Retrograde serpentinized peridotites, belonging to the Internal Liguri
d terrains, occur in eastern Elba island, Italy The mesh texture (with
pyroxene bastites) is the typical textural arrangement. The mesh rims
are apparently fibrous, with negative optical elongation; cores range
from isotropic to microgranular. Optical and chemical determinations
indicate harzburgite (75 % olivine and 25 % pyroxene) as the protolith
for Elba serpentinites, with characteristics similar to mantle perido
tites from ocean basins. Microstructural analysis, led by transmission
electron microscopy, indicates that the mesh rims, rather than being
actually fibrous, consist of elongated lizardite crystals, having shar
p triangular sections with apices pointing toward the mesh center; poo
rly crystallized material occurs in between adjacent lizardite sectors
. The mesh cores consist of lizardite, chrysotile and polygonal serpen
tine, intermixed in variable amount and random mutual orientation. Bas
tites are generally poorly crystalline, formed by tiny lizardite lamel
lae with minor chrysotile. Mesh rims and cores have chemical compositi
ons variable from specimen to specimen, but almost constant within eac
h specimen; cores are always aluminium-enriched with respect to the ri
ms; when present, nickel (after olivine) occurs in the meshes. Bastite
s are chemically simpler than meshes, and, independently from their op
tical appearance, always have an aluminium-rich composition; chromium
(after pyroxene) always characterizes bastites. Chemical data indicate
absence of long range chemical fluxes during serpentinization. The fo
rmation of the mesh texture (with bastites) is explained as a two-stag
e process. In stage I, the peridotite undergoes thermal fracturing and
lizardite flakes start to decorate the pseudocubic fracture pattern (
thus producing the mesh rim). Massive water arrival into the weakened
peridotite induces stage III where serpentinization is completed formi
ng the mesh cores and bastites. In stage I the reaction is thermodynam
ically controlled, in stage II the reaction is kinetically controlled.