. |title=Glossary of Geology |date=1997 |publisher=American Geological Institute |location=Alexandria, VA |isbn=0922152349 |edition=4th |chapter=Slate}}</ref><ref name=BlattTracy>{{cite book |last1=Blatt |first1=Harvey |last2=Tracy |first2=Robert J. |title=Petrology: Igneous, Sedimentary, and Metamorphic |date=1996 |publisher=W.H. Freeman |location=New York, NY |isbn=0716724383 |edition=2nd |page=365}}</ref> This mild degree of metamorphism produces a rock in which the individual mineral crystals remain microscopic in size,<ref name=BlattTracy/> producing a characteristic [[slaty cleavage]] in which fresh cleavage surfaces appear dull. This is in contrast to the silky cleaved surfaces of [[phyllite]], which is the next-higher grade of metamorphic rock derived from mudstone.<ref>{{cite book |last1=Yardley |first1=B. W. D. |title=An Introduction to Metamorphic Petrology |date=1989 |publisher=Longman Scientific & Technical |location=Harlow, Essex |isbn=0582300967 |page=22}}</ref> The direction of cleavage is independent of any [[sedimentary structures]] in the original mudrock, reflecting instead the direction of regional compression.<ref>{{cite book |last1=Potter |first1=Paul Edwin |last2=Maynard |first2=J. Barry |last3=Pryor |first3=Wayne A. |title=Sedimentology of Shale |date=1980 |publisher=Springer-Verlag |location=New York |isbn=0387904301 |page=17}}</ref>
Slaty cleavage is continuous, meaning that the individual cleavage planes are too closely spaced to be discernible in hand samples. The [[Texture (geology)|texture]] of the slate is totally dominated by these pervasive cleavage planes. Under a microscope, the slate is found to consist of very thin lenses of [[quartz]] and [[feldspar]] (QF-domains) separated by layers of [[mica]] (M-domains).<ref name=Fossen>{{cite book |last1=Fossen |first1=Haakon |title=Structural Geology |date=2016 |publisher=Cambridge University Press |location=Cambridge |isbn=9781107057647 |edition=2nd |pages=287–289}}</ref> These are typically less than 100 μm (micron) thick.<ref name=Jackson/> Because slate was formed in low heat and pressure, compared to most other metamorphic rocks, some [[fossils]] can be found in slate; sometimes even microscopic remains of delicate organisms can be found in slate.<ref>BBC Video: ''[[David Attenborough]]: Lost Worlds, Vanished Lives''</ref><ref>{{cite journal |last1=Glass |first1=Alexander |last2=Blake |first2=Daniel B. |date=April 2004 |title=Preservation of tube feet in an ophiuroid (Echinodermata) from the Lower Devonian Hunsrück Slate of Germany and a redescription of ''Bundenbachia beneckei'' and ''Palaeophiomyxa grandis'' |journal=Paläontologische Zeitschrift |volume=78 |issue=1 |pages=73–95 |bibcode=2004PalZ...78...73G |doi=10.1007/BF03009131 |s2cid=140689763}}</ref>
The process of conversion of mudrock to slate involves a loss of up to 50% of the volume of the mudrock as it is compacted. Grains of platy minerals, such as [[clay minerals]], are rotated to form parallel layers perpendicular to the direction of compaction, which begin to impart cleavage to the rock. Slaty cleavage is fully developed as the clay minerals begin to be converted to [[chlorite group|chlorite]] and mica. Organic carbon in the rock is converted to [[graphite]].{{sfn|Yardley|1989|pp=64, 170}}
Slate is mainly composed of the minerals quartz, [[illite]], and chlorite, which account for up to 95% of its composition. The most important accessory minerals are iron oxides (such as [[hematite]] and [[magnetite]]), iron sulfides (such as [[pyrite]]), and carbonate minerals. Feldspar may be present as [[albite]] or, less commonly, [[orthoclase]].