Description | Aragonite, CaCO3, is less common than its polymorph, calcite. Samples from Morocco are readily available from mineral dealers. Most contain clusters of dark to light brown crystals. The sample shown here is darker than most. Calcite and aragonite, while having the same composition, have different crystal forms. Aragonite tends to form orthorhombic prisms, but twinning gives them a hexagonal cross section. This sample is 7 cm across. |