Analysis of the evolution of structural complexity of the Cu₂(OH)₃Cl polymorphs along the botallackite–atacamite–clinoatacamite Ostwald cascade of phases from the viewpoint of Shannon information-based complexity parameters shows that structural information increases during the transition from less stable to more stable phases. Among the three polymorphs, botallackite is the simplest, atacamite is intermediate, and clinoatacamite is the most complex. This agrees well with the Goldsmith’s simplexity rule and shows that complexity is a physically important parameter that characterizes crystallization in complex chemical systems. Consideration of the crystal structures of the Cu₂(OH)₃Cl polymorphs in terms of their Cu–Cl arrays shows that transformation between the phases involves breaking and formation of chemical bonds and therefore has a reconstructive character.