## 4 The Example of the Green Stones
### The Raman Investigation
Generally speaking, by Raman spectroscopy, the higher the crystalline grade of the sample, the sharper are the scattered bands [65; 119]. Nevertheless, to obtain reliable Raman spectra on Green Stones, the analyst has to pay particular attention to the choice of laser source. While for inosilicates, and silicates generally, a visible red source (i.e., 632.8 nm) could be one of the best selections, due to the high affinity of the wavelength with the silicon tetrahedra vibration [120], when the phase is Cr-rich, a strong fluorescence issue can be generated. On the basis of this consideration, the availability of a second source, for example, a visible green (514.5/532 nm) or NIR (785 nm) laser, could be a good option to solve the issue and complete the characterization. The fluorescence issue is one of the main limits of the technique [65]. This problem might be solved changing the source but multi-laser systems are not always available. Finally, surface sample treatments (i.e., waxing, varnishing, etc.) can generate Raman fluorescences. Moreover, as previously mentioned, a potential difficulty could emerge in jadeite-pumpellyite identification, considering prudential tolerance of about 2 cm\({}^{-1}\) Raman shift for the spectrum interpretation, correlated with possible substitutions and/or crystal lattice defects, which are very common in natural phases [90]. In fact, these two phases diverge for only a 3 cm\({}^{-1}\) Raman shift on the main vibrational bands. In Figure 6, the reference Raman spectra of the two phases are reported. Despite the Raman shifts of the main vibrational bands being extremely close (700 vs. 697 cm\({}^{-1}\), see also Table 4), many differences can be highlighted by observing the trends of the entire spectra. The pumpellyite phase shows not only a spectrum richer in band numbers, but many of those bands are broader with respect to the jadeite ones, suggesting the presence of convoluted components [138]. Figure 5: Reference Raman spectra of several Green Stones samples. Kosmochlor spectrum is replotted from the RRUFF reference N. R120015 [127]; the other spectra have been acquired by In-Via Confocal micro-Raman Spectroscope, Renishaw, 514.5/632.8 nm sources and elaborated using Origin 2020 software by the author on GECI Reference stones collection. Circled bands in the serpentine spectrum are consistent with calcite phase associated with serpentine. Moreover, for the diagnosis, the texture must again be considered; in the top-left box of Figure 6, the OM of a cabochon section of jadeite-pumpellyite association is reported, showing the presence of many green elongated crystals of pumpellyite and jadeite in a white matrix. This texture, not associable with jadeite-jade gem quality, is a consequence of the specific genesis of the sample and produces higher brittlemess. From an operative point of view, Raman spectroscopy has several advantages. The last generation of portable Raman spectrometers, in particular, exhibit very high versatility and due to optical fiber technology, several models can be easily coupled with a portable microscope. These set-ups allow the Raman characterization of Green Stones \"on-site\" by a micro-Raman system, which is extremely useful in the case of non-homogenous samples. In 2017, [PERSON] et al. [139] reported that a portable Raman spectrometer was employed in situ inside the Centro-INAH Veracruz reserve; during the short time available for the analyses, several El Manati artifacts were analyzed with the main aim of verifying which artifacts were made of jade. By the application of this technique, the authors proved that a total of 11 artifacts, 10 axes, and 1 bead had been made by omphacite, instead of jadeite. Similarly, [PERSON] [140] reported the successful combination of a portable Raman system, applied with a portable XRF (PXRF) in a complementary way, for nephrite-jade artifacts characterization from the Cemetery of the Ying State (Henan Province, China).