Cu- and Mn-bearing tourmalines from Brazil and Mozambique were characterised chemically (EMPA and LA-ICP-MS) and by X-ray single-crystal structure refinement. All these samples are rich in Al, Li and F (fluor-elbaite) and contain significant amounts of CuO (up to ~1.8 wt%) and MnO (up to ~3.5 wt%). Structurally investigated samples show a pronounced positive correlation between the <Y-O> distances and the (Li + Mn²⁺ + Cu + Fe²⁺) content (apfu) at this site with R ² = 0.90. An excellent negative correlation exists between the <Y-O> distances and the Al₂O₃ content (R ² = 0.94). The samples at each locality generally show a strong negative correlation between the X-site vacancies and the (MnO + FeO) content. The Mn content in these tourmalines depends on the availability of Mn, on the formation temperature, as well as on stereochemical constraints. Because of a very weak correlation between MnO and CuO we believe that the Cu content in tourmaline is essentially dependent on the availability of Cu and on stereochemical constraints.

Synthetic Al- and B-rich tourmaline crystals described by London (2011) were characterized further by SIMS and new EMP analyses. These tourmalines are the first synthetic B-rich olenites characterized by single-crystal X-ray diffraction, because they are significantly larger than synthetic samples produced in the past. The average final formulas are ^X(Na_0.7□_0.3)^Y(Al_2.5Li_0.4Fe²⁺_0.1)^ZAl₆(BO₃)₃[Si_5.2B_0.5Al_0.3O₁₈]^V[(OH)_2.9O_0.1]^W[O_0.9(OH)_0.1], with a = 15.765(1), c = 7.083(1) Å, ^X(Na_0.7□ _0.3) ^Y(Al_2.5Li_0.5)^ZAl₆(BO₃)₃[Si_4.8B_0.9Al_0.3O₁₈]^V(OH)₃^W[(OH)_0.5O_0.5], with a = 15.746(1), c = 7.075(1) Å, and ^X(Na_0.6Ca_0.1□_0.3)^Y(Al_2.3Li_0.5Fe_0.2)^ZAl₆(BO₃)₃[Si_4.7B_1.2Al_0.2O₁₈]^V(OH)₃^W[(OH)_0.9O_0.1], with a = 15.723(1), c = 7.068(1) Å. The small distances, down to 1.599 Å, reflect relatively high amounts of ^[4]B (up to ~1.2 apfu; refinements with R = ~2%). All these samples also contain significant amounts of ^[4]Al (~0.2 apfu). A pronounced negative correlation (r² = 1.00; only three data points) between temperature during crystal growth (at a constant pressure) and ^[4]B (from refinement) in these synthetic olenites was found.

Copper- and Mn-bearing elbaitic tourmaline (“Paraíba tourmaline”) sometimes contains significant amounts of Pb and Bi. Their position in the tourmaline crystal structure was studied with correlation analysis and bond valence calculations. Correlations between the F content and the X-site charge allow predicting the X-site occupancy. Three sets of tourmaline analyses were studied: (1) Pb-rich tourmalines from the Minh Tien pegmatite, Vietnam; (2) Cu-, Pb- and Bi-bearing tourmalines from the Mulungu mine, Brazil; (3) Cu- and Bi-bearing tourmalines from the Alto dos Quintos mine, Brazil. Two correlations were plotted: (1) the charge by considering only Na¹⁺, Ca²⁺ and K¹⁺; (2) the charge by adding Pb²⁺ and Bi³⁺ to the X-site charge. When plotting correlations for the Minh Tien tourmalines, the correlation significantly improves by adding Pb²⁺ to the X site. For the Alto dos Quintos tourmalines, only a slight increase of the correlation coefficient is observed, while such a correlation for tourmalines from Mulungu interestingly shows a slight decrease of the correlation coefficient. Bond valence calculations revealed that Bi³⁺ and Pb²⁺ can indeed occupy the X site via BiLi(NaAl)_−1, PbLi(NaCu)₋₁ and possibly PbCu(NaAl)₋₁ substitutions as seen in the investigated tourmaline samples. At the Y site, Pb⁴⁺ can be substituted via PbLi(AlCu)₋₁, and Pb^VO(Al^VOH)₋₁, while Bi⁵⁺ does not have any stable arrangement in Cu-bearing fluor-elbaite. The occurrence of Pb⁴⁺ at the Y site could be one explanation for the results of the correlations of the Mulungu tourmalines. Another explanation could be that during the tourmaline crystallization some additional Bi and Pb came into the pegmatitic system and hence disturbed the correlation between the average X-site charge and the F content. Further plots of such correlations in “Paraíba tourmaline” samples might also help to distinguish between the worldwide localities of these rare and sought-after tourmalines.

The crystal structure of a green, transparent, vanadium-rich muscovite-2M₁ (V₂O₃ = 11.35 wt.%, one of the highest amounts reported to date in muscovite) with the optimized formula (K_0.94Na_0.06)_M2(Al_1.20V³⁺_0.61Mg_0.12Cr³⁺_0.07)_T1(Si_1.54Al_0.46)_T2(Si_1.54Al_0.46)O₁₀(OH)₂ and space group C2/c, a 5.2255(6), b 9.0704(10), c 20.0321(21) Å, β 95.773(2)°, Z = 4 has been refined to R = 6.97% for 1070 unique reflections (MoKα). This muscovite, which occurs in small quartz veins in graphite schist from Weinberg mountain, near the village of Amstall, Lower Austria, is distinctly low in Cr (Cr₂O₃ ∼1.4 wt.%) and Mg (MgO ∼1.1 wt.%); Fe, Mn, and Ti are below detection limit. All octahedral cations occupy the M2 site, and the average octahedral bond (M2–O) distance is 1.953 Å. Structural distortions include α = 8.89° and Δz = 0.193 Å, resulting in an interlayer spacing of 3.35 Å. The optical absorption spectrum of this V-rich muscovite shows absorption features at 427 and 609 nm that define a transmission window centered at 523 nm. These absorption features are consistent with those expected for V³⁺ in mica, but the 609 nm band has a slightly longer wavelength than in low-V micas.