HOME
The Info List - Chalk


--- Advertisement ---



Chalk
Chalk
( /ˈtʃɔːk/) is a soft, white, porous, sedimentary carbonate rock, a form of limestone composed of the mineral calcite. 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
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
Flint
is often deposited around larger fossils such as Echinoidea
Echinoidea
which may be silicified (i.e. replaced molecule by molecule by flint). Chalk
Chalk
as seen in Cretaceous
Cretaceous
deposits of Western Europe
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
Limestone
or the Jurassic oolitic limestones. This presumably indicates very stable conditions over tens of millions of years.

"Nitzana Chalk
Chalk
curves" situated at Western Negev, Israel
Israel
are chalk deposits formed in the Mesozoic
Mesozoic
era's Tethys Ocean

Chalk
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
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.

Contents

1 Mining 2 Deposits 3 Formation 4 Composition 5 Uses

5.1 Previous uses

6 See also 7 References 8 External links

Mining[edit]

Former underground chalk mine in Meudon, France

Main article: Chalk
Chalk
mining Chalk
Chalk
is mined from chalk deposits both above ground and underground. Chalk mining
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.[citation needed] Deposits[edit] The Chalk Group
Chalk Group
is a European stratigraphic unit deposited during the late Cretaceous
Cretaceous
Period. It forms the famous White Cliffs of Dover
White Cliffs of Dover
in Kent, England, as well as their counterparts of the Cap Blanc Nez
Cap Blanc Nez
on the other side of the Dover Strait. The Champagne region
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
Jasmund National Park
in Germany
Germany
and at Møns Klint
Møns Klint
in Denmark
Denmark
– both once formed a single island. Formation[edit] Ninety million years ago what is now the chalk downland of Northern Europe
Europe
was ooze accumulating at the bottom of a great sea. Chalk
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 sea-water. 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. Composition[edit] The chemical composition of chalk is calcium carbonate, with minor amounts of silt and clay.[1] 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. Uses[edit] 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
Blackboard
chalk manufacture now may utilize 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".[2] 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 out of gypsum.[3]

Open chalk pit, Seale, Surrey, UK

Child drawing with sidewalk chalk

Chalk
Chalk
is a source of quicklime by thermal decomposition, or slaked lime following quenching of quicklime with water.[4] 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
Cissbury
are one such example, but perhaps the most famous is the extensive complex at Grimes Graves
Grimes Graves
in Norfolk. Woodworking joints
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
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
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.[5] Chalk
Chalk
can also be used as fingerprint powder. Previous uses[edit] 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. However, it is now usually made from talc (magnesium silicate). Chalk
Chalk
was also 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.[6] In gymnastics, rock-climbing, weight-lifting and tug of war, chalk — now usually magnesium carbonate — is applied to the hands and feet to remove perspiration and reduce slipping. Chalk
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.[7][8] 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.[9] See also[edit]

Chalk
Chalk
mining Blackboard Chalk
Chalk
carving Chalk
Chalk
line Clunch Flint French chalk Hill
Hill
figure Pastel Sanguine Sidewalk
Sidewalk
chalk List of types of limestone

References[edit]

^ Huxley, T. H. 1868. On a piece of chalk. Macmillan's Magazine http://aleph0.clarku.edu/huxley/CE8/Chalk.html ^ Thakker, M., Shukla, P. and Shah, D.O., 2015. Surface and colloidal properties of chalks: A novel approach using surfactants to convert normal chalks into dustless chalks. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 480, pp.236-244. ^ http://www.madehow.com/Volume-1/Chalk.html ^ Blount, Bertram (1990). Chemistry for Engineers and Manufacturers: Chemistry of manufacturing processes. University of Wisconsin – Madison.  ^ Information on polishing powders, from the 1879 book "The Workshop Companion" ^ http://www.rsc.org/learn-chemistry/content/filerepository/CMP/00/001/020/TeacherResource%20Weightlifting.pdf?v=1356513839795 ^ Walker, Peter; et al. (2005). Rammed earth: design and construction guidelines. Bracknell, England: Building Research Establishment. p. 5. ISBN 9781860817342.  ^ Whitaker, William (1872). Memoirs of the Geological Survey of Great Britain. 4. London: Longmans, Green. p. 389. OCLC 2531996.  ^ Easton, David (1996). The Rammed Earth House. White River Junction, VT: Chelsea Green Publishing. p. 15. ISBN 9780930031794. 

External links[edit]

Wikimedia Commons has media related to Chalk.

Chalk
Chalk
cliffs in the North of Ireland Chalk: Sedimentary
Sedimentary
rocks Chalk
Chalk
East: chalk landscape and geodiversity in t

.