Contrasting chemical compositions in associated lizardite and chrysotile in veins from Elba, Italy

Serpentinitic veins consisting of associated chrysotile and well crystallized lizardite were extensively sampled in the Monte Fico quarries, Elba Island, Italy. The veins are mostly formed of euhedral lizardite-1T. After optical, IR and X-ray characterization, the specimens were studied by transmission electron microscopy. TEM provides evidence for the occurrence of chrysotile, polygonal serpentine and lizardite, with microstructural relations pointing to a continuous recrystallization from chrysotile to polygonal serpentine and to lizardite. No major fault structure occurs in lizardite. Chemical data indicate the existence of a compositional gap between lizardite [mean composition (Mg2.79Fe2+ 0.09 Fe3+ 0.07Al0.07)Σ=3.02(Si 1.91Al0.09)Σ=2.00 O5 (OH)3.90] and chrysotile [mean composition (Mg2.80Fe0.11Al0.06) Σ=2.97Si2.00 O5 (OH)4] with lizardite systematically enriched in aluminum and iron with respect to chrysotile. Therefore, the two minerals should no longer be considered as polymorphs.