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Slate

Slate

Overview

Slate is a fine-grained, foliated
Foliation (geology)
Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic belts. Rocks exhibiting foliation include the standard sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and...

, homogeneous metamorphic rock
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...

 derived from an original shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

-type sedimentary rock
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

 composed of clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

 or volcanic
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 ash through low-grade regional metamorphism
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...

. The result is a foliated
Foliation (geology)
Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic belts. Rocks exhibiting foliation include the standard sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and...

 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.
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Slate is a fine-grained, foliated
Foliation (geology)
Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic belts. Rocks exhibiting foliation include the standard sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and...

, homogeneous metamorphic rock
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...

 derived from an original shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

-type sedimentary rock
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

 composed of clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

 or volcanic
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 ash through low-grade regional metamorphism
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...

. The result is a foliated
Foliation (geology)
Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic belts. Rocks exhibiting foliation include the standard sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and...

 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
North Wales
North Wales is the northernmost unofficial region of Wales. It is bordered to the south by the counties of Ceredigion and Powys in Mid Wales and to the east by the counties of Shropshire in the West Midlands and Cheshire in North West England...

 can be found in many shades of grey, from pale to dark, and may also be purple, green or cyan
Cyan
Cyan from , transliterated: kýanos, meaning "dark blue substance") may be used as the name of any of a number of colors in the blue/green range of the spectrum. In reference to the visible spectrum cyan is used to refer to the color obtained by mixing equal amounts of green and blue light or the...

. Slate is not to be confused with shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

, from which it may be formed, or schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...

. Ninety percent of Europe's natural slate used for roofing originates from Spain
Slate Industry in Spain
90% of Europes's natural slate used for roofing originates from the slate industry in Spain , with the region of Galicia being the primary source of production....

.

The word "slate" is also used for some objects made from slate. It may mean a single roofing slate, or a writing slate
Slate (writing)
A writing slate is a piece of flat material used as a medium for writing.In the 19th century, writing slates were made of slate, which is more durable than paper and was cheap at the time when paper was expensive. It was used to allow children to practice writing...

, 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.

Historical mining terminology


Before the mid-19th century, the terms slate, shale and schist were not sharply distinguished. In the context of underground coal mining
Coal mining
The goal of coal mining is to obtain coal from the ground. Coal is valued for its energy content, and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from iron ore and for cement production. In the United States,...

, the term slate was commonly used to refer to shale well into the 20th century. 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.

Mineral composition


Slate is mainly composed of quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 and muscovite
Muscovite
Muscovite is a phyllosilicate mineral of aluminium and potassium with formula KAl22, or 236. It has a highly-perfect basal cleavage yielding remarkably-thin laminæ which are often highly elastic...

 or illite
Illite
Illite is a non-expanding, clay-sized, micaceous mineral. Illite is a phyllosilicate or layered alumino-silicate. Its structure is constituted by the repetition of tetrahedron – octahedron – tetrahedron layers. The interlayer space is mainly occupied by poorly hydrated potassium cations...

, often along with biotite
Biotite
Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula . More generally, it refers to the dark mica series, primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous endmembers...

, chlorite
Chlorite group
The chlorites are a group of phyllosilicate minerals. Chlorites can be described by the following four endmembers based on their chemistry via substitution of the following four elements in the silicate lattice; Mg, Fe, Ni, and Mn....

, hematite
Hematite
Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...

, and pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...

 and, less frequently, apatite
Apatite
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal...

, graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...

, kaolin, magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

, tourmaline
Tourmaline
Tourmaline is a crystal boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gem comes in a wide variety of colors...

, or zircon
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...

 as well as feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....

. Occasionally, as in the purple slates of North Wales
Slate industry in Wales
The slate industry in Wales began during the Roman period when slate was used to roof the fort at Segontium, now Caernarfon. The slate industry grew slowly until the early 18th century, then expanded rapidly until the late 19th century, at which time the most important slate producing areas were in...

, 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
Cleavage (geology)
This article is about rock cleavage, for cleavage in minerals see Cleavage Cleavage, in structural geology and petrology, describes a type of planar rock feature that develops as a result of deformation and metamorphism. The degree of deformation and metamorphism along with rock type determines the...

 of the specimen.

