Chalk is a soft, white, porous, sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is an ionic salt called calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite shells (coccoliths) shed from micro-organisms called coccolithophores. Flint (a type of chert) is very common as bands parallel to the bedding or as nodules embedded in chalk. It is probably derived from sponge spicules or other siliceous organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified (i.e. replaced molecule by molecule by flint).
Chalk as seen in Cretaceous deposits of Western Europe is unusual among sedimentary limestones in the thickness of the beds. Most cliffs of chalk have very few obvious bedding planes unlike most thick sequences of limestone such as the Carboniferous Limestone or the Jurassic oolitic limestones. This presumably indicates very stable conditions over tens of millions of years.
Chalk has greater resistance to weathering and slumping than the clays with which it is usually associated, thus forming tall, steep cliffs where chalk ridges meet the sea. Chalk hills, known as chalk downland, usually form where bands of chalk reach the surface at an angle, so forming a scarp slope. Because chalk is well jointed it can hold a large volume of ground water, providing a natural reservoir that releases water slowly through dry seasons.
|Calcite (calcium carbonate)|
Chalk is mined from chalk deposits both above ground and underground. Chalk mining boomed during the Industrial Revolution, due to the need for chalk products such as quicklime and bricks. Some abandoned chalk mines remain tourist destinations due to their massive expanse and natural beauty.
The Chalk Group is a European stratigraphic unit deposited during the late Cretaceous Period. It forms the famous White Cliffs of Dover in Kent, England, as well as their counterparts of the Cap Blanc Nez on the other side of the Dover Strait. The Champagne region of France is mostly underlain by chalk deposits, which contain artificial caves used for wine storage. Some of the highest chalk cliffs in the world occur at Jasmund National Park in Germany and at Møns Klint in Denmark – both once formed a single island.
Ninety million years ago what is now the chalk downland of Northern Europe was ooze accumulating at the bottom of a great sea. Chalk was one of the earliest rocks made up of microscopic particles to be studied under the microscope, when it was found to be composed almost entirely of coccoliths. Their shells were made of calcite extracted from the rich seawater. As they died, a substantial layer gradually built up over millions of years and, through the weight of overlying sediments, eventually became consolidated into rock. Later earth movements related to the formation of the Alps raised these former sea-floor deposits above sea level.
The chemical composition of chalk is calcium carbonate, with minor amounts of silt and clay. It is formed in the sea by sub-microscopic plankton, which fall to the sea floor and are then consolidated and compressed during diagenesis into chalk rock.
Most people first encounter the word "chalk" in school where it refers to blackboard chalk, which was originally made of mineral chalk, since it readily crumbles and leaves particles that stick loosely to rough surfaces, allowing it to make writing that can be readily erased. Blackboard chalk manufacture now may use mineral chalk, other mineral sources of calcium carbonate, or the mineral gypsum (calcium sulfate). While gypsum-based blackboard chalk is the lowest cost to produce, and thus widely used in the developing world, calcium-based chalk can be made where the crumbling particles are larger and thus produce less dust, and is marketed as "dustless chalk". Colored chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often colored), used to draw on sidewalks, streets, and driveways, are primarily made of gypsum.
Chalk is a source of quicklime by thermal decomposition, or slaked lime following quenching of quicklime with water. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines, where the prime object was to remove flint nodules for stone tool manufacture. The surface remains at Cissbury are one such example, but perhaps the most famous is the extensive complex at Grimes Graves in Norfolk.
Woodworking joints may be fitted by chalking one of the mating surfaces. A trial fit will leave a chalk mark on the high spots of the corresponding surface. Chalk transferring to cover the complete surface indicates a good fit. Builder's putty also mainly contains chalk as a filler in linseed oil.
Chalk may be used for its properties as a base. In agriculture, chalk is used for raising pH in soils with high acidity. The most common forms are CaCO3 (calcium carbonate) and CaO (calcium oxide). Small doses of chalk can also be used as an antacid. Additionally, the small particles of chalk make it a substance ideal for cleaning and polishing. For example, toothpaste commonly contains small amounts of chalk, which serves as a mild abrasive. Polishing chalk is chalk prepared with a carefully controlled grain size, for very fine polishing of metals. Chalk can also be used as fingerprint powder.
Several traditional uses of chalk have been replaced by other substances, although the word "chalk" is often still applied to the usual replacements. Tailor's chalk is traditionally a hard chalk used to make temporary markings on cloth, mainly by tailors. It is now usually made of talc (magnesium silicate).
