Chalk ( /ˈtʃɔːk/) is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates (coccoliths) shed from micro-organisms called coccolithophores. It is common to find chert or flint nodules embedded in chalk. Chalk can also refer to other compounds including magnesium silicate and calcium sulfate.

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 porous it can hold a large volume of ground water, providing a natural reservoir that releases water slowly through dry seasons.

Read more about Chalk:  Deposits, Formation, Composition, Uses

Other articles related to "chalk":

Southerham Grey Pit
... Southerham Grey Pit exposes nearly the entire Chalk Marl and the lower half of the Grey Chalk (Cenomanian) and is the only inland section of these beds ... the single most important section in the Cenomanian Chalk Marl and Grey Chalk in western Europe ... The Lewes area has long been famous for the exceptional diversity of the fossil fish found in its Chalk pits ...
Liquid Chalk
... The term liquid chalk refers to several substances, in relation to dry, powdery chalk liquid-chalk marking pens (with water-soluble ink) liquid-chalk mixtures for rock climbing and ... Despite the term using the word "chalk", there might be no actual chalk within some forms of "liquid chalk" mixtures ...
Liquid Chalk - Sports
... Liquid chalk can be a variation of the normal chalk (see magnesium carbonate) used to improve grip for sports such as rock climbing, weight lifting, or gymnastics ... Uses Rock climbers use liquid chalk to prevent their hands from sweating in situations where normal chalk or pof are inadequate ... - some bouldering problems take longer than normal chalk can hold, so in these cases liquid chalk can be used ...
Selma Group
... group is composed of, in ascending order, the Mooreville Chalk Formation, Demopolis Chalk Formation, Ripley Formation, and Prairie Bluff Chalk Formation ...
Chalk, Kent - History
... Chalk, already known in the 8th century from a witan (a Saxon meeting) held here, is mentioned in the Domesday Book ... Chalk's major claim to fame is its connection with Charles Dickens ... In 1935 Chalk parish became part of the Municipal Borough until then it had been a somewhat remote village ...

Famous quotes containing the word chalk:

    The women cry,
    Come, my fox,
    heal me.
    I am chalk white
    with middle age
    so wear me threadbare....
    Anne Sexton (1928–1974)

    No matter how much faculty of idle seeing a man has, the step from knowing to doing is rarely taken. ‘Tis a step out of the chalk circle of imbecility into fruitfulness.
    Ralph Waldo Emerson (1803–1882)

    Go, birds of spring: let winter have his fee;
    Let a bleak paleness chalk the door,
    So all within be livelier than before.
    George Herbert (1593–1633)