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Natural Fe2+-rich princivalleite was thermally treated in the air at 700 °C to study crystal-chemical and color variations due to changes in oxidation states of Fe and Mn and atom ordering. Overall, the experimental data (electron microprobe, structural refinement, Mössbauer, infrared, and optical absorption spectroscopy) show that thermal treatment of princivalleite results in an almost total Fe2+ oxidation to Fe3+ and an oxidation of approximately one-third of Mn2+ to Mn3+ along with a minor degree of disorder of Al–Fe–Mn over the Y and Z sites. This process is accompanied by a significant deprotonation of the sample. The YFe and YMn oxidation from + 2 to + 3 yields in a decrease in a-parameter, whereas the increased content of ZFe3+ results in a minor increase in the c-parameter. Optical absorption spectroscopy shows that the faint blue (azure) color of untreated princivalleite is caused by the presence of Fe2+ and the absence of Ti4+. Thermal treatment in air (700 °C) changed the color to dark brown due to the progressive oxidation of Fe2+ to Fe3+ and Mn2+ to Mn3+, as demonstrated by the evolution of optical absorption bands caused by electron transitions in these 3d-cations. However, the most evident result of the thermal treatment of the Fe-rich princivalleite sample is the simultaneous presence of Fe2+, Fe3+, Mn2+, and Mn3+, with a Fe3+/ΣFe and Mn3+/ΣMn ratio of 0.92 and 0.25, respectively. This observation suggests that the oxidation process during the heating experiments was largely controlled by kinetic factors. [ABSTRACT FROM AUTHOR]

Two tourmaline crystals with a blue growth zone at the analogous pole, respectively from the San Silvestro and the Fucili pegmatites, located in the San Piero in Campo village, Elba Island (Tyrrhenian Sea, Italy), have been described for the first time using compositional and spectroscopic data to define their crystal-chemical aspects and the causes of the colour. Compositional data obtained by electron microprobe analysis indicate that both tourmalines belong to the elbaite–fluor-elbaite series. The upper part of each crystal is characterised by an increased amount of Fe (FeO up to ~1 wt.%) and a Ti content below the detection limit. Optical absorption spectra recorded on the blue zone of both samples show absorption bands caused by spin-allowed d-d transitions in [6]-coordinated Fe2+, and no intervalence charge transfer Fe2+-Ti interactions, indicating that Fe2+ is the only chromophore. Mössbauer analysis of the blue zone of the Fucili sample confirmed the Fe2+ oxidation state, implying that the redox conditions in the crystallisation environment were relatively reducing. The presence of colour changes at the analogous termination during tourmaline crystal growth suggests a change in the composition of the crystallisation environment, probably associated with a partial opening of the system. [ABSTRACT FROM AUTHOR]

