
[Middle English sclate, from Old French esclate, splinter, feminine of esclat. See slat.]
For more information on slate, visit Britannica.com.
Any of the deformed fine-grained, mica-rich rocks that are derived primarily from mudstones and shales, containing a well-developed, penetrative foliation that is called slaty cleavage. Slaty cleavage is a secondary fabric element that forms under low-temperature conditions (less than 540°F or 300°C), and imparts to the rock a tendency to split along planes. It is a type of penetrative fabric; that is, the rock can be split into smaller and smaller pieces, down to the size of the individual grains. If there is an obvious spacing between fabric elements (practically, greater than 1 mm), the fabric is called spaced. Slates typically contain clay minerals (for example, smectite), muscovite/illite, chlorite, quartz, and a variety of accessory phases (such as epidote or iron oxides). Under increasing temperature conditions, slate grades into phyllite and schist. See also Argillaceous rocks; Clay minerals; Phyllite; Schist; Shale.
Slaty cleavage is defined by a strong dimensional preferred orientation of clay in a very clay rich, low-grade metamorphic rock, and the resulting rock is a slate. Slaty cleavage tends to be smooth and planar. Coupled with the penetrative nature of slaty cleavage, these characteristics enable slates to split into very thin sheets. This and the durability of the rock are reasons why slates are used in the roofing industry, in the tile industry, and in the construction of pool tables.
Idioms beginning with slate:
slated for, be
In addition to the idiom beginning with slate, also see clean slate.
A weak sedimentary rock, easily split along thin layers of bedding, formed by the compression of shales by the overlying rocks.
A hard, brittle metamorphic rock consisting mainly of clay minerals, characterized by good cleavage along parallel planes; used extensively as dimension stone in thin sheets for flooring, roofing, panels (both decorative and electrical), and chalkboard, and in granular form as surfacing on composition roofing.

|
|
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2009) |
| Metamorphic rock | |
Slate |
|
| Composition | |
|---|---|
| Primary | quartz, muscovite/illite |
| Secondary | biotite, chlorite, hematite, pyrite |
Slate is a fine-grained, foliated, homogeneous 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. When expertly "cut" by striking with a specialized tool in the quarry, many slates will form smooth flat sheets of stone which have long been used for roofing and floor tiles and other purposes. 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. Ninety percent of Europe's natural slate used for roofing originates from Spain.[1]
The word "slate" is also used for some objects made from slate. It may mean a single roofing slate, or a writing slate, traditionally a small piece of slate, often framed in wood, used with chalk as a notepad or noticeboard etc., and especially for recording charges in pubs and inns. The phrase "clean slate" or "blank slate" comes from this use.
|
Contents
|
Before the mid-19th century, the terms slate, shale and schist were not sharply distinguished.[2] In the context of underground coal mining, the term slate was commonly used to refer to shale well into the 20th century.[3] For example, roof slate refers to shale above a coal seam, and draw slate refers to roof slate (shale) that falls from the mine roof as the coal is removed.[4]
Slate is mainly composed of quartz and muscovite or illite, often along with biotite, chlorite, hematite, and pyrite and, 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.
Slate can be made into roofing slates, which are installed by a slater. Slates are often erroneously called shingles, as shingles made from stone are technically tiles. 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 easily stackable.
Slate is particularly suitable as a roofing material as it has an extremely low water absorption index of less than 0.4%. Its low tendency to absorb water also makes it very resistant to frost damage and breakage due to freezing.
Slate roof tiles are usually fixed using either nail fixing, or the hook fixing method as is common with Spanish slate. In the UK, nailing is typically done with double nails onto timber battens (England and Wales) or nailed directly onto timber sarking boards (Scotland and Northern Ireland). Nails will traditionally be copper, although modern alloy and stainless steel alternatives are known. Both these methods, if used properly, will provide a long-lasting weathertight roof with a typical lifespan of around 80–100 years.
Some mainland European slate suppliers suggest that using hook fixing means that [5]:-
The metal hooks are, however, visible and may be unsuitable for historic properties.
Slate tiles are often used for interior and exterior flooring, stairs, walkways and 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 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 Bethesda, Wales there are still many buildings wholly constructed of slate. Slates can also be set into walls to provide a rudimentary damp-proof membrane. Small offcuts are used as 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. In modern homes slate is often used as table coasters.
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. 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 slate or chalk pencils were used.
In areas where it is available, high-quality slate is used for tombstones and commemorative tablets. In some cases slate was used by the ancient Maya civilization to fashion stelae.
Slate-producing regions in Europe include Wales (see slate industry in Wales), Cornwall (famously the village of Delabole), Cumbria (see Burlington Slate Quarries, Honister Slate Mine and Skiddaw Slate) in the United Kingdom; parts of France (Anjou, Loire Valley, Ardennes, Brittany, Savoie); Belgium (Ardennes); 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; Spain see Slate Industry in Spain; Germany's (Moselle River-region, Hunsrück, Eifel, Westerwald, Thuringia and north Bavaria); Alta, Norway (actually schist not a true slate) and Galicia. Some of the slate from Wales and Cumbria is colored slate (non-blue): purple and formerly green in Wales and green in Cumbria. China has vast slate deposits; in recent years its export of finished and unfinished slate has increased, it has slate in various colors.
