# Portable Raman Spectrometer for In Situ Analysis of Asbestos and Fibrous Minerals
## 2 Materials and Methods
### Raman Investigation  
Raman in situ measurements were carried out with a portable Enspectr RaPort(r) Raman spectrometer (pRS), a 'pistol-like' handheld instrument weighing 2.1 kg, equipped with a thermoelectrically cooled silicon Charge-Coupled Device and a 532-nm laser at a maximum output power of 30 mW. The laser spot is nearly 0.5 mm (Figure S1, Supplementary Material). Raman spectra were obtained in the extended wavenumber range 100-4000 cm\({}^{-1}\) with a spectral resolution of 8 cm\({}^{-1}\). The instrument is controlled remotely via a USB 2.0 cable connected to a laptop. It allows the operator to select settings for measurements, including more detailed power output selection, number of accumulations, and long accumulation times. The spectra were collected in a single acquisition up to 60 s. The instrument calibration was checked against the position of the bands of reference materials before each set of measurements. A working time up to 6 h at temperatures between 0 \({}^{\circ}\)C and 40 \({}^{\circ}\)C is recommended. For a comparison with other portable Raman instruments, see [PERSON] et al. (2017) [52].  
Figure 1: Mining sites. (**a**) Serpentine quarry at Valmalenco (central Alps, northern Italy); (**b**) Ni-open pit of Tontouta (Massif du sud, New Caledonia).  
Figure 2: Petrographic and morphological (SEM images) description of representative NOA-bearing samples. Optical photomicrographs (cross-polarized light images on the left) and SEM images (on the right) showing: (**a,b**) Valmalenco quarry. Veins of slip long-fiber chrysotile; (**c,d**) Balangero mine. Veins of slip chrysotile; (**e,f**) Balangero mine. Bundle of balangeroite fibers; (**g,h**) Tontoutua Ni-open pit. Bundle of chrysotile and fibrous antigorite; and (**i,l**) Tontouta Ni-open pit. Bundle of tremolite fibers. Abbreviations: Ctl, chrysotile; Blg, balangeroite; Atg, antigorite; Tr, tremolite.  
High-resolution micro-Raman (HRS) spectra were acquired on rock fragments and petrographic thin sections in nearly backscattering geometry with a Horiba Jobin-Yvon LabRam apparatus, equipped with an Olympus microscope with 10\(\times\), 50\(\times\), Ultra-Long Working Distance 50\(\times\), and 100\(\times\) objectives and a motorized x-y stage, and a holographic grating with 1800 lines/mm. The 473.1-nm line of a doubled Nd: YAG diode pumped laser was used as excitation; laser power was controlled by means of a series of density filters to avoid heating effects. The minimum lateral resolution was about 1 \(\upmu\)m (with the 100\(\times\) objective); the depth resolution was set to a few microns by means of a confocal hole. The spectral resolution was about 4 cm\({}^{-1}\). The system was calibrated using the 520.7 cm\({}^{-1}\) Raman peak of silicon before each experimental session. In addition, in the high wavenumber range, spectra were constantly calibrated using spectral lamps. Spectra were collected using the 100\(\times\) objective with repeated acquisition: 5 acquisitions for 30 s and 15 for 10 s in the low and high wavenumber spectral range, respectively.  
The background subtraction on each spectrum was performed with LabSpec(r) software.