Celleriite, □ ( Mn 2 2 + Al) Al 6 ( Si 6 O 18 ) ( BO 3) 3 (OH) 3 (OH) , $\square \,\left(\text{Mn}_{2}^{2+}\text{Al} \right)\text{A}{{\text{l}}_{6}}\left(\text{S}{{\text{i}}_{6}}{{\text{O}}_{18}} \right){{\left(\text{B}{{\text{O}}_{3}} \right)}_{3}}{{(\text{OH})}_{3}}(\text{OH}),$ is a new mineral of the tourmaline supergroup. It was discovered in the Rosina pegmatite, San Piero in Campo, Elba Island, Italy (holotype specimen), and in the Pikárec pegmatite, western Moravia, Czech Republic (co-type specimen). Celleriite in hand specimen is violet to gray-blue (holotype) and dark brownish-green (co-type) with a vitreous luster, conchoidal fracture, and white streak. Celleriite has a Mohs hardness of ~7 and a calculated density of 3.13 and 3.14 g/cm3 for holotype and its co-type, respectively. In plane-polarized light in thin section, celleriite is pleochroic (O = pale violet and E = light gray-blue in holotype; O = pale green and E = colorless in co-type) and uniaxial negative. Celleriite has trigonal symmetry: space group R3m, Z = 3, a = 15.9518(4) and 15.9332(3) Å, c = 7.1579(2) and 7.13086(15) Å, V = 1577.38(9) and 1567.76(6) Å3 for holotype and co-type, respectively (data from single-crystal X‑ray diffraction). The crystal structure of the holotype specimen was refined to R1 = 2.89% using 1696 unique reflections collected with MoKα X‑ray intensity data. Structural, chemical, and spectroscopic analyses resulted in the formulas: x (□ 0.58 Na 0.42 ) ∑ 1.00 Y ( Mn 1.39 2 + Fe 0.16 2 + Mg 0.01 Al 1.14 Fe 0.01 3.0 Li 0.28 T 0.01 ) Σ 3.00 Z Al 6 [ T ( Si 5.99 Al 0.01 ) Σ 6.00 O 18 ] ( BO 3) 3 (OH) 3 w [ (OH) 0.65 F 0.03 O 0.32 ] Σ 1.00 (for holotype) $\begin{align}& \,\,\,\,{{\,}^{\text{x}}}{{\left({{\square }_{0.58}}\text{N}{{\text{a}}_{0.42}} \right)}_{\sum 1.00}}\text{Y}{{\left(\text{Mn}_{1.39}^{2+}\text{Fe}_{0.16}^{2+}\text{M}{{\text{g}}_{0.01}}\text{A}{{\text{l}}_{1.14}}\text{Fe}_{0.01}^{3.0}\text{L}{{\text{i}}_{0.28}}~{{\text{T}}_{0.01}} \right)}_{\Sigma 3.00}}^{\text{Z}}\text{A}{{\text{l}}_{6}}\left[ {{~}^{\text{T}}}{{\left(\text{S}{{\text{i}}_{5.99}}\text{A}{{\text{l}}_{0.01}} \right)}_{\Sigma 6.00}}{{\text{O}}_{18}} \right]{{\left(\text{B}{{\text{O}}_{3}} \right)}_{3}}{{(\text{OH})}_{3}} \\ & ^{\text{w}}{{\left[ {{(\text{OH})}_{0.65}}~{{\text{F}}_{0.03}}{{\text{O}}_{0.32}} \right]}_{\Sigma 1.00}}\,\text{(for}\,\text{holotype)} \\ \end{align}$ and X (□ 0.51 Na 0.49 ) Σ 1.00 Y ( Mn 0.90 2 + Fe 050 2 + Al 1.36 Fe 004 3 + Li 0.17 Zn 0.04 ) Σ 3.00 Z Al 6 [ T ( Si 5.75 B 0.25 ) Σ 6.00 O 18 ] ( BO 3) 3 (OH) 3 w [ (OH) 0.35 F 0.17 O 0.48 ] ∑ 1.00 (for co-type) $\begin{align}& \,\,\,\,\,{{\,}^{\text{X}}}{{\left({{\square }_{0.51}}\text{N}{{\text{a}}_{0.49}} \right)}_{\Sigma 1.00}}^{\text{Y}}{{\left(\text{Mn}_{0.90}^{2+}\text{Fe}_{050}^{2+}\text{A}{{\text{l}}_{1.36}}\text{Fe}_{004}^{3+}\text{L}{{\text{i}}_{0.17}}\text{Z}{{\text{n}}_{0.04}} \right)}_{\Sigma 3.00}}^{\text{Z}}\text{A}{{\text{l}}_{6}}\left[ ^{\text{T}}{{\left(\text{S}{{\text{i}}_{5.75}}~{{\text{B}}_{0.25}} \right)}_{\Sigma 6.00}}{{\text{O}}_{18}} \right]{{\left(\text{B}{{\text{O}}_{3}} \right)}_{3}}{{(\text{OH})}_{3}} \\ & ^{\text{w}}{{\left[ {{(\text{OH})}_{0.35}}~{{\text{F}}_{0.17}}{{\text{O}}_{0.48}} \right]}_{\sum 1.00}}\text{(for}\,\text{co-type)} \\ \end{align}$ Celleriite is a hydroxy species belonging to the X-site vacant group of the tourmaline supergroup. The new mineral was approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association, proposal no. 2019-089. In the Rosina pegmatite, celleriite formed an overgrowth at the analogous pole of elbaite–fluorelbaite–rossmanite crystals during the latest stage of evolution of pegmatite cavities after an event of a pocket rupture. In the Pikárec pegmatite, celleriite occurs as an intermediate growth sector of elbaite, princivalleite, and fluor-elbaite. [ABSTRACT FROM AUTHOR]