On the diversity of pyroxene structure types

Although crystal structures of pyroxenes are built from such simple units as silicate chains and zigzag chains of cation octahedra, they exhibit an unexpected diversity, with many structure types readily transforming one into another following variations in composition, temperature or pressure.While the topology of pyroxene structures has been addressed in numerous studies, there is still a lack of a concise and convenient nomenclature suitable for routine use by mineralogists.Here, such a nomenclature is proposed based on a scheme of layer stacking.This requires neither any 'idealization' of real pyroxene structures into hypothetical close-packed ones, nor knowledge of advanced topological concepts.Hence, it can be widely used in mineralogical applications and educational purposes.A comprehensive graphical representation of the layer stacking in pyroxenes is also developed, suitable for analysis of symmetry, twinning and pathways of phase transitions.