## 4 The Example of the Green Stones
### Chemical Characterization: Elemental Analyses  
The final information discussed in the present review consists of the chemistry and relative analytical techniques. For the chemical analyses of Green Stones, note the general chemical formula discussed previously in Table 3. The chemical analysis is not so significant for the phase identification, which can be easily carried out by other analytical techniques as previously discussed. Onthe other hand, elemental analysis is a deeper and complementary investigation, focusing on the origin of the color (natural or due to treatment), to be combined with UV-Vis/NIR information and which is extremely useful for geographic origin determination. This last factor is a very delicate discussion point, because the origin determination can be made not on the basis of the main elements common to all gemstones belonging to the same mineral phases but on trace elements quantification. Another factor which complicates the analysis interpretation is that Green Stones are typically composed of mineral associations, as previously discussed. Moreover, due to their characteristic genetic processes, involving metamorphic alterations, differences can be detected in the chemical traces of samples coming from different points of the same veins. To bypass this issue, or at least collect reliable information for origin identification, a systematic source characterization is beneficial. In this scenario, the first choice for elemental analysis is the ED-XRF technique, due to its non-destructive characteristics and the availability of the portable system, as previously discussed [78, 79]. For example, [PERSON] et al. [166] described the application of a portable XRF system (PXRF) for in situ analyses at the Palenque site museum. The goal of the paper was the characterization (performed with a multidisciplinary approach) of the green objects belonging to the Palenque Mayan royal burial. PXRF was helpful in tracking the origin of the minerals constituting the analyzed samples, by taking into consideration their elemental compositions, calculated from semiquantitative analyses. In fact, on the basis of the samples' chemical traces ratios, compared with references materials analyzed in the same conditions, two different sources can be identified for the samples' origin: Montagua and Verapaz. Unfortunately, a set of standards of referent materials/stones are not always available. [PERSON] [90] reported the study of several neolithic nephrite axes, discovered in Dhofar governorate (Sultanate of Oman), where the elemental characterization was performed by ED-XRF. In this second case, the data obtained for the samples have been compared by a semi-quantitative method, with the data obtained in one sample collected from the nephrite veins of Lawdar District (Yemen). Despite reporting a good correlation between the nephrite axes compositions and the reference (not only for the ratios of the main constituting elements, but also concerning zinc and potassium traces, probably correlated to secondary minerals), the relationship between the western Yemen mine and the coastal and interior Dhofar site has been only hypothesized. Anyhow, the data acquired allowed the foundations to be laid in relation to interpreting the framework of long-distance exchanges in the area, which can be expanded by further studies. Regarding the elemental composition, two other techniques can be considered and combined in a multidisciplinary approach with standard petrographic analyses: SEM-EDS and LA-ICP-MS. With the first one, a deep study of the morphology and textures combined with chemical information at high magnification can be performed. Considering the second technique, a spot quantitative chemical analysis is possible. It is interesting to note that with LA-ICP-MS, not only the heavier but also the lighter elements can be detected and quantified [20, 81, 82, 167]. Both techniques can supply very important information, complementary to the ones obtained by ED-XRF. The recent (2021) paper of [PERSON] et al.