Chalk was traditionally used in recreation. In field sports, such as tennis played on grass, powdered chalk was used to mark the boundary lines of the playing field or court. If a ball hits the line, a cloud of chalk or pigment dust will be visible. In recent years, powdered chalk has been replaced with titanium dioxide. In gymnastics, rock-climbing, weightlifting and tug of war, chalk — now usually magnesium carbonate — is applied to the hands and feet to remove perspiration and reduce slipping.
Chalk may also be used as a house construction material instead of brick or wattle and daub: quarried chalk was cut into blocks and used as ashlar, or loose chalk was rammed into blocks and laid in mortar. There are still houses standing which have been constructed using chalk as the main building material. Most are pre-Victorian though a few are more recent.
The Battle of Chalk Bluff (also known as the Skirmish at Chalk Bluff) (May 1 – 2, 1863) was a military engagement of the American Civil War. The battle was fought near Chalk Bluff, northwest of St. Francis (present-day Clay County, Arkansas), where U.S. Brig. Gen. Wm. Vandever, commanding the Second Division of the Army of the Frontier, was repulsed in an attempt to prevent Marmaduke's Division from crossing the St. Francis River. Though a Confederate victory, Marmaduke suffered considerable casualties and his momentum had been checked, forcing him to abandon his second expedition into Missouri.Blackboard
A blackboard (also known as a chalkboard) 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. Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone.Calcareous grassland
Calcareous grassland (or alkaline grassland) is an ecosystem associated with thin basic soil, such as that on chalk and limestone downland. Plants on calcareous grassland are typically short and hardy, and include grasses and herbs such as clover. Calcareous grassland is an important habitat for insects, particularly butterflies, and is kept at a plagioclimax by grazing animals, usually sheep and sometimes cattle. Rabbits used to play a part but due to the onset of myxomatosis their numbers decreased so dramatically that they no longer have much of a grazing effect.
There are large areas of calcareous grassland in northwestern Europe, particularly areas of southern England, such as Salisbury Plain and the North and South Downs.
The machair forms a different kind of calcareous grassland, where fertile low-lying plains are formed on ground that is calcium-rich due to shell sand (pulverised sea shells).ChalkZone
ChalkZone is an American animated television series created by Bill Burnett and Larry Huber for Nickelodeon. The series follows Rudy Tabootie, an elementary school student whose magic chalk allows him into the ChalkZone, an alternate dimension where everything drawn on a blackboard and erased becomes real. The show concentrates on the adventures of Rudy, his sidekick Snap, and classmate, Penny Sanchez, within the Chalkzone.
ChalkZone originally aired as part of Fred Seibert's Oh Yeah! Cartoons animated shorts showcase in 1998. The series ran on Nickelodeon from March 22, 2002, through August 23, 2008, with 40 episodes in total. It was produced by Frederator Studios and Nickelodeon Animation Studio.Chalk Bluffs Natural Area
The Chalk Bluffs is a barren chalk escarpment in the northeastern part of the U.S. state of Colorado, stretching from the Wyoming border east of I-25 to near the South Platte River in Logan County and Weld County.Chalk Mountains (Colorado)
The Chalk Mountains are a mountain range in Archuleta County, Colorado.Cretaceous
The Cretaceous ( , kri-TAY-shəs) is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, and the longest period of the Phanerozoic Eon. The Cretaceous Period is usually abbreviated K, for its German translation Kreide (chalk, creta in Latin).
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.Cue sports
Cue sports (sometimes written cuesports), also known as billiard sports,
are a wide variety of games of skill generally played with a cue stick, which is used to strike billiard balls and thereby cause them to move around a cloth-covered billiards table bounded by elastic bumpers known as cushions.
Historically, the umbrella term was billiards. While that familiar name is still employed by some as a generic label for all such games, the word's usage has splintered into more exclusive competing meanings in various parts of the world. For example, in British and Australian English, "billiards" usually refers exclusively to the game of English billiards, while in American and Canadian English it is sometimes used to refer to a particular game or class of games, or to all cue games in general, depending upon dialect and context. In colloquial usage, the term "billiards" may be used colloquially to refer to pocket billiards games, such as pool, snooker, or Russian pyramid.
There are 3 major subdivisions of games within cue sports:
Carom billiards, referring to games played on tables without pockets, typically 10 feet in length, including balkline and straight rail, cushion caroms, three-cushion billiards, artistic billiards and four-ball
Pool, covering numerous pocket billiards games generally played on six-pocket tables of 7-, 8-, or 9-foot length, including among others eight-ball (the world's most widely played cue sport), nine-ball (the dominant professional game), ten-ball, straight pool (the formerly dominant pro game), one-pocket, and bank pool
Snooker, English billiards and Russian pyramid, games played on a billiards table with six pockets called a snooker table (which has dimensions just under 12 ft by 6 ft), all of which are classified entirely separately from pool based on a separate historical development, as well as a separate culture and terminology that characterize their play.There are other variants that make use of obstacles and targets, and table-top games played with disks instead of balls.