<ref>{{cite journal |last1=Walsh |first1=Joan A. |title=The use of the scanning electron microscope in the determination of the mineral composition of Ballachulish slate |journal=Materials Characterization |date=November 2007 |volume=58 |issue=11–12 |pages=1095–1103 |doi=10.1016/j.matchar.2007.04.013}}</ref> Occasionally, as in the purple slates of [[Slate industry in Wales|North Wales]], ferrous ([[iron(II)]]) reduction spheres form around iron nuclei, leaving a light-green, spotted texture. These spheres are sometimes deformed by a subsequent applied stress field into ovoids, which appear as ellipses when viewed on a cleavage plane of the specimen. However, some evidence shows that reduced spots may also form after deformation and acquire an elliptical shape from preferential infiltration along the cleavage direction, so caution is required in using reduction ellipsoids to estimate deformation.{{sfn|Fossen|2016|p=61}}
== Terminology ==
Before the mid-19th century, the terms "slate", "[[shale]]", and "[[schist]]" were not sharply distinguished.<ref>{{cite book|first=R. W. |last=Raymond |chapter=Slate |chapter-url=https://books.google.com/books?id=FpqFAAAAIAAJ&pg=PA78 |title=A Glossary of Mining and Metallurgical Terms |publisher=American Institute of Mining Engineers |date=1881 |page=78}}</ref> In the context of underground [[coal mining]] in the United States, the term slate was commonly used to refer to shale well into the 20th century.<ref>{{cite book|first=Albert H. |last=Fay |chapter=Slate |chapter-url=https://books.google.com/books?id=y6hCAAAAIAAJ&pg=PA622 |title=A Glossary of the Mining and Mineral Industry |publisher=United States Bureau of Mines |date=1920 |page=622}}</ref> For example, roof slate referred to shale above a [[coal seam]], and draw slate referred to shale that fell from the mine roof as the coal was removed.<ref>{{cite book|editor-first=J. Marvin |editor-last=Weller |url=https://books.google.com/books?id=6UIrAAAAYAAJ&pg=RA1-PA18 |title=Supplement to the Glossary of Geology and Related Sciences |publisher=American Geological Institute |date=1960 |page=18}}</ref>
The [[British Geological Survey]] recommends that the term "slate" be used in scientific writings only when very little else is known about the rock that would allow a more definite classification. For example, if the characteristics of the rock show definitely that it was formed by metamorphosis of shale, it should be described in scientific writings as a metashale. If its origin is uncertain, but the rock is known to be rich in mica, it should be described as a [[pelite]].<ref name="BGS"/>
==Uses==
{{see also|Flagstone}}
===Construction===
[[File:St Fagans Tannery 7.jpg|thumb|A slate roof in [[Cardiff]], Wales]]
[[File:Kirche wurzbach.jpg|thumb|A slate-faced church and homes in [[Wurzbach]], Germany]]
[[File:St.leonhard-ffm002.jpg|thumb|upright|A fine slate tile work, Saint Leonhard's Church in [[Frankfurt am Main]], Germany]]
[[File:SlateTremedda.jpg|thumb|Slates with holes at a farm in [[Tremedda]], [[Cornwall]], England]]
Slate can be made into roofing slate, a type of [[Roof tiles|roof tile]] which are installed by a [[slater]]. Slate has two lines of breakability—cleavage and grain—which make it possible to split the stone into thin sheets. When broken, slate retains a natural appearance while remaining relatively flat and easy to stack. A series of "slate booms" occurred in Europe from the 1870s until the [[World War I|First World War]] following improvements in railway, road and waterway transportation systems.<ref>{{cite book|last1=Schunck |first1=Eberhard |first2=Hans Jochen |last2=Oster |title=Roof Construction Manual Pitched Roofs |location=Basel |publisher=De Gruyter |date=2003 |page=12 |edition=print}}</ref>
