Difference between revisions of "Chalk"
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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 | + | '''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 England's [[Jurassic Coast]], now a [[World Heritage Site]] in recognition of its unusual geology. | ||
| − | + | [[File:Chalk.jpg|thumb|left|200px|writing chalk]] | |
| + | As a useful commodity, chalk has been replaced by other substances.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]]. So, in common usage, chalk refers to a [[cylinder]]-shaped piece of gypsum that is used as a specialized writing implement. | ||
| − | [[Category:Sedimentary | + | [[Category:Sedimentary Rocks]] |
Latest revision as of 12:10, January 6, 2017
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 England's Jurassic Coast, now a World Heritage Site in recognition of its unusual geology.
As a useful commodity, chalk has been replaced by other substances.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. So, in common usage, chalk refers to a cylinder-shaped piece of gypsum that is used as a specialized writing implement.