CONTRASTING CHEMICAL-COMPOSITIONS IN ASSOCIATED LIZARDITE AND CHRYSOTILE IN VEINS FROM ELBA, ITALY

Serpentinitic veins consisting of associated chrysotile and well cryst allized 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, wit h microstructural relations pointing to a continuous recrystallization from chrysotile to polygonal serpentine and to lizardite. No major fa ult structure occurs in lizardite. Chemical data indicate the existenc e of a compositional gap between lizardite [mean composition .073+Al0. 07)(Sigma=3.02)(Si1.91Al0.09)(Sigma=2.00) O-5 (OH)(3.90)] and chrysoti le [mean composition Mg2.80Fe0.11Al0.06)(Sigma=2.97)Si-2.00 O-5 (OH)(4 )] with lizardite systematically enriched in aluminum and iron with re spect to chrysotile. Therefore, the two minerals should no longer be c onsidered as polymorphs.