Slate is abundant in Brazil (the second-biggest producer of slate) around Papagaios in Minas Gerais (responsible for 95% of the extraction of slate in Brazil). An independent report by Consultant Geologist J. A. Walsh describes how certain products originating from Brazil on sale in the UK, are not entitled to bear the CE mark.[6]
Other areas known for slate production are the east coast of Newfoundland, the Slate Belt of Eastern Pennsylvania, Buckingham County Virginia (Buckingham Slate), and the Slate Valley of Vermont and New York, where colored slate is mined in the Granville, New York area.
A major slating operation existed 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. The roof of St. Patrick's Cathedral was made of roofing slate from Monson, as was the headstone of John F. Kennedy.[7]
Slate is also found in the Arctic and was used by the Inuit to make the blades for ulus.
Because slate was formed in low heat and pressure, compared to a number of other metamorphic rocks, some fossils can be found in slate; sometimes even microscopic remains of delicate organisms.[8]
| Wikimedia Commons has media related to: Slate |
|
||||||||||||||||||||
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Dansk (Danish)
n. - skifer, skifertagsten, tavle, hinkesten
v. tr. - lægge skifertag på, sætte på liste, foreslå, beramme, forudbestemme
adj. - skifergrå, skifer-
idioms:
Nederlands (Dutch)
lei, leisteen, grijs, kandidatenlijst, kandideren, afkraken
Français (French)
n. - ardoise, (US) liste de candidature
v. tr. - couvrir (qch) d'ardoises, (GB) taper sur, blâmer, (US, Pol) mettre (qn) sur la liste, (US) avoir de fortes chances de
adj. - d'ardoise
idioms:
Deutsch (German)
n. - Schiefer, Schiefertafel, Schieferplatte, Kandidatenliste
v. - vorsehen, scharf kritisieren
adj. - schiefergrau
idioms:
Ελληνική (Greek)
n. - (μαθητική) πλάκα, αβάκιο, (γεωλ.) σχιστόλιθος, (ΗΠΑ) λίστα υποψηφίων για αξίωμα
v. - καλύπτω (στέγη κ.λπ.) με πλάκες σχιστόλιθου, (ΗΠΑ) προετοιμάζω εκδήλωση, (ΗΠΑ) προτείνω κάποιον ως υποψήφιο, (Βρετ., καθομ.) επικρίνω, κατσαδιάζω
adj. - από πλάκες σχιστόλιθου
idioms:
Italiano (Italian)
stroncare, ardesia, lavagna, lista dei candidati
idioms:
Português (Portuguese)
n. - ardósia (f), cinzento azulado (m), lousa (f)
v. - assentar, censurar, criticar
adj. - critico (m)
idioms:
Русский (Russian)
шиферная плитка, грифельная доска, шиферный сланец, список, программа (состязаний), аспидный цвет, разгромная рецензия, крыть шифером, заносить в список кандидатов, выдвигать для рассмотрения, назначать (на какое-то время), дать нагоняй, выпороть
idioms:
Español (Spanish)
n. - pizarra, lista de candidatos
v. tr. - echar una bronca, vapulear, castigar
adj. - de pizarra, pizarreño, apizarrado
idioms:
Svenska (Swedish)
n. - skiffer, takplatta, takskiffer, griffeltavla, skiffergrått, preliminär kandidatlista för ett val
v. - täcka med skiffer, skiffertäcka, göra ner, läxa upp, tufsa till, föreslå som kandidat, tillkännage, planera in, avtala, utsätta, förutbestämma
adj. - skiffergrå
中文(简体)(Chinese (Simplified))
板岩, 石片, 石板, 铺石板, 痛打, 责骂, 暗蓝灰色的, 含板岩的
idioms:
中文(繁體)(Chinese (Traditional))
n. - 板岩, 石片, 石板
v. tr. - 鋪石板, 痛打, 責罵
adj. - 暗藍灰色的, 含板岩的
idioms:
한국어 (Korean)
n. - 슬레이트, 짙은 청회색, (지명) 후보자 명부
v. tr. - (지붕을) 슬레이트로 이다, 후보자 명단에 올리다, 예정하다
adj. - 석판질의, 석판색
日本語 (Japanese)
n. - スレート, 粘板岩, スレート色, 候補者名簿, 石板
v. - スレートでふく, 候補者名簿に載せる, 予定する, 予定させる, 酷評する
العربيه (Arabic)
(الاسم) صخر يسهل قطعه ألى ألواح تكسى بها ألسقوف, لوح أردوازي للكتابه, سجل أعمال أو أحداث (فعل) يسجل ألاسماء, يكسو بألواح أردوازيه (صفه) مكسو بألواح أردوازيه
עברית (Hebrew)
n. - צפחה, רעף, לוח צפחה, רשימת מועמדים
v. tr. - כיסה ברעפים, הציע מועמדות, הועיד, תכנן, גינה, תקף, קטל
adj. - אפור-כחול, עשוי רעפים
If you are unable to view some languages clearly, click here.