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[[Image:Four of the Seven Sisters.jpg|thumb|200px|Four of the "Seven Sisters" along the [[Sussex]] coast, [[England]]]]

[[Image:Four of the Seven Sisters.jpg|thumb|200px|Four of the "Seven Sisters" along the [[Sussex]] coast, [[England]]]]

'''Chalk''' is a white, sedimentary rock, composed of [[calcium carbonate]]. One of its most dramatic outcrops is along the south coast of [[England]] where it forms the "white cliffs of [[Dover]]" and the Seven Sisters.

'''Chalk''' is a white, sedimentary rock, composed of [[calcium carbonate]]. The calcium carbonate originates from the calcareous liths deposited by blooms of species of [[coccolithophore]] [[phytoplankton]].

One of the most dramatic outcrops of chalk is along the south coast of [[England]] where it forms the "white cliffs of [[Dover]]", the Seven Sisters and parts of Englands [[Jurrasic Coast]], now a [[World Heritage Site]] in reckognition of its unusual geology.

Nowadays, chalk has been replaced by other substances. For example, the "chalk" that is used in blackboard writing or in sidewalk chalk is actually [[gypsum]].

As a useful commodity, chalk has been replaced by other substances. For example, the "chalk" that is used in blackboard writing or in sidewalk chalk is actually [[gypsum]].

[[Category:Sedimentary Rocks]]

[[Category:Sedimentary Rocks]]