Billiards has a long and rich history stretching from its inception in the 15th century, to the wrapping of the body of Mary, Queen of Scots, in her billiard table cover in 1586, through its many mentions in the works of Shakespeare, including the famous line "let's to billiards" in Antony and Cleopatra (1606–07), and through the many famous enthusiasts of the sport such as: Mozart, Louis XIV of France, Marie Antoinette, Immanuel Kant, Napoleon, Abraham Lincoln, Mark Twain, George Washington, French president Jules Grévy, Charles Dickens, George Armstrong Custer, Theodore Roosevelt, Lewis Carroll, W.C. Fields, Babe Ruth, Bob Hope, and Jackie Gleason.Downland
A downland is an area of open chalk hills. This term is especially used to describe the chalk countryside in southern England. Areas of downland are often referred to as downs, deriving from a Celtic word for "hills".Garry Chalk
Garry Glen Chalk (born February 17, 1952) is a British-born Canadian actor and voice actor. He has provided the voices for Optimus Primal of Beast Wars: Transformers and Beast Machines, as well the Optimus Prime in the anime English dubs of Transformers: Armada, Transformers Energon, and Transformers: Cybertron, and also was the third American voice of Dr. Robotnik for Sonic Underground. He has lent his voice to over 30 animated television series and has been in films such as The Fly II, Godzilla and Freddy vs. Jason. He played the recurring role of Col. Chekov on Stargate SG-1. He is perhaps best known for his recurring role as Inspector Andrew Pawlachuk on Cold Squad.Magnesium carbonate
Magnesium carbonate, MgCO3 (archaic name magnesia alba), is an inorganic salt that is a white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals.Monroe, Connecticut
Monroe is an affluent town in Fairfield County, Connecticut, United States. The population was 19,479 at the 2010 census.Like many of its neighbors, Monroe is largely considered a bedroom community of New York City and Bridgeport. Monroe's neighbors are Easton, Newtown, Oxford, Shelton, and Trumbull.
The New York Times profiled Monroe in February 2013.North Downs
The North Downs are a ridge of chalk hills in south east England that stretch from Farnham in Surrey to the White Cliffs of Dover in Kent. Westerham Heights, at the northern edge of the North Downs, near Bromley, South London, is the highest point in London at an elevation of 245 m (804 ft). The North Downs lie within two Areas of Outstanding Natural Beauty (AONBs), the Surrey Hills and the Kent Downs. The North Downs Way National Trail runs along the North Downs from Farnham to Dover.Primrose Hill railway station
Primrose Hill was a railway station at Primrose Hill, in the London Borough of Camden, London, England.
It was opened on 5 May 1855 as Hampstead Road, replacing an earlier station of that name (opened 9 June 1851). It was renamed Chalk Farm on 1 December 1862 and became Primrose Hill on 25 September 1950. The station closed on 28 September 1992.Salisbury Plain
Salisbury Plain is a chalk plateau in the south western part of central southern England covering 300 square miles (780 km2). It is part of a system of chalk downlands throughout eastern and southern England formed by the rocks of the Chalk Group and largely lies within the county of Wiltshire, but also stretching into Berkshire and Hampshire. The plain is famous for its rich archaeology, including Stonehenge, one of England's best known landmarks. Largely as a result of the establishment of the Defence Training Estate Salisbury Plain (DTE SP), the plain is sparsely populated and is the largest remaining area of calcareous grassland in north-west Europe. Additionally the plain has arable land, and a few small areas of beech trees and coniferous woodland. Its highest point is Easton Hill.Sarah Chalke
Sarah Chalke (; born August 27, 1976) is a Canadian actress and voice artist. She is known for portraying Dr. Elliot Reid on the NBC/ABC comedy series Scrubs, the second Becky Conner and Andrea on the ABC sitcoms Roseanne and The Conners, Stella Zinman on the CBS sitcom How I Met Your Mother, and Beth Smith on Adult Swim's adult animated science-fiction series Rick and Morty. She also had a recurring role on the third season of the ABC/TBS sitcom Cougar Town.Simon in the Land of Chalk Drawings
Simon in the Land of Chalk Drawings is a British children's animated series about the adventures of a young child named Simon, who has a magic blackboard. Things that Simon draws on the chalkboard become real in the Land of Chalk Drawings, which Simon can enter by climbing over a fence near his home with a ladder. The stories often revolve around the unintended effects that Simon's drawings have on the Land of Chalk Drawings, such as when an upset Simon draws a picture of his angry self, which goes on a rampage.
