Slate
Metamorphic rock | |
Composition | |
---|---|
Primary | quartz, muscovite/illite |
Secondary | biotite, chlorite, hematite, pyrite Specific gravity: 2.7 – 2.8,2.9 |
Slate is a fine-grained,
The foliation in slate, called "
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 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 "blank slate" come from this usage.
Description
Slate is a fine-grained, metamorphic rock that shows no obvious compositional layering but can easily be split into thin slabs and plates.
Slaty cleavage is continuous, meaning that the individual cleavage planes are too closely spaced to be discernible in hand samples. The
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
Slate is mainly composed of the minerals quartz,
Terminology
Before the mid-19th century, the terms "slate", "
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.[2]
Uses
Construction
Slate can be made into roofing slate, a type of 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 First World War following improvements in railway, road and waterway transportation systems.[17]
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.[18] Natural slate, which requires only minimal processing, has an embodied energy that compares favorably with other roofing materials.[19] 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,[20] often with little or no maintenance.[18] Natural slate is also fire resistant and energy efficient.[21]
Slate roof tiles are usually fixed (fastened) either with nails or with hooks (as is common with Spanish slate).[22] In the UK, fixing is typically with double nails onto timber battens (England and Wales)[23] or nailed directly onto timber sarking boards (Scotland and Northern Ireland).[citation needed] Nails were traditionally of copper, although there are modern alloy and stainless steel alternatives.[24] Both these methods, if used properly, provide a long-lasting weathertight roof with a lifespan of around 60–125 years.[18]
Some mainland European slate suppliers suggest that using hook fixing means that:[25]
- 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[26]
- 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.[26]
The metal hooks are, however, visible and may be unsuitable for historic properties.
Slate tiles are often used for interior and exterior flooring,[27] stairs,[28] walkways[29] and wall cladding.[30] Tiles are installed and set on mortar and grouted along the edges. Chemical sealants are often used on tiles to improve durability and appearance,[31] increase stain resistance,[27] reduce efflorescence, and increase or reduce surface smoothness. Tiles are often sold gauged, meaning that the back surface is ground for ease of installation.[31] 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
Other uses
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.[32] 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
In areas where it is available, high-quality slate is used for
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.
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John Betjeman's grave with inscription on slate in Cornwall
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Leonard Bramer, painting Mors Triumphans (oil on slate)
-
"Slate Cone" in Royal Botanic Garden Edinburgh
Extraction
Slate is found in the Arctic and was used by Inuit to make the blades for ulus. 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, Kanmantoo, and the Mid North at Mintaro and 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 mark.[39]
Most slate in Europe today
In North America, slate is produced in
See also
- Bluestone in South Australia, a form of slate used extensively in Adelaide 1850s–1920s
References
- ^ a b c d e Marshak, Stephen. Essentials of Geology (3rd ed.).[page needed]
- ^ a b Robertson, S. (1999). "BGS Rock Classification Scheme, Volume 2: Classification of metamorphic rocks" (PDF). British Geological Survey Research Report. RR 99-02. Archived (PDF) from the original on 3 April 2018. Retrieved 27 February 2021.
- ISBN 9780199653065.
- ^ ISBN 0922152349.
- ^ ISBN 0716724383.
- ISBN 0582300967.
- ISBN 0387904301.
- ISBN 9781107057647.
- ^ BBC Video: David Attenborough: Lost Worlds, Vanished Lives
- S2CID 140689763.
- ^ Yardley 1989, pp. 64, 170.
- .
- ^ Fossen 2016, p. 61.
- ^ Raymond, R. W. (1881). "Slate". A Glossary of Mining and Metallurgical Terms. American Institute of Mining Engineers. p. 78.
- ^ Fay, Albert H. (1920). "Slate". A Glossary of the Mining and Mineral Industry. United States Bureau of Mines. p. 622.
- ^ Weller, J. Marvin, ed. (1960). Supplement to the Glossary of Geology and Related Sciences. American Geological Institute. p. 18.
- ^ Schunck, Eberhard; Oster, Hans Jochen (2003). Roof Construction Manual Pitched Roofs (print ed.). Basel: De Gruyter. p. 12.
- ^ a b c Chavez, Mark (2013). "Should I Replace My Slate Roof with a Synthetic?". National Park Service. Retrieved 28 June 2021.
- .
- .
- ^ Natural Slate, the natural option Archived 10 March 2014 at the Wayback Machine
- ^ "Slate Design and Fixing Guide" (PDF). SSQ Group. Retrieved 28 June 2021.
- ^ "Natural roofing slate design and fixing guide" (PDF). SSQ Group. p. 8. Archived (PDF) from the original on 26 June 2019. Retrieved 28 June 2021.
- ^ "6 Basic Principals of Slate Roofing". National Slate Association. 3 August 2017. Retrieved 28 June 2021.
- ^ Galician and Spanish Slate website "Hook Fixing". Retrieved on 26 January 2010 archived
- ^ a b "Hook fixing" (PDF). SSQ Group. Archived (PDF) from the original on 26 June 2019. Retrieved 28 June 2021.
- ^ a b Taylor, Glenda; Vila, Bob (11 August 2016). "All You Need to Know About Slate Floors". bob vila. Action Media, Inc. Retrieved 28 June 2021.
- ^ Robinson, Kristy (2 July 2012). "Installing Slate Tiles on Front Stairs". SFGate. Hearst. Retrieved 28 June 2021.
- ^ "How to Lay a Walkway with Slate Pavers". doityourself. Retrieved 28 June 2021.
- ^ Asaff, Sarabeth (December 2013). "How to Install Exterior Slate Tile". SFGate. Hearst. Retrieved 28 June 2021.
- ^ a b Lewitin, Joseph. "Everything You Need to Know About Slate Flooring Tiles". The Spruce. Dotdash. Retrieved 28 June 2021.
- ^ a b Bowles, Oliver (1922). The Technology of Slate. U.S. Government Printing Office.
- ^ Taylor, William B. (2009). "Whetstones Found in Southeastern Massachusetts" (PDF). Bulletin of the Massachusetts Archaeological Society. 70 (2): 79–80. Archived (PDF) from the original on 28 June 2021. Retrieved 28 June 2021.
- JSTOR 26954598.
- ^ Adam Cherubini (12 October 2011). "What is an Oilstone?". Popular Woodworking magazine. Retrieved 22 February 2017.
- .
- S2CID 162523022.
- ISBN 978-4-906574-40-7.
- ^ 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". Brazilian Slate Report Archived 14 February 2010 at the Wayback Machine, retrieved on 27 January 2010
- ^ Granville: Facts Archived 8 January 2011 at the Wayback Machine accessed 23 March 2011
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. 14–27. ISBN 0-582-12791-2.
External links
- AditNow—Photographic database of mines
- Granville Slate Museum
- Hower’s Lightning Slate Reckoner (1884/1904), by F. M. Hower, Cherryville, Penn., on Stone Quarries and Beyond (PDF/18.95 MB)
- Stone Roofing Association (U.K.) website with detailed information about stone roofing
- Pierpont, Robert N. (1987). "Slate Roofing". JSTOR 1494158.