Box with white "Cactus" Aragonite from northern Mexico.

The mineral aragonite is a calcium carbonate CaCO3 with chemical formula. It is an unstable polymorph of calcite, and it is therefore difficult to distinguish from calcite, because most of the properties are equal. By means of a color test, a distinction can be made: with a Feigl solution is aragonite black, whereas calcite remains colorless. Moreover, it is slightly harder than aragonite and calcite can be determined by a scratch test to which mineral is involved. A third distinction method is the habitus: aragonite usually grows in needle-shaped crystals (acicular), while calcite has a leaf-shaped habit. Using powder is the difference rather to unequivocally because aragonite has an orthorhombic structure and not as a trigonal calcite. Aragonite is always formed at a low temperature near the earth's surface. Aragonite is found in geysers, hot springs, caves, as oölieten in shallow seas, shells and pearls. Sites in Europe, Aragon (Spain), Limousis (France), Girgenti (Sicily), Bilin (Bohemia) and Eisenertz (Austria).