The programme is based upon a series of four children's books by Edward McLachlan. It was produced in the mid 1970s by FilmFair Productions in London for Thames Television, and was originally a five-minute programme, broadcast around tea time in Britain. In the U.K., during the 1980s, the programme was shown during Pob's Programme on Channel 4. The programme also became familiar to American audiences in the mid-1970s when it was featured on Captain Kangaroo (where it was narrated by Bob Keeshan instead of Bernard Cribbins), later on Pinwheel, and after that, on Romper Room. In Canada, it was narrated by Ernie Coombs and shown on CBC Television, although TVOntario aired the British version.South Downs
The South Downs are a range of chalk hills that extends for about 260 square miles (670 km2) across the south-eastern coastal counties of England from the Itchen Valley of Hampshire in the west to Beachy Head, in the Eastbourne Downland Estate, East Sussex, in the east. The Downs are bounded on the northern side by a steep escarpment, from whose crest there are extensive views northwards across the Weald. The South Downs National Park forms a much larger area than the chalk range of the South Downs and includes large parts of the Weald.
The South Downs are characterised by rolling chalk downland with close-cropped turf and dry valleys, and are recognised as one of the most important chalk landscapes in England. The range is one of the four main areas of chalk downland in southern England.The South Downs are relatively less populated compared to South East England as a whole, although there has been large-scale urban encroachment onto the chalk downland by major seaside resorts, including most notably Brighton and Hove. The South Downs have been inhabited since ancient times and at periods the area has supported a large population, particularly during Romano-British times. There is a rich heritage of historical features and archaeological remains, including defensive sites, burial mounds and field boundaries. Within the South Downs Environmentally Sensitive Area there are thirty-seven Sites of Special Scientific Interest, including large areas of chalk grassland.The grazing of sheep on the thin, well-drained chalk soils of the Downs over many centuries and browsing by rabbits resulted in the fine, short, springy turf, known as old chalk grassland, that has come to epitomise the South Downs today. Until the middle of the 20th century, an agricultural system operated by downland farmers known as 'sheep-and-corn farming' underpinned this: the sheep (most famously the Southdown breed) of villagers would be systematically confined to certain corn fields to improve their fertility with their droppings and then they would be let out onto the downland to graze. However, starting in 1940 with government measures during World War II to increase domestic food production and continuing into the 1950s, much grassland was ploughed up for arable farming, fundamentally changing the landscape and ecology, with the loss of much biodiversity. As a result, while old chalk grassland accounted for 40-50% of the eastern Downs before the war, only 3-4% survives. This and development pressures from the surrounding population centres ultimately led to the decision to create the South Downs National Park, which came into full operation on 1 April 2011, to protect and restore the Downs.
The South Downs have also been designated as a National Character Area (NCA 125) by Natural England. It is bordered by the Hampshire Downs, the Wealden Greensand, the Low Weald and the Pevensey Levels to the north and the South Hampshire Lowlands and South Coast Plain to the south.The downland is a highly popular recreational destination, particularly for walkers, horseriders and mountain bikers. A long distance footpath and bridleway, the South Downs Way, follows the entire length of the chalk ridge from Winchester to Eastbourne, complemented by many interconnecting public footpaths and bridleways.The Caucasian Chalk Circle
The Caucasian Chalk Circle (German: Der kaukasische Kreidekreis) is a play by the German modernist playwright Bertolt Brecht. An example of Brecht's epic theatre, the play is a parable about a peasant girl who rescues a baby and becomes a better mother than its wealthy natural parents.
The play was written in 1944 while Brecht was living in the United States. It was translated into English by Brecht's friend and admirer Eric Bentley and its world premiere was a student production at Carleton College, Northfield, Minnesota, in 1948. Its first professional production was at the Hedgerow Theatre, Philadelphia, directed by Bentley. Its German premiere by the Berliner Ensemble was on October 7, 1954, at the Theater am Schiffbauerdamm in Berlin.The Caucasian Chalk Circle is one of Brecht's most celebrated works and one of the most regularly performed 'German' plays. It reworks Brecht's earlier short story "Der Augsburger Kreidekreis." Both derive from the 14th-century Chinese play The Chalk Circle by Li Xingdao.