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International audience; Asbestos consists in natural minerals crystallized in a specific habit and possessing in particular properties. In the case of Naturally Occurring Asbestos, usual methods applied to the identification of mineral fibers and the determination of their possible asbestiform nature seems not efficient, especially in the case of mineral fibers included in mineral matrix. We present a new in-situ method based on the use of confocal Raman-in-SEM imaging implemented in a Scanning Electron Microscope as an efficient method for in-situ mineralogy. The limitation of conventional methods is discussed. We applied 2D-Raman imaging to the identification of sub-micrometric fibers included in different mineral matrix. We were able to identify actinolite fibers down to 400 nm in diameter, included in feldspar, quartz and/or calcite matrix. Moreover, Confocal Raman allows the collection of 3D data that would provide access to critical information on the morphology of the amphibole fibers in the volume, such as aspect ratio, fibers distribution and amphibole volume fraction. We performed this method on various examples of rocks containing actinolite fibers of mean structural formula is: Na0,04-0,12Mg2,79-3,73Al0,29-0,58K0,01Ca1,79-1,98Mn0,01-0,09Fe 2+ 0,99-1,91Fe 3+ 0,12-0,25Si7,64-7,73O22(OH)2. We demonstrated that coupling confocal Raman imaging and SEM is a new and efficient in-situ method for identification and morphological characterization of amphibole fibers. Highlights New methods are requested for characterizing asbestos fibers in a mineral matrix SEM-Raman imaging is efficient for characterizing mineral fibers in-situ Confocal Raman imaging makes 3D analysis possible 3D analysis provides information on the aspect ratio and volume fraction of asbestos Fibers thinner than 400nm can be identified by confocal Raman in SEM ( = 532 nm)

Asbestos is a commercial term which refers to six minerals that crystallize as fibrous bundles made of very thin and easily separable fibrils. Asbestos fibers have been exploited for a long time and voluntary added in a very large set of manufactured products. In France, asbestos is prohibited since an official decree published in 1997 that prohibits the manufacture, processing, sale and import of asbestos. The asbestos ban has been the subject of an European directive published in 1999. Following this ban, a standard was defined in order to specify the sampling, preparation and identification methods for asbestos fibers in samples of commercial origin (ISO 22262-1). For natural materials, no specific analytical protocol is currently defined in France. Searching for asbestos in a rock sample, the commonly used protocols require the reduction of the sample, the grinding of a sub-sample (1 to 2 g) and its calcination in order to eliminate organic matter, then an acid attack to dissolve some constituents (calcite, gypsum). The final test portion (~ 20 mg) is mixed in water, stirred using ultrasound, filtered through a metallized membrane and covered with a new layer of carbon before it can be examined using a transmission electron microscope.The protocols currently used are long and complex and require the grinding of the sub-sample. This grinding operation is a critical step because it can lead, starting from non-asbestiform minerals, to the artificial formation of more or less fine and elongated fibriform particles (cleavage fragments), quite similar in some cases to asbestos fibers. Grinding is therefore an operation liable to affect the quality of the final diagnosis.The new protocol presented here was built with the aim of developing an analytical approach specific to coherent rock samples. This protocol does not involve the grinding of the sample and allows the in-situ morphological and chemical characterization of fibrous minerals. It is based on the use of combined analytical techniques (MOLP, EPMA, FESEM-EDS, FIB-SEM, and confocal RAMAN in SEM) from a single support corresponding to a polished thin section. This protocol allows to observe the natural morphologies of the fibers, to measure their dimensions, to characterize the relationships between fibers and the other mineralogical constituents while preserving the texture of the rock and to acquire precise chemical analyzes of the fibers. It also overcomes problems related to the grinding of the sample and the formation of cleavage fragments. This protocol has been tested through the study of several types of massive rock samples. It provides a representative and reliable in-situ diagnosis of the initial state of the fibers in solid rocks.

International audience; This paper provides a field description and an analytical characterization of the fibrous minerals associated with ultrabasic and basic rocks from the Corsican Ophiolitic Complex, on the island of Corsica, in order to examine their asbestos potential. Thirty-five fibrous samples taken from serpentinites, magnesium-rich meta-gabbros and meta-basalts were studied, using combined EPMA, Ramanand FESEM methods. The results highlight that naturally occurring asbestos (NOA) are abundant in serpentinites and regularly occur in magnesium-rich meta-gabbros and meta-basalts in northern Corsica. The spatial distribution, abundance and mineralogical types of these NOA strongly depend on the petrographic nature of the hosting rocks and their structural pattern. NOA in serpentinites correspond to chrysotile vein networks in the internal parts of the thickest rocky masses and to tremolite veins and shear planes carrying tremolite fibers, both in the external parts of these masses and in highly sheared serpentinites within or close to tectonic contacts. NOA in highly deformed magnesium-rich meta-gabbros are associated with the opening and filling of albite-tremolite veins, associated with the syntectonic boudinage of the most competent meta-gabbros. In the meta-basalts, NOA are associated with late metamorphic, actinolite-bearing polymineralic veins cross-cutting the foliation planes. Fragments and pebbles of serpentinites, meta-gabbros and meta-basalts containing NOA are also present in colluvium, scree and alluvium resulting from erosion processes. Special attention should be paid to serpentinites and/or magnesium-rich meta-gabbros-bearing colluvium in which fibrous occurrences of tremolite regularly evolved into whitish clusters consisting of very long, easily separable, flexible and entangled fibers with a higher asbestos potential. The characterization of NOA in the COC serpentinites, meta-gabbros and meta-basalts leads us to consider them as hazardous materials. As these lithologies are very abundant within the whole structural edifice, they may be regularly impacted by development or construction work and thus require suitable monitoring.

