DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Aragonite is one of two important natural calcium carbonate (CaCO3) minerals, the other and major one being calcite (a third very rare variety is vaterite) Aragonite differs from calcite by its crystal system, which is orthorhombic, while calcite is trigonal. Aragonite can be crystalline, with needle shaped crystals or pseudo-hexagonal and columnar forms, but is also found in pisolites, stalactites and other carbonate aggregates, as well as in massive deposits. Colours range from white to red and yellow-orange. Aragonite is the predominant shell and skeleton forming mineral of molluscs and corals. It is unstable on the long term and replaced by calcite, as is the case in most fossilized organisms. This large chunk is taken from a massive sedimentary deposit that has been deformed by tectonic movements when buried at greater subsurface depth. From China.
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