Abstract. A series of 17 museum tourmaline samples from several pegmatites of Minas Gerais, Brazil, were investigated by several techniques including single-crystal X-ray structure refinements, electron microprobe, and laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS). Chemically, most samples are Na-dominant on the X site and therefore belong to the alkali group. They correspond to fluor-elbaites or elbaites, where similar proportions of Al and Li share the Y positions. Elbaites are located close to the elbaitic end-member, with Fe2+ strongly depleted and the schorlitic component negligible, while fluor-elbaites tend to align along the fluor-elbaite to fluor-schorl solid solution. One sample, with vacancies dominant on the X site, is identified as a rossmanite close to the foitite compositional field. Besides the classical schorlitic substitution, several other mechanisms were observed, evolving towards rossmanite (XNa++0.5YLi+=X□+ 0.5 YAl3+), towards liddicoatite (XNa++0.5YAl3+=XCa2++0.5YLi+), or towards oxy-foitite (0.5 XNa++YFe2++0.5W(OH)-=0.5X□+YAl3++0.5WO2−). Single-crystal data indicate a unit-cell parameters varying between 15.8187(3) and 15.9309(3) Å and c parameters ranging from 7.0924(2) to 7.1279(2) Å. These values are similar to those obtained for Brazilian tourmalines of the elbaite–schorl solid solution. A detailed cation distribution has also been established, indicating that the B site is fully occupied by boron, that the T site is mainly occupied by Si and sometimes by minor amounts of B, and that the Z site is mainly occupied by Al with sometimes minor amounts of Fe3+. The X site contains vacancies, Na, K, and Ca, and the Y site is occupied by Li, Al, and Fe2+ and minor amounts of Mn2+, Ti, Mg, and Zn. In two samples, a significant disorder between Li and Ca on the X and Y sites has been observed. The position of our samples in a diagram correlating the fluorine and the Fe2+ contents of tourmalines indicates that they are below the trend admitted for primary pegmatitic tourmalines. This feature can be explained by their occurrence in miarolitic cavities, where fluid circulations may affect the tourmaline composition. Finally, the trace-element contents, including rare earth elements (REEs), are discussed in detail and appear to be influenced by both the geochemical pegmatitic context and crystal–chemical constraints.

Abstract. Structural refinements of single-crystal X-ray diffraction data collected at room temperature both under ambient and under high pressures up to 10 GPa have been used to characterise the octahedral tilting and site distortions of the orthorhombic Pbnm CaIrO3 perovskite-type phase. The octahedral tilting has been evaluated using both the unit-cell lattice parameters and the displacements of the oxygen and A site from their hypothetical positions in an ideal cubic perovskite structure. The difference between the two types of calculations shows that the assumption of rigid and undistorted octahedra made for determining the tilt angles from the unit-cell parameters is valid only as a first approximation, especially in the case of CaRuO3, CaRhO3 and CaIrO3 perovskites, for which polyhedral distortions are significant. CaIrO3 perovskite appears to have much larger tilting and distortion than other CaO perovskites, likely causing the structure to be stiffer than expected from the general trend of the bulk moduli defined by other CaO perovskites. Moreover, in contrast to other CaO perovskites for which the Ca polyhedron is more compressible than the octahedral site, the compressibility of the IrO6 octahedra is very similar to that of the CaO12 polyhedra, giving rise to an octahedral tilting that is independent of pressure at least up to 10 GPa. This behaviour may help reduce the electronic interactions among oxygens of neighbouring octahedra during compression, given the already large tilts present in the CaIrO3 perovskite structure, and it is likely responsible for the bulk modulus's first pressure derivative being smaller than 4. Larger tilting and distortions are also observed for CaO perovskites that have a Pt-group element occupying the octahedral site. Such perovskites have been found to undergo a phase transformation to an orthorhombic Cmcm post-perovskite phase (CaIrO3-type structure) at pressures below 25 GPa, suggesting that a large octahedral tilting and polyhedral distortion may be a requisite for stabilising the orthorhombic post-perovskite phase of CaO perovskite-type materials.

Abstract. Zircon petrochronology is widely used to quantify the age and duration of magma emplacement and differentiation. However, in highly differentiated magmas, such as those forming rare-metal granites, zircon may form at the magmatic–hydrothermal transition, and its primary crystallisation history, together with its secondary hydrothermal overprint, needs to be resolved and clarified. To resolve zircon formation in such evolved and mineralised granitic systems, we investigated heterogeneous zircons from the Beauvoir rare-metal granite (Massif Central, France). Most of the Beauvoir zircons are characterised by the presence of two distinct domains, designated as Zone 1 and Zone 2. Zone 1 occurs as rounded, Si- and Zr-rich domains, which are embedded in the interconnected Si- and Zr-poor Zone 2 domains that are also extremely P-, U-, F-, Ca-, Fe- and Mn-rich. Both of these zones are strongly damaged (metamict) by radioactive decay, mainly from their high U concentrations. Textures and chemical composition strongly suggest that Zone 1 corresponds to magmatic zircon that has been partly replaced by the Zone 2 material during the magmatic–hydrothermal transition. The crystallisation of Zone 1 zircon is preceded by the crystallisation of U-rich cores (∼6 wt % UO2) containing UO2 (uraninite) micro-inclusions, which are then surrounded by a Zone 1 homogeneous rim. These uraninite micro-inclusions resulted from the uranium migration in the metamict and amorphous precursor zircon. U-Pb dating of single zircon grains using chemical abrasion, isotope dilution thermal ionisation mass spectrometry (CA-ID-TIMS) techniques yielded a well-defined discordia line with an upper intercept at 312±2.9 (7.2) Ma (2σ) and a near-zero-age lower intercept. The discordancy reflects the continuous loss of radiogenic lead from a heavily damaged and aperiodic zircon lattice. On the other hand, ID-TIMS data from magmatic apatite of the Beauvoir granite yielded an age of 313.4±0.2 (1.3) Ma (2σ), so far, the most accurate and precise crystallisation age of the Beauvoir granite. Thus, