Gli amianti in Val di Susa e le rocce che li contengono

The asbestos in the rocks of the Susa Valley (Torino Province, Piemonte, Italy). According to the Italian law, only six minerals are considered asbestos, i.e. chrysotile, actinolite, tremolite, anthophyllite, grunerite (commercial name: amosite), riebeckite (c.n.: crocidolite). Chrysotile belongs to the serpentine group, whereas the others to the amphibole group. For geologic reasons, in the western Alps the only chrysotile, actinolite and riebeckite asbestos may be found naturally. Usually the asbestos occur in the rocks as accessory minerals, but exceptionally they may be so abundant to make a true economic mineralization: the best example is that occurring in the northernmost end of the Lanzo Ultramafic Massif near Lanzo (western Alps), where the most important chrysotile asbestos deposit of the western Europe was mined until 1990. As a rule, the asbestos occurs as vein-filling minerals, and is released from the hosting rock either by natural physico-chemical alteration processes or by the human works. As to the asbestos-hosting rocks, chrysotile occurs in serpentinized ultramafics, whereas tremolite and actinolite may be found in a wider spectrum of lithologies belonging to the Piemonte zone of calcschists with metaophiolites. A systematic petrographic study of meta-ophiolites from the western Alps has allowed to find both new asbestiform minerals (e.g.: balangeroite and carlosturanite) and minerals, usually non fibrous, which locally occur with a fibrous habit (e.g.: diopside and Ti-clinohumite). Since many fibrous minerals are very similar under the optical microscope (OM) and often may occur intergrown even at submicroscopic scale, their unambiguous identification requires the joint use of more analytical techniques, such as OM, SEM-EDS, TEM-EDS, FTIR, XRPD, μ-FTIR, e μRaman spectroscopy.