International audience; Asbestos consists of natural mineral fibers crystallized in a specific way with specific properties including flexibility, high tensile strength, resistance to heat and chemical degradation. The term asbestos refers to one fibrous serpentine, and five asbestiform varieties of amphiboles [1][2]. Asbestos is considered a Category 1 human carcinogen (e.g. [1][3][4][5][6]), as inhalation of asbestos fibers causes respiratory diseases, in particular asbestosis, lung cancers and malignant mesothelioma. Due to the pathogenicity of asbestos fibers, their use has been banned in most countries around the world. The classification as "asbestos" comprises three main characteristics: sub-micrometric fibrous morphology (so-called asbestiform), chemistry and crystallography (i.e. mineralogy). The ban applies to natural materials, which are quarried and used for public works projects. Compliance with existing rules requires accurate diagnosis of the asbestos or non-asbestos nature of the materials likely to be exploited in a quarry or involved in the opening of a construction site. Conventional methods for asbestos diagnosis, mainly based on the use of TEM, are hard to apply to massive materials as the sample preparation protocol is complex, it is likely to release artifacts like cleavage fragments, or sample-piece thinning is costly and hard to achieve and thus not applicable in routine analysis. The use of a LV-FE-SEM-EDS (Low vacuum field emission gun scannning electron microscope equiped with energy dispersive spectroscopy) coupled to confocal Raman-in-SEM imaging (RISE) is a new and efficient method for identifying the mineral nature of sub-micrometer fibers or fibrous bundles. SEM coupled to EDS provides a qualitative or semi-quantitative composition of the fiber. The crystal structure is determined by confocal Raman spectroscopy (with lateral resolution down to 360 nm [7]). Thus the combination of these two kinds of information allows for accurate identification of both the nature and the morphology of the mineral. The combination of SEM, EDS and confocal Raman imaging in a unique analytical system (RISE) allows precise location of the same area / fiber and identification of its mineral nature. In addition, RISE allows the acquisition of 3D data, which is able to provide morphological information of the mineral distribution in the sample volume and leading to the determination of the aspect ratio, a critical parameter for asbestos (i.e. asbestiform or non-asbestiform). Moreover, this combination of techniques is not destructive. The coupling of SEM-EDS with RISE is a powerful analytical system that simplifies and reinforces existing analytical procedures. For highest resolution studies of fibers in the sample volume (3 D imaging), the RISE can be connected to a FIB-SEM [7]. Although FIB volume reconstruction is a destructive method, the resolution of the voxel can be extended to below 100 nm [8] – a resolution sufficient for visualizing even the thinnest fibers. Furthermore, Raman 3D view is an efficient tool for sampling TEM slices using the FIB.

This paper provides new mineralogical and morphological characterizations of calcic amphiboles from hydrothermally altered dolerites from France to discuss their potential to contain naturally occurring asbestos (NOA) and to release elongated mineral particles corresponding to asbestos fibers, or asbestos-like fibers, into the air. The calcic amphiboles were characterized using electron microprobe analysis, scanning and transmission electron microscopy. The results underline that fibrous occurrences of actinolite and ferro-actinolite regularly occur in hydrothermally altered dolerites, both in the groundmass and in quartz veins. In the groundmass, actinolitic amphiboles crystallize at the expense of magmatic clinopyroxenes and are rarely fibrous. Conversely, actinolite and ferro-actinolite fibers from quartz veins are potentially asbestiform to clearly asbestiform. The identification of quartz veins in hydrothermally altered dolerites is, therefore, an important parameter which should draw attention to the possible presence of asbestiform actinolite fibers. The mineralogical characterization of such veins as well as the estimation of their thickness and density is an important point to consider during studies involving NOA issues. Moreover, the degree of weathering of the dolerites, which directly affects the ability of non-asbestiform actinolite crystals to dissociate into very thin fibers, regarded as cleavage fragments instead of as asbestos, is also a key parameter to consider. Hydrothermally altered dolerites are common rocks likely to be exploited by the quarrying industry to produce aggregates or to be affected by construction works. Due to the abundance of actinolite fibers that they may contain locally, these rocks become priority targets to be monitored in terms of geological characterization and airborne fiber emission to ensure the protection of populations and workers.