Abstract

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

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