Slate is particularly suitable as a roofing material as it has an extremely low water absorption index of less than 0.4%, making the material resistant to frost damage.<ref name=NPS>{{cite web |last1=Chavez |first1=Mark |date=2013 |title=Should I Replace My Slate Roof with a Synthetic? |url=https://www.nps.gov/articles/should-i-replace-my-slate-roof-with-a-synthetic.htm |website=National Park Service |access-date=28 June 2021}}</ref> Natural slate, which requires only minimal processing, has an [[embodied energy]] that compares favorably with other roofing materials.<ref>{{cite journal |last1=Crishna |first1=N. |last2=Banfill |first2=P.F.G. |last3=Goodsir |first3=S. |title=Embodied energy and CO2 in UK dimension stone |journal=Resources, Conservation and Recycling |date=October 2011 |volume=55 |issue=12 |pages=1265–1273 |doi=10.1016/j.resconrec.2011.06.014}}</ref>
Natural slate is used by building professionals as a result of its beauty and durability. Slate is incredibly durable and can last several hundred years,<ref>{{cite journal |last1=Cárdenes |first1=Víctor |last2=Cnudde |first2=Jean Pierre |last3=Wichert |first3=Jörn |last4=Large |first4=David |last5=López-Mungira |first5=Aurora |last6=Cnudde |first6=Veerle |title=Roofing slate standards: A critical review |journal=Construction and Building Materials |date=July 2016 |volume=115 |pages=93–104 |doi=10.1016/j.conbuildmat.2016.04.042}}</ref> often with little or no maintenance.<ref name=NPS/> Natural slate is also fire resistant and energy efficient.<ref>[http://www.insightmag.co.uk/newsarticle.asp?NewsID=286 Natural Slate, the natural option] {{webarchive|url=https://web.archive.org/web/20140310123813/http://www.insightmag.co.uk/newsarticle.asp?NewsID=286 |date=10 March 2014 }}</ref>
Slate roof tiles are usually fixed (fastened) either with nails or with hooks (as is common with Spanish slate).<ref>{{cite web |title=Slate Design and Fixing Guide |url=https://www.ssqgroup.com/wp-content/uploads/2022/12/SSQ-Natural-Slate-Design-Fixing-Guide.pdf |access-date=28 June 2021 |publisher=SSQ Group}}</ref> In the UK, fixing is typically with double nails onto timber battens (England and Wales)<ref>{{cite web |title=Natural roofing slate design and fixing guide |url=https://www.ssqgroup.com/wp-content/uploads/2022/12/SSQ-Natural-Slate-Design-Fixing-Guide.pdf |url-status=live |archive-url=https://web.archive.org/web/20190626011731/http://ssqslate.com/wp-content/uploads/2012/10/SSQ_Slate_Fixing_Guide_Nail_Fixings.pdf |archive-date=2019-06-26 |access-date=28 June 2021 |publisher=SSQ Group |page=8}}</ref> or nailed directly onto timber sarking boards (Scotland and Northern Ireland).{{citation needed|date=June 2021}} Nails were traditionally of copper, although there are modern alloy and stainless steel alternatives.<ref>{{cite web |title=6 Basic Principals of Slate Roofing |date=3 August 2017 |url=https://slateassociation.org/6-basic-principals-slate-roofing/ |publisher=National Slate Association |access-date=28 June 2021}}</ref> Both these methods, if used properly, provide a long-lasting weathertight roof with a lifespan of around 60–125 years.<ref name=NPS/>
Some mainland European slate suppliers suggest that using hook fixing means that:<ref>[http://www.spanishslateuk.com/hook_fixing.asp Galician and Spanish Slate website "Hook Fixing"]. Retrieved on 26 January 2010 [https://web.archive.org/web/20110716113747/http://www.spanishslateuk.com/hook_fixing.asp archived]</ref>
* Areas of weakness on the tile are fewer since no holes have to be drilled
* Roofing features such as valleys and domes are easier to create since narrow tiles can be used<ref name=SSQHook>{{cite web |title=Hook fixing |url=http://ssqslate.com/wp-content/uploads/2013/05/SSQ_Slate_Fixing_Guide_Hook_Fixings.pdf |archive-url=https://web.archive.org/web/20190626010851/http://ssqslate.com/wp-content/uploads/2013/05/SSQ_Slate_Fixing_Guide_Hook_Fixings.pdf |archive-date=2019-06-26 |url-status=live |publisher=SSQ Group |access-date=28 June 2021}}</ref>
* Hook fixing is particularly suitable in regions subject to severe weather conditions, since there is greater resistance to wind uplift, as the lower edge of the slate is secured.<ref name=SSQHook/>
The metal hooks are, however, visible and may be unsuitable for historic properties.
