In recent years, the high incidence of harmful health effects through inhalation of airborne asbestos from amphibole-bearing rock me´langes has been thoroughly documented. Here, we present a field-based, multi-scale\ud geological approach aimed at illustrating the occurrence of\ud amphibole fibrous mineralisation in an ophiolitic suite from\ud the Ligurian Alps (Italy) and discussing the implication on\ud in situ determination of the asbestos hazard. The rock\ud mélange is composed of plurimetre-sized blocks of different lithotypes (metagabbro, serpentinite, chloritoschist)\ud juxtaposed by the meaning of tectonic structures. The geological-structural survey revealed that the fibrous mineralisation is localised in specific structural sites of the rock volume, including veins and schistosity. Both microchemical and crystal structure analyses on selected fibrous samples revealed that actinolite fibres grow in veins within the metagabbro and in chloritoschists, while fibrous tremolite occurs in serpentinite schistosity. The morphological features of these amphibole fibres have been analysed in TEM images and used for classifying them as ‘‘asbestiform’’ or ‘‘non-asbestiform’’. The results show that the asbestos hazard determination is not unequivocally identified when different procedures for asbestos fibre identification and classification are applied. This may have impact on normatives and regulations in defining environmental hazards due to asbestos occurrence

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Key indicators: single-crystal X-ray study; T = 293 K; mean (S-O) = 0.003 Å; R factor = 0.034; wR factor = 0.080; data-to-parameter ratio = 29.4. inorganic compounds i164 # 2007 International Union of Crystallography

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Abstract. In recent years, many studies have addressed the effect on human health caused by asbestos exposures. As asbestos is a group of fibrous minerals that mainly occurs in mafic and ultramafic rocks (ophiolitic sequences), a close relationship between asbestos occurrence and the geological history of host rocks should be expected. By reviewing the existing literature and presenting characteristic examples, it is proposed a direct correspondence exists between the presence of fibrous minerals in ophiolites and the rock fabric systematics due to the combined activity of deformation, metamorphism/metasomatism, and rock/fluid interaction. Understanding the geological factors that may be at the origin of the nucleation/growth of fibrous minerals constitutes a necessary requirement for developing a methodological and analytical procedure to evaluate asbestos hazard (A H ) in the natural prototype (ophiolitic rocks). A parameterisation of the A H in function of the main geological processes that produce the rock fabric systematics in different tectonic/geodynamic settings is discussed. A geological multidisciplinary approach (based on geological-structural field evidence combined with textural, mineralogical, petrological, and geochemical investigations) is proposed as the prerequisite for the evaluation of A H in natural environments. This approach, in particular, can provide a robust basis to formulate a procedural protocol finalised to the mitigation of asbestos effects in environments where these effects are still a real threat.

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