Aragonite is one of two important natural calcium carbonate (CaCO3) minerals, the other, and major variety, being calcite. Both 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, in pseudo-hexagonal columnar habitat, but also forms non-crystalline aggregates, such as the botryoidal (grapelike) variety in this example. Sample is from Ighoud in Central Morocco, actual length 310 millimetres.