Paramorph - A pseudomorph involving two minerals with an identical composition but different crystal structures. The original mineral forms, but conditions then cause it to be unstable, so it transforms into the other mineral with the same chemical structure while retaining the original crystal shape. An example of this is Aragonite (CaCO₃ - Crystallizes in orthorhombic system) that becomes unstable and transforms into Calcite (CaCO₃ - Crystallizes in trigonal system), but retains the original orthorhombic shape.