Uses


Slate in buildings


Slate can be made into roof
Roof
A roof is the covering on the uppermost part of a building. A roof protects the building and its contents from the effects of weather. Structures that require roofs range from a letter box to a cathedral or stadium, dwellings being the most numerous....

ing slates, also called roofing shingle
Roof shingle
Roof shingles are a roof covering consisting of individual overlapping elements. These elements are typically flat rectangular shapes laid in rows from the bottom edge of the roof up, with each successive higher row overlapping the joints in the row below...

s
, installed by a slater
Slater
Slater is an occupational surname of English origin. A slater is a tradesman.-Surname:* Allana Slater , Australian artistic gymnast* Bert Slater , Scottish football player* Bill Slater , English footballer...

. 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 :-
  • 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
  • Hook fixing is particularly suitable in regions subject to severe weather conditions since there is a greater resistance to wind uplift as the lower edge of the slate is secured.


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
Efflorescence
In chemistry, efflorescence is the loss of water of crystallization from a hydrated or solvated salt to the atmosphere on exposure to air.-Examples:...

, 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
Bethesda, Wales
Bethesda is a town lying on the River Ogwen and the A5 road on the edge of Snowdonia, in Gwynedd, north-west Wales, colloquially called Pesda by the locals.- History :...

 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.

Other uses



Because it is a good electrical insulator and fireproof
Fireproof
-Track List for Original 2002 Release:# "Fireproof" – 3:46# "Just 2 Get By" – 4:17# "Echelon" – 3:25# "Stay Up" – 3:40# "Behind Closed Doors" – 2:55# "Epidemic" – 3:14# "Hindsight" – 2:57# "Light at My Feet" – 3:28# "A Shame" – 3:17...

, it was used to construct early-20th century electric switchboard
Electric switchboard
An electric switchboard is a device that directs electricity from one source to another. It is an assembly of panels, each of which contains switches that allow electricity to be redirected. The U.S...

s and relay
Relay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...

 controls for large electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

s. 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
Chalkboard
A chalkboard or blackboard is a reusable writing surface on which text or drawings are made with sticks of calcium sulfate or calcium carbonate, known, when used for this purpose, as chalk. Chalkboards were originally made of smooth, thin sheets of black or dark grey slate stone...

 and individual writing slates
Slate (writing)
A writing slate is a piece of flat material used as a medium for writing.In the 19th century, writing slates were made of slate, which is more durable than paper and was cheap at the time when paper was expensive. It was used to allow children to practice writing...

 for which slate or chalk pencils were used.

In areas where it is available, high-quality slate is used for tombstones and commemorative tablets.

Slate extraction





In Eurasia


Slate-producing regions in Europe include Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

 (see slate industry in Wales
Slate industry in Wales
The slate industry in Wales began during the Roman period when slate was used to roof the fort at Segontium, now Caernarfon. The slate industry grew slowly until the early 18th century, then expanded rapidly until the late 19th century, at which time the most important slate producing areas were in...

), Cornwall
Cornwall
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...

 (famously the village of Delabole
Delabole
Delabole is a large village in north Cornwall, England, UK. It is situated approximately two miles west of Camelford.The village of Delabole came into existence in the 20th century; it is named after the Delabole Quarry. There were three hamlets: Pengelly, Medrose and Rockhead...

), Cumbria
Cumbria
Cumbria , is a non-metropolitan county in North West England. The county and Cumbria County Council, its local authority, came into existence in 1974 after the passage of the Local Government Act 1972. Cumbria's largest settlement and county town is Carlisle. It consists of six districts, and in...

 (see Burlington Slate Quarries
Burlington Slate Quarries
Burlington Slate Quarries are located near Kirkby-in-Furness in Cumbria, England. The quarries have produced a characteristic blue-grey slate for hundreds of years, with large-scale production starting in the early 19th century, when the Cavendish family organised small-scale quarrying activities...

, Honister Slate Mine
Honister Slate Mine
The Honister Slate Mine is a group of slate mines and quarries located at the top of the Honister Pass in the Lake District in England. The earliest reference to quarrying at this location is from 1728.-History:...

 and Skiddaw Slate
Skiddaw Slate
Skiddaw slate is an early Ordovician metamorphosed sedimentary rock, as first identified on the slopes of Skiddaw in the English Lake District....

