AN EPR STUDY OF THE GREEN DOLOMITE FROM MALENTRATA (ITALY)

In the carbonate mineralization associated to the magnesite mine of Malentrata (Pomarance, Pisa, Italy), one of the few occurrences worldwide of the rare green dolomite variety is reported. The occurrence of green dolomite is relatively uncommon and has attracted the attention of naturalists and scientists for many years. This is primarily due to its fascinating features which differentiate it from other varieties. There is a paucity of literature on this variety. We undertook a multimethodical study to gain a deeper insight into the unusual structural and chemical properties of the green dolomite from Malentrata. In the present contribution, we report the results of an electron paramagnetic resonance (EPR) study carried out on a green dolomite sample with the aim of approaching a comprehensive assessment of the crystal chemistry of the minor paramagnetic transition metal ions (TMI) incorporated into the dolomite structure. The investigations were carried out at X-band and under cryogenic conditions ranging from the liquid nitrogen up to room temperature. We were able to describe a complex cation speciation, dominated by the presence of both Mn(II) and Fe(III) species distributed over different structural and mineralogical hosts. We will propose a thorough discussion of the crystal chemical interpretation of the EPR evidence, linking in particular the occurrence of specific TMI with the overall unusual structural properties of the Malentrata dolomite variety.