Blue Aragonite from Argentina (40-60mm) rare

The mineral aragonite is a calcium carbonate with the chemical formula CaCO3. It is an unstable polymorph of calcite and is therefore difficult to distinguish from calcite because most of its properties are the same. A distinction can be made by means of a color test: with a Feigl solution, aragonite turns black, while calcite remains colorless. In addition, aragonite is slightly harder than calcite and can be determined via a scratch test which mineral it is. A third method of distinction is the habit: aragonite usually grows in needle-shaped crystals (acicular), while calcite has a leaf-shaped habit. The difference can be clearly determined using powder diffraction because aragonite has an orthorhombic structure and not a trigonal one like calcite. Aragonite is always formed at low temperatures near the Earth's surface. Aragonite is found in geysers, hot springs, caves, as oolites in shallow seas, in shells and in pearls. Locations in Europe are Aragón (Spain), Limousis (France), Girgenti (Sicily), Bilin (Bohemia) and Eisenertz (Austria).