What is the difference between calcite crystals and aragonite crystals?

by The Library of Congress

Question by Bill 8634: What is the difference between calcite crystals and aragonite crystals?
The calcium usually is in the form of calcite crystals in marine (gastropod) species and aragonite crystals in terrestrial species.

Best answer:

Answer by kumorifox
The only difference lies in the crystal structure. Calcite is trigonal, whereas aragonite is orthorhombic. This phenomenon, where a single substance can crystallize in more than one type of crystal, is called polymorphism.

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