Abstract Study of inclusions in gems from secondary deposits can give valuable clues on the geologic (and sometimes geographic) origin of these displaced materials. For the present study, seven gem quality fancy‐coloured sapphires from Songea, Tanzania, were selected with, rarely observed in these gems, garnet inclusions in order to better understand their formation. Therefore, Raman spectroscopy was used to study garnet, as well as rutile, aluminosilicate and mica inclusions. Garnet composition calculations were made using the MIRAGEM Raman spectra software, which was further improved for the purpose of this study. A couple of garnet inclusions were also analysed by energy dispersive X‐ray spectroscopy (EDS) attached to a scanning electron microscope (SEM). All garnet inclusions presented similar Raman spectra, thus similar chemical composition. Chemical analysis demonstrates that these are pyrope‐rich (>40%) garnets with over 30% of almandine and over 20% grossular without any detectable titanium, chromium and sodium. Calculations made using the updated/improved MIRAGEM software were able to indicate the same composition as compatible with the obtained chemical analyses. Muscovite and sillimanite were also identified using micro‐Raman spectroscopy. This inclusion scene is not similar to those described in fancy‐coloured gem sapphires from other localities. The exact geological formation of these gems is yet not understood but might be eclogite or upper mantle related.
The crystal-chemistry of a near-endmember triplite, a manganese fluoro-phosphate [ideal chemical formula Mn 2 (PO 4 )F; a 12.109(2) Å, b 6.5162(8) Å, c 10.117(1) Å, and b 106.16(2)°; space group I 2/a], from a granitic pegmatite exposed in the Codera Valley (Sondrio Province, Central Alps), has been investigated by means of wavelength dispersive electron-microprobe, infrared and Raman spectroscopies, and X-ray powder and single-crystal diffraction.Single-crystal anisotropic structure refinement gave a final agreement index R 1 = 0.0318 for 76 refined parameters and 1128 unique reflections with F o > 4σ(F o ).The structure refinement of triplite from the Codera Valley confirms the topological features previously described both for a natural sample from Mica Lode (Colorado) and for the synthetic compound Mn 2 (PO 4 )F.The structure consists of isolated PO 4 tetrahedra joined with distorted MO 4 F 2 octahedra.The M(1) and M(2) octahedra share their edges to form chains; the chains of M(1) octahedra are parallel to [010], and those of M(2) are parallel to [100].The analysis of the difference-Fourier maps of the electron density of triplite from the Codera Valley reveals a unique position for F, as reported in the literature for the OH-free synthetic Mn 2 (PO 4 )F.In contrast, two mutually exclusive F sites, with partial site occupancy, were reported in a previous structural study of OH-bearing triplite from Colorado (Mica Lode).