Slate tiles are often used for interior and exterior flooring,<ref name=bobvilafloor>{{cite web |last1=Taylor |first1=Glenda |last2=Vila |first2=Bob |title=All You Need to Know About Slate Floors |url=https://www.bobvila.com/articles/slate-floors/ |website=bob vila |date=11 August 2016 |publisher=Action Media, Inc. |access-date=28 June 2021}}</ref> stairs,<ref>{{cite web |last1=Robinson |first1=Kristy |title=Installing Slate Tiles on Front Stairs |url=https://homeguides.sfgate.com/installing-slate-tiles-front-stairs-33718.html |website=SFGate |date=2 July 2012 |publisher=Hearst |access-date=28 June 2021}}</ref> walkways<ref>{{cite web |title=How to Lay a Walkway with Slate Pavers |url=https://www.doityourself.com/stry/how-to-lay-a-walkway-with-slate-pavers |website=doityourself |access-date=28 June 2021}}</ref> and wall cladding.<ref>{{cite web |last1=Asaff |first1=Sarabeth |title=How to Install Exterior Slate Tile |url=https://homeguides.sfgate.com/glass-tile-thickness-make-difference-92797.html |website=SFGate |date=December 2013 |publisher=Hearst |access-date=28 June 2021}}</ref> Tiles are installed and set on mortar and grouted along the edges. Chemical sealants are often used on tiles to improve durability and appearance,<ref name=thespruce/> increase stain resistance,<ref name=bobvilafloor/> reduce [[efflorescence]], and increase or reduce surface smoothness. Tiles are often sold gauged, meaning that the back surface is ground for ease of installation.<ref name=thespruce>{{cite web |last1=Lewitin |first1=Joseph |title=Everything You Need to Know About Slate Flooring Tiles |url=https://www.thespruce.com/all-about-slate-flooring-tiles-1314931 |website=The Spruce |publisher=Dotdash |access-date=28 June 2021}}</ref> Slate flooring can be slippery when used in external locations subject to rain.
Slate tiles were used in 19th century UK building construction (apart from roofs) and in slate quarrying areas such as [[Blaenau Ffestiniog]] and [[Bethesda, Wales|Bethesda]], [[Wales]] there are still many buildings wholly constructed of slate. Slates can also be set into walls to provide a rudimentary [[Damp proofing|damp-proof membrane]]. Small offcuts are used as [[Shim (spacer)|shims]] to level floor joists. In areas where slate is plentiful it is also used in pieces of various sizes for building walls and hedges, sometimes combined with other kinds of stone.
===Other uses===
Because it is a good [[Insulator (electricity)|electrical insulator]] and fireproof, it was used to construct early-20th-century [[electric switchboard]]s and [[relay]] controls for large [[electric motor]]s.<ref name=bowles1922>{{cite book |last1=Bowles |first1=Oliver |title=The Technology of Slate |date=1922 |publisher=U.S. Government Printing Office |url=https://books.google.com/books?id=9NQi1A_KW5cC}}</ref> Because of its thermal stability and chemical inertness, slate has been used for laboratory bench tops and for [[billiard table]] tops.
Slate was used by earlier cultures as [[whetstone (tool)|whetstone]] to hone knives,<ref>{{cite journal |last1=Taylor |first1=William B. |title=Whetstones Found in Southeastern Massachusetts |journal=Bulletin of the Massachusetts Archaeological Society |date=2009 |volume=70 |issue=2 |pages=79–80 |url=https://core.ac.uk/download/pdf/160503012.pdf#page=30 |archive-url=https://web.archive.org/web/20210628232253/https://core.ac.uk/download/pdf/160503012.pdf |archive-date=2021-06-28 |url-status=live |access-date=28 June 2021}}</ref><ref>{{cite journal |last1=Arbel |first1=Yoav |title=Miscellaneous Finds from the Magen Avraham Compound, Yafo (Jaffa) |year=2020 |journal='Atiqot |volume=100 |pages=363–372 |jstor=26954598}}</ref> but whetstones are nowadays more typically made of quartz.<ref>{{cite web |url=http://www.popularwoodworking.com/article/what-is-an-oilstone-2 |title=What is an Oilstone? |last=Adam Cherubini |date=12 October 2011 |publisher=Popular Woodworking magazine |access-date=22 February 2017}}</ref> In 18th- and 19th-century schools, slate was extensively used for [[Chalkboard|blackboards]] and individual [[Slate (writing)|writing slates]], for which slate or chalk pencils were used.<ref name="bowles1922" /> In modern homes slate is often used as table coasters.
