Crystal chemistry and structure of Lizardite-1T in serpentinite rocks from the Northern Apennine ophiolites (Modena Province).

We investigated the crystal-chemical features of six crystals of lizardite-1T sampled in four outcrops of ophiolite, atPompeano, Sassomorello, Varana, and Santa Scolastica, in the Modena Apennines, Italy. In spite of the extensive contributionsalready present in the literature, this is the first study dealing with lizardite from the Modena ophiolites. As is clear from one ofour samples, the whole-rock composition affects the composition of lizardite, which makes it susceptible to overprinting by latermetasomatic events. In our study, we paid particular attention to the effects of VIMg–1VIFe2+ and of IVSi–1 IVAl VI(Mg, Mn, Fe)2+–1VI(Al, Cr, Fe)3+ exchange mechanisms on the structure. Our results suggest that VIMg–1VIFe2+ substitution induces an increase inthe M–O4 length in octahedra and a decrease in the octahedral-site distortion. Both these effects are also observed to influencethe unit-cell parameter c. The effect of the IVSi–1 IVAl VI(Mg, Mn, Fe)2+–1 VI(Al, Cr, Fe)3+ substitution is to decrease the M–O1distance and concomitantly, to increase the T–O1 distance.