Chalk (pronounced /tʃɔːk/) is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. It forms under relatively deep marine conditions from the gradual accumulation of minute calcite plates (coccoliths) shed from micro-organisms called coccolithophores. It is common to find flint and chert nodules embedded in chalk. Chalk can also refer to other compounds including magnesium silicate and calcium sulfate.
Chalk...
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Chalk (pronounced /tʃɔːk/) is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. It forms under relatively deep marine conditions from the gradual accumulation of minute calcite plates (coccoliths) shed from micro-organisms called coccolithophores. It is common to find flint and chert nodules embedded in chalk. Chalk can also refer to other compounds including magnesium silicate and calcium sulfate.
Chalk is resistant to erosion and slumping compared to 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.
Chalk has long been quarried in England, providing building material and marl for fields. In southeast England,...
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