Crystal-chemical considerations on eight metamorphic epidotes

The crystal structures of eight natural samples belonging to the clino-zoisite-epidote series were refined. Close correlations were found between either the b cell dimension or the M 3-O bond length or the intensities of some reflections and the chemical composition of the samples (Fe3+ contents increasing in the M3 site). Some brief considerations have been made upon the possible relations between the physical and chemical conditions of formation of the host-rocks and the geometrical variations occurring in the crystal structures of the epidotes