) in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

; parts of France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 (Anjou
Anjou
Anjou is a former county , duchy and province centred on the city of Angers in the lower Loire Valley of western France. It corresponds largely to the present-day département of Maine-et-Loire...

, Ardennes
Ardennes
The Ardennes is a region of extensive forests, rolling hills and ridges formed within the Givetian Ardennes mountain range, primarily in Belgium and Luxembourg, but stretching into France , and geologically into the Eifel...

, Brittany
Brittany
Brittany is a cultural and administrative region in the north-west of France. Previously a kingdom and then a duchy, Brittany was united to the Kingdom of France in 1532 as a province. Brittany has also been referred to as Less, Lesser or Little Britain...

, Savoie
Savoie
Savoie is a French department located in the Rhône-Alpes region in the French Alps.Together with the Haute-Savoie, Savoie is one of the two departments of the historic region of Savoy that was annexed by France on June 14, 1860, following the signature of the Treaty of Turin on March 24, 1860...

); Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...

 (Ardenne); Liguria
Liguria
Liguria is a coastal region of north-western Italy, the third smallest of the Italian regions. Its capital is Genoa. It is a popular region with tourists for its beautiful beaches, picturesque little towns, and good food.-Geography:...

 in northern Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

, especially between the town of Lavagna
Lavagna
Lavagna is a fishing port city of c. 13,000 inhabitants in the curving stretch of the Italian Riviera di Levante called the gulf of Tigullio, in the province of Genoa in Liguria. The borgo of Lavagna was an important Ligurian cultural center in the Middle Ages...

 (which means chalkboard in Italian
Italian language
Italian is a Romance language spoken mainly in Europe: Italy, Switzerland, San Marino, Vatican City, by minorities in Malta, Monaco, Croatia, Slovenia, France, Libya, Eritrea, and Somalia, and by immigrant communities in the Americas and Australia...

) and Fontanabuona valley; Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...

 especially around Valongo
Valongo
Valongo is a Portuguese municipality located in the District of Porto, the city population is 18,698, and the municipality is composed of 5 parishes, of which three are cities and has a total population of 97,814 inhabitants.The two most populous cities in the Valongo municipality are Ermesinde,...

 in the north of the country; Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

's (Moselle River
Moselle River
The Moselle is a river flowing through France, Luxembourg, and Germany. It is a left tributary of the Rhine, joining the Rhine at Koblenz. A small part of Belgium is also drained by the Mosel through the Our....

-region, Hunsrück
Hunsrück
The Hunsrück is a low mountain range in Rhineland-Palatinate, Germany. It is bounded by the river valleys of the Moselle , the Nahe , and the Rhine . The Hunsrück is continued by the Taunus mountains on the eastern side of the Rhine. In the north behind the Moselle it is continued by the Eifel...

, Eifel
Eifel
The Eifel is a low mountain range in western Germany and eastern Belgium. It occupies parts of southwestern North Rhine-Westphalia, northwestern Rhineland-Palatinate and the south of the German-speaking Community of Belgium....

, Westerwald
Westerwald
The Westerwald is a low mountain range on the right bank of the River Rhine in the German federal states of Rhineland-Palatinate, Hesse and North Rhine-Westphalia. It is a part of the Rhine Massif...

, Thuringia
Thuringia
The Free State of Thuringia is a state of Germany, located in the central part of the country.It has an area of and 2.29 million inhabitants, making it the sixth smallest by area and the fifth smallest by population of Germany's sixteen states....

 and north Bavaria
Bavaria
Bavaria, formally the Free State of Bavaria is a state of Germany, located in the southeast of Germany. With an area of , it is the largest state by area, forming almost 20% of the total land area of Germany...

); Alta, Norway
Alta, Norway
-Birdlife:For those interested in bird watching, the river outlet, known locally as Altaosen is well worth a visit. This tidal area is used as a stopover for many wetland species.-Transportation:...

 (actually schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...

 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.

In the Americas


Slate is abundant in Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

 (the second-biggest producer of slate) around Papagaios
Papagaios
Papagaio is a small town in Minas Gerais, Brazil. It has approximately 15,000 inhabitants and its economy is based on exports of slate.Papagaio is 150 kilometers away from the state capital, Belo Horizonte....

 in Minas Gerais
Minas Gerais
Minas Gerais is one of the 26 states of Brazil, of which it is the second most populous, the third richest, and the fourth largest in area. Minas Gerais is the Brazilian state with the largest number of Presidents of Brazil, the current one, Dilma Rousseff, being one of them. The capital is the...