In areas where it is available, high-quality slate is used for [[tombstones]] and commemorative tablets.<ref>{{cite journal |last1=Born |first1=Anne |title=Blue Slate Quarrying in South Devon: An Ancient Industry |journal=Industrial Archaeology Review |date=November 1988 |volume=11 |issue=1 |pages=51–67 |doi=10.1179/iar.1988.11.1.51}}</ref> In some cases slate was used by the ancient [[Maya civilization]] to fashion [[Maya stelae|stelae]].<ref>{{cite journal |last1=Healy |first1=Paul F. |last2=Awe |first2=Jaime J. |last3=Iannone |first3=Gyles |last4=Bill |first4=Cassandra |title=Pacbitun (Belize) and ancient Maya use of slate |journal=Antiquity |date=June 1995 |volume=69 |issue=263 |pages=337–348 |doi=10.1017/S0003598X00064735|s2cid=162523022 }}</ref> Slate was the traditional material of choice for black [[Go (game)|Go]] stones in Japan, alongside [[Mollusc shell|clamshell]] for white stones. It is now considered to be a luxury.<ref>{{cite book|last=Fairbairn|first=John|title=The Go Player's Almanac|publisher=Kiseido Publishing Company|year=1992|isbn=978-4-906574-40-7|editor-last=Bozulich|editor-first=Richard|edition=2nd|publication-date=2001|pages=142–155|chapter=A Survey of the best in Go Equipment}}</ref>
Pennsylvania slate is widely used in the manufacture of turkey calls used for hunting turkeys.  The tones produced from the slate, when scratched with various species of wood striker, imitates almost exactly the calls of all four species of [[wild turkey]] in North America: eastern, Rio Grande, Osceola and Merriam's.
<gallery>
File:Betjeman memorial.JPG|[[John Betjeman]]'s grave with inscription on slate in Cornwall
File:Leonard Bramer - Mors Thriumphans.jpg|[[Leonard Bramer]], painting ''Mors Triumphans'' (oil on slate)
File:GoldsworthySlateCone.JPG|"Slate Cone" in [[Royal Botanic Garden Edinburgh]]
</gallery>
==Extraction==
{{Main|Slate industry}}
[[File:bergwerk-fell-hoffnung.jpg|thumb|The [[Fell Exhibition Slate Mine]] in [[Rhineland-Palatinate]], Germany]]
[[File:bergwerk-fell-stollen2.jpg|thumb|The historical Vogelsberg 1 pit at Fell Exhibition Slate Mine]]
[[File:Mules carrying slate. Dharamsala.jpg|thumb|Mules carrying slate roof tiles on their backs in [[Dharamshala]], India, in 1993]]Slate is found in the [[Arctic]] and was used by [[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. Deposits of slate exist throughout Australia, with large reserves quarried in the [[Adelaide Hills]] in [[Willunga, South Australia|Willunga]], [[Kanmantoo, South Australia|Kanmantoo]], and the [[Mid North]] at [[Mintaro, South Australia#Slate and Flagstone|Mintaro]] and [[Spalding, South Australia|Spalding]]. Slate is abundant in [[Brazil]], the world's second-largest producer of slate, around [[Papagaios]] in [[Minas Gerais]], which extracts 95 percent of Brazil's slate. However, not all "slate" products from Brazil are entitled to bear the [[CE marking|CE mark]].<ref>Fundación Centro Tecnológico de la Pizarra. Report into the "Technical properties of Bambui Slate from the State of Minas Gerais (Brazil) to ascertain its compliance with the Standard EN12326". [http://www.spanishslateuk.com/pdf/Brazilian_slate_summary.pdf Brazilian Slate Report] {{webarchive|url=https://web.archive.org/web/20100214213924/http://www.spanishslateuk.com/pdf/Brazilian_slate_summary.pdf |date=14 February 2010 }}, retrieved on 27 January 2010</ref>[[File:Mintaro Slate Quarry 1880.jpeg|thumb|Workers mining slate at Mintaro Quarry in [[Mintaro, South Australia]], {{Circa|1880}}]]
