## 4 The Example of the Green Stones
### The Raman Investigation  
Among other vibrational spectroscopic techniques, Raman spectroscopy is considered a powerful tool for identifying minerals and gemstones [66; 118; 119; 120] (see Section 3.3). Because of its peculiarity, it represents a very suitable technique to solve the Green Stones identification problems [96; 121]. Table 4 lists the main Raman features for quick identification of the Green Stones. In fact, considering only the main vibrations, the greater part of the phases constituting Green Stones can be easily distinguished. The problem in the phase identification may occur only when the phases are characterised by the main vibrational modes within 2 cm\({}^{-1}\) Raman shift: jadeite-pumpellite (discussed later in this section), nephrite vs. its pure end members, and the serpentine polymorphs. In fact, \(\pm 2\) cm\({}^{-1}\) is the tolerance commonly accepted for Raman spectrum interpretation, especially when the analysis is carried out on a natural phase [120; 121]. Regarding the nephrite, although actinolite is well recognisable, tremolite pure end member can hardly be detected. To overcome this issue, a deep morphological observation is mandatory. Indeed, as already described (see Section 4.1 and Figure 2c), nephrite must show its characteristic texture, while column-like and/or needle-like _habitus_, with isoriented crystals, are typical of actinolite and tremolite pure terms. Regarding serpentines for gemstone species identification, both of the massive polymorphs, antigorite and lizardite, are accepted and both can be easily distinguished on the basis of their Raman features; nevertheless, the references report spectra more consistent with the first one [122]. On the other hand, chrysotile polymorph shows the main Raman bands strictly near to the lizardite ones. In this case, similar to the nephrite, morphological observation and OM analysis are very helpful because, as already reported, crysotile is the fibrous polymorph of the serpentine species. Similar to Table 4, the same can be observed by the reference spectra reported in Figure 5, where all six spectra reported show relatively strong, sharp, and well-defined bands, as a consequence of the high crystallinity of the materials analyzed. Only the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Mineral** & \multicolumn{3}{c}{**Main Vibrations–Raman Shift (cm\({}^{-1}\))**} & **References** \\
**Phase/Variety** & & & & [96; 120; 123] \\ \hline
**Jadeite** & 1039, 990 & 700 & & [90; 120; 122] \\
**Nepbrite** & 1060, 1032 & 674 & & [90; 124] \\
**(Actinolite)** & 1062, 1027 & 669 & & [90; 121] \\
**(Tremolite)** & 1062, 1031 & 676 & & [90; 121] \\
**S serpentine** & 1044 & 683, 635 & 378 & [122] \\
**(Antigorite)** & 1044 & 683, 635 & 375 & [122; 125] \\
**(Lizarite)** & 1096 b & 690 & & 388 & [125] \\
**(Chrysotile)** & 1105 & 692 & & 389 & [125] \\  & & & & [120; 122; 123] \\  & & & (551\(-\)) 556, & & \\
**Kosmochor** \({}^{1}\) & 950 & 683 & 522, & 340 & [96; 126; 127] \\  & & & 413 (\(-\)418) & & \\
**Chromite** \({}^{1}\) & & 690 b & 560 b & & [126; 128] \\
**Eckermannite** \({}^{1}\) & 1025, 992 & 690 & & [129] \\
**Natrolite** \({}^{1}\) & & & 535, 443 & & [130] \\
**Hydrogrossular** & 871 & & & 361 & [131] \\
**Vesuarite** & 930, 862 & 643 & & [132] \\
**Diopside** & 1010 & 666 & & & [120; 133] \\
**Omphacite** & 1024 & 685 & & [92; 122; 134] \\
**Pumpellite** & 990, 920 & 697 & & [135] \\
**Chalcedony** & & & 503, 465 & & [34; 136; 137] \\ \hline \hline \end{tabular} \({}^{\dagger}\) Main phases constituting Mau-Sit-Sit variety. b = Broad band.  
\end{table} 
Table 4: Raman main features characterizing Green Stones. The main bands of pure actinolite, tremolite phases, together with those of nephrite, and antigorite, lizardite, chrysotile phases, together with those of serpentine, have been reported as references for completeness. omphacite phase shows Raman bands with characteristic Full Width at Half Maximum (FWHM) of the band amplitude higher than other phases (Figure 5), as diopside or jadeite.