 (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
CE mark
CE marking is a mandatory conformity mark for products placed on the market in the European Economic Area . With the CE marking on a product the manufacturer ensures that the product conforms with the essential requirements of the applicable EC directives...

.

Other areas known for slate production are the east coast of Newfoundland, the Slate Belt of Eastern Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...

, Buckingham County Virginia (Buckingham Slate
Buckingham Slate
Buckingham Slate refers to a specific type of slate quarried near Arvonia in Virginia. The Buckingham Slate Company is the only active quarry and manufacturer of slate in Virginia...

), and the Slate Valley of Vermont
Vermont
Vermont is a state in the New England region of the northeastern United States of America. The state ranks 43rd in land area, , and 45th in total area. Its population according to the 2010 census, 630,337, is the second smallest in the country, larger only than Wyoming. It is the only New England...

 and New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

, where colored slate is mined in the Granville, New York area.

A major slating operation existed in Monson, Maine
Monson, Maine
Monson is a town in Piscataquis County, Maine, United States. As of the 2000 census, the town had a population of 666. The town is located on Route 15 which is a somewhat major route north to the well known Moosehead Lake Region, to which Monson is sometimes considered a gateway...

, 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
St. Patrick's Cathedral, New York
The Cathedral of St. Patrick is a decorated Neo-Gothic-style Roman Catholic cathedral church in the United States...

 was made of roofing slate from Monson, as was the headstone of John F. Kennedy
John F. Kennedy
John Fitzgerald "Jack" Kennedy , often referred to by his initials JFK, was the 35th President of the United States, serving from 1961 until his assassination in 1963....

.

Slate is also found in the Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...

 and was used by the Inuit
Inuit
The Inuit are a group of culturally similar indigenous peoples inhabiting the Arctic regions of Canada , Denmark , Russia and the United States . Inuit means “the people” in the Inuktitut language...

 to make the blades for ulu
Ulu
An ulu is an all-purpose knife traditionally used by Eskimo women, both Yupik and Inuit. It is utilized in applications as diverse as skinning and cleaning animals, cutting a child's hair, cutting food and, if necessary, trimming blocks of snow and ice used to build an igloo...

s.

Fossils



Because slate was formed in low heat and pressure, compared to a number of other metamorphic rock
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...

s, some fossils can be found in slate; sometimes even microscopic
Microscopic
The microscopic scale is the scale of size or length used to describe objects smaller than those that can easily be seen by the naked eye and which require a lens or microscope to see them clearly.-History:...

 remains of delicate organisms.

See also

  • List of rock types
  • Shale
    Shale
    Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

  • Tile
    Tile
    A tile is a manufactured piece of hard-wearing material such as ceramic, stone, metal, or even glass. Tiles are generally used for covering roofs, floors, walls, showers, or other objects such as tabletops...

  • National Slate Museum
  • Fell Exhibition Slate Mine
    Fell Exhibition Slate Mine
    The Fell Exhibition Slate Mine is a former slate mine in Germany located about 20 km east from Trier and about 60 km east of Luxembourg near the villages Fell and Thomm. The exhibition mine can be visited every day from April to October...

  • Slate industry in Wales
    Slate industry in Wales
    The slate industry in Wales began during the Roman period when slate was used to roof the fort at Segontium, now Caernarfon. The slate industry grew slowly until the early 18th century, then expanded rapidly until the late 19th century, at which time the most important slate producing areas were in...

  • Slate and stylus
    Slate and stylus
    The slate and stylus are tools used by blind persons to write text that they can read without assistance. Invented by Charles Barbier and Louis Braille as the tool for "writing" Braille, the slate and stylus allow for a quick, easy, convenient and constant method of making embossed printing for...

  • Slate Industry in Spain
    Slate Industry in Spain
    90% of Europes's natural slate used for roofing originates from the slate industry in Spain , with the region of Galicia being the primary source of production....


Further reading

  • Hudson, Kenneth (1972). Building Materials; "Chapter 2: Stone and Slate". London: Longman, pp. 14–27. ISBN 0582127912.

External links