# Portable Raman Spectrometer for In Situ Analysis of Asbestos and Fibrous Minerals
## 2 Materials and Methods  
### Description of Investigated Area  
To test the possible interference of rock fabric (i.e., matrix) on the diagnostic power of portable Raman, three different kinds of industrial exploitation sites occurring in different geological settings, namely an active serpentine quarry (Valmalenco, Italy; Figure 1a), a former asbestos chrysotile mine (Balangero mine, Italy), and an active Ni-ore lateritic deposit (Tontouta mine, New Caledonia, Figure 1b) have been selected. Particular attention was devoted to assessing if the degree of cohesion of hosted rocks (from massive serpentine to lateritic soil) and the presence of secondary phases (e.g., chlorite, saponite, diopside) in the mineralogical matrix should affect the quality of spectra.  
The Valmalenco area (central Alps, northern Italy, Figure 1a) is located at the Penninic to Austroalpine boundary zone, and the most important tectonic unit is the Malenco-Forno nappe, a huge ultramafic body (more than 130 km\({}^{2}\)) interpreted as a sub-continental mantle fragment [40,41]. The most common lithotype is represented by schistose antigoritic serpentines, consisting of antigorite, olivine, diopside, and minor magnetite and chlorite, and quarried as valuable dimension stone and marketed worldwide [42]. These serpentinites also host different industrial mineral deposits, ranging from talc lodes up to long-fiber chrysotile veins. Moreover, well-formed demantoid crystals, a Cr-rich variety of andradradite garnet, may occur in chrysotile veins [43]. Asbestos, which occurs in discrete cross-fiber and slip-fiber veins, gave rise in the past to widespread mining activity, particularly between the end of the XIX century and 1975, and was used mainly for weaving tablecloths or for wicks.  
The Balangero chrysotile mine (western Alps, Piedmont, northern Italy) was the biggest asbestos mine in Europe: the extraction started in 1923, peaking in the seventies and eighties (up to 1.5 \(\times\) 10\({}^{6}\) m\({}^{3}\) of tout-venant per year), and stopped definitively in 1990. The chrysotile mineralization (both cross-fiber and slip-fiber) is hosted by the ultramafites (upper mantle tectonics) of the Balangero body and the adjacent Lanzo massif (Internal Piedmontese Zone, Penninic Domain), partly re-equilibrated by the early-alpine high pressure-low temperature metamorphism (500-550 \({}^{\circ}\)C, 15 kb) into antigoritic serpentinites [44,45]. Therefore, two generations of chrysotile veins occur [46]. The first vein generation consists of long-fiber chrysotile (up to several centimeters in length). The second vein generation consists of short-fiber chrysotile (a few millimeters in length). Other fibrous minerals (e.g., balangeroite) are associated with chrysotile asbestos in the orebody.  
The Tontouta-Opoue open mine (Massif du Sud, southwest New Caledonia; Figure 1b) is set in Ni-rich lateritic deposits formed by pedogenesis of exposed ultramafic protoolith. Nilaterite deposits were formed during the Neogene by lateritic weathering of obducted and serpenized harzburgite-dunite peridotite [47, 48, 49, 50]. Serpentine minerals (chrysotile, fibrous antigorite) and minor tremolite-actinolite amphiboles are commonly hosted in lateritic and saprolitic zone currently mined [51]. As a consequence of pedogenetic processes, Caledonian samples show a peculiar strongly fibrous appearance. At the hand scale, rock fragments appear more friable and with a structureless aspect.