The Aragonite reference article from the English Wikipedia on 24-Apr-2004
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Aragonite

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Aragonite is a polymorph of calcite, and shares its chemical composition CaCO3. Its structure, however, differs from calcite and leads to a different crystal shape. The type location for aragonite is Aragon, Spain.

It exists naturally in chitons' shells.

See also: list of minerals.

External link: Aragonite information