# Portable Raman Spectrometer for In Situ Analysis of Asbestos and Fibrous Minerals
## 3 Results and Discussion
### Evaluation of the Performance of pRS
In the case of finely intermixed phases (Figure 5 and Supplementary Material S5), the superimposed contributions due to the Raman scattering of antigorite and chrysotile phases were clearly observed (Supplementary Material S5). At low-wavenumbers, the spectrum was dominated by the Raman bands associated with chrysotile, even if the occurrence of the shoulder at 380 cm\({}^{-1}\) and the peaks at 625 and 1045 cm\({}^{-1}\) suggested the presence of antigorite phase. At higher wavenumbers, the doublet associated with OH-stretching vibrations showed an intermediate shape between chrysotile and antigorite varieties. When multiple phases occurred, simply increasing the number of acquisitions may ensure the detection not only of the main mineralogical phase but also the occurrence of secondary phases present in minor amounts. \begin{table}
\begin{tabular}{c c} \hline \hline
**Portable Equipment** & **Micro-Raman** \\ \hline on bundles of fibers & on thin section \\ on an irregular surface & on a polished surface \\ pre-set measuring conditions & optimal measuring conditions \\ laser source 532 nm (green) & laser source 473.1 nm (blue) \\ spatial resolution 1 mm & spatial resolution 1–2 μm \\ spectral resolution 8 cm\({}^{-1}\) & spectral resolution 4 cm\({}^{-1}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Working conditions of portable Raman device (on the left) compared to benchtop high-resolution micro-Raman spectrometer (on the right). Figure 4: Comparison of Raman spectra of (**a**) chrysotile; (**b**) antigorite; (**c**) tremolite, and (**d**) balangerotite collected with portable Raman (on the top) and micro-Raman spectrometer (on the bottom). Taking into account the larger laser spot (about 1 mm, versus 1-2 mm of HRS) and the lack of rigid mount for positioning samples, the real spatial resolution of portable Raman was estimated in the order of a cubic millimeter. This could be a disadvantage when analyzing very small features, but it allows the detection of mixed-mineral varieties. This multi-site experimental approach evidenced that the main parameters that may affect the spectral quality of spectra collected with pRS are the possible difficulty of focusing the laser beam on non-cohesive and irregular surfaces and the fluorescence interference. According to [PERSON] et al. (2020), the nature of the matrix may affect the identification of asbestos and asbestos-like minerals. In the present study, the nature of rock fabric, consisting of massive to friable-powdered rocks formed by complex mineralogical associations (mixed aggregates of mineral fibers at the micro or sub-micro scale), slightly impacted the spectral quality. pRS was here proved to detect asbestos and asbestos-like mineral occurrences, also in limited amount and occurring in thin veins, in fractured and sheared areas of mines and pits. pRS is a promising tool to be used during the in situ phases of the assessment of the risk associated with naturally occurring asbestos and asbestos-like minerals. Mining activities, when operated in asbestos-bearing zones, can take advantage of pRS to identify asbestos occurrences during the front survey and consequently planning the mining operations.