Most slate in Europe today [[Slate industry in Spain|comes from Spain]], the world's largest producer and exporter of natural slate, and 90 percent of Europe's natural slate used for roofing originates from the slate industry there. Lesser slate-producing regions in present-day Europe include [[Slate industry in Wales|Wales]] (with UNESCO landscape status and a [[National Slate Museum|museum at Llanberis]]), [[Cornwall]] (famously the village of [[Delabole]]), [[Cumbria]] (see [[Burlington Slate Quarries]], [[Honister Slate Mine]] and [[Skiddaw Slate]]) and, formerly in the West Highlands of Scotland, around [[Ballachulish]] and the [[Slate Islands, Scotland|Slate Islands]] in the [[United Kingdom]]. Parts of [[France]] ([[Duchy of Anjou|Anjou]], [[Loire Valley]], [[Ardennes]], [[Brittany]], [[Savoie]]) and [[Belgium]] (Ardennes), [[Liguria]] in northern [[Italy]], especially between the town of [[Lavagna]] (whose name is inherited as the term for ''chalkboard'' in [[Italian language|Italian]]) and Fontanabuona valley; [[Portugal]] especially around [[Valongo]] in the north of the country. [[Germany]]'s [[Moselle River]] region, [[Hunsrück]] (with a former mine open as a museum at [[Fell Exhibition Slate Mine|Fell]]), [[Eifel]], [[Westerwald]], [[Thuringia]] and north [[Bavaria]]; and [[Alta (town)|Alta]], [[Norway]] (actually [[schist]], not a true slate). Some of the slate from Wales and Cumbria is colored slate (non-blue): purple and formerly green in Wales and green in Cumbria.
In North America, slate is produced in [[Newfoundland (island)|Newfoundland]], eastern [[Pennsylvania]], [[Buckingham Slate|Buckingham County, Virginia]], and the Slate Valley region in [[Vermont]] and [[New York (state)|New York]], where colored slate is mined in the [[Granville (town), New York|Granville, New York]], area. A major slating operation existed in [[Monson, Maine]], during the late 19th and early 20th centuries, where the slate is usually dark purple to blackish, and many local structures are roofed with slate tiles. The roof of [[St. Patrick's Cathedral, New York|St. Patrick's Cathedral]] in [[New York City]] and the headstone of [[John F. Kennedy]]'s gravesite in [[Arlington National Cemetery]] are both made of Monson slate.<ref>[http://www.granville-ny.com/facts.htm Granville: Facts] {{webarchive|url=https://web.archive.org/web/20110108054330/http://www.granville-ny.com/facts.htm |date=8 January 2011 }} accessed 23 March 2011</ref>
==See also==
*[[Bluestone#South Australia|Bluestone in South Australia]], a form of slate used extensively in Adelaide 1850s–1920s
==References==
{{Reflist|33em}}
==Further reading==
* Page, William (ed.) (1906). ''The Victoria History of the County of Cornwall''; vol. I. (Chapter on quarries.) Westminster: Constable.
* Hudson, Kenneth (1972). ''Building Materials''; "Chapter 2: Stone and Slate". pp London: Longman, pp.&nbsp;14–27. {{ISBN|0-582-12791-2}}.
==External links==
{{Commons category}}
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* [http://www.aditnow.co.uk/ AditNow]—Photographic database of mines
* [http://www.slatevalleymuseum.org/ Granville Slate Museum]
* [http://quarriesandbeyond.org/articles_and_books/pdf/Howers%20Lightning%20Slate%20Reckoner%201888%20-%201904.pdf ''Hower’s Lightning Slate Reckoner''] (1884/1904), by F. M. Hower, Cherryville, Penn., on Stone Quarries and Beyond (PDF/18.95 MB)
* [http://www.stoneroof.org.uk/historic/Historic_Roofs/Slate_taxonomy.html Stone Roofing Association (U.K.) website with detailed information about stone roofing]
*{{Cite journal |last=Pierpont |first=Robert N. |title=Slate Roofing |journal=[[APT Bulletin]] |volume=19 |issue=2 |year=1987 |pages=10–23 |doi=10.2307/1494158 |jstor=1494158}}
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{{Stonemasonry}}
{{Rock type}}
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