Considerable work by Moreland and Padget (5) have shown that this dark layer is a member of the mineralogical group known as
pyroaurite. They form hexagonal plate crystals which tend to lay down as layered barrier films.
Pyroaurite and Sjogrenite [Mg.sub.6][Fe.sub.2.sup.3+](C[O.sub.3])(OH)[.sub.16] x 4[H.sub.2]O
We found pyroaurite at Ightem again in late 2005, as small hexagonal plates (XRD analysis by Paolo Orlandi, Pisa).
Traces of brucite were disclosed by XRD in altered serpentinite, with palygorskite, stevensite and pyroaurite.
Palygorskite occurs as fine-grained white material intergrown with pyroaurite, stevensite and brucite in altered serpentinite.
Pyroaurite [Mg.sub.6][Fe.sup.3+.sub.2]([CO.sub.3])[(OH).sub.16].4[H.sub.2]O
Pyroaurite occurs as fine-grained white material intergrown with playgorskite, stevensite and brucite in altered serpentinite.
Saponite occurs as fine-grained white material intergrown with pyroaurite, palygorskite and brucite in altered serpentinite.
(1980) La comblainite, nouveau mineral du groupe de ia
pyroaurite. Bulletin de Mineralogie, 103, 113-117.
(1981) Hydrohonessite - a new hydrated Ni-Fe hydroxyl-sulphate mineral; its relationship to honessite, carrboydite, and minerals of the
pyroaurite group.
(1981) Hydrohonessite--a new hydrated Ni-Fe hydroxy-sulphate mineral; its relationship to honessite, carrboydite and minerals of the
pyroaurite group.