An atypical occurrence of asbestiform sepiolite associated to aliphatic hydrocarbons from Sassello (Ligurian Apennines, Italy): mineral-petrographic characterization and possible
hazards
R. Giustetto*, L. Macaluso, G. Berlier, Y. Ganjkhanlou, L. Barale
An unusual occurrence of asbestiform sepiolite, filling veins in the antigorite serpentinites of the Voltri Unit, exposed in a borrow pit (nowadays reclaimed) in the Deiva forest, near Sassello (NW Italy), was characterized with an in-depth analytical approach, aimed at studying its crystal-chemistry and structure and evaluating its possible hazards for human health. To the naked eye, this sepiolite has an evident fibrous habit, with fibres apparently up to several cm long. When observed with optical microscopy and SEM-EDS, however, these macroscopic fibres proved to be made by bundles of thinner fibrils (average length > 100 μm; thickness ≈ 80 nm), with a crystal-chemistry consistent to that reported in literature. Dehydration of this sepiolite sample was
monitored through TGA and FT-IR, performed at increasing temperatures. The latter approach, in particular, evidenced presence of moderate amounts of aliphatic hydrocarbons – not yet thoroughly identified – somehow associated to the fibres. The refinement of the crystal structure, performed with the Rietveld method, showed no significant difference from the literature models, but a peculiar distribution of zeolitic H2O inside the framework nano-tunnels was observed. The
geological context suggests that the Sassello sepiolite precipitated from low-temperature
hydrothermal fluids, which were saturated in Mg and silica by a prolonged interaction with the host rocks (serpentinites and partly serpentinized lherzolites). The same setting favoured formation of the associated abiotic hydrocarbons, by means of the Fischer-Tropsch reaction. The extremely long and flexible fibrils of this sepiolite specimen (length/width aspect ratio >> 3, as inspected by SEM) could represent a serious hazard for human health if air dispersed and breathed. In addition, its atypical association with hydrocarbons (only once reported in the literature: Giustetto et al., 2014) might even favour further fragmentation in thinner units, thus increasing its potential noxiousness.
Keywords: sepiolite, aliphatic hydrocarbons, Fischer-Tropsch-type reaction, hydrothermal system, noxiousness hazard.
Giustetto R., Seenivasan, K., Belluso, E. 2014. Asbestiform sepiolite coated by aliphatic
hydrocarbons from Perletoa, Aosta Valley Region (Western Alps, Italy): characterization, genesis and possible hazards. Mineralogical Magazine, 78(4), 919-940.
