Aragonite is one of two important natural calcium carbonate (CaCO3) minerals, the other and major variety being calcite (a third very rare variety is vaterite) aragonite and calcite can be formed by physical-chemical and by 'biological' (skeleton and shell forming) processes. 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 forms stalactites and other aggregates, such as the botryoidal (grapelike) precipitate in this example, also known as pisolithic. This sample is from a cave in Oujda, Morocco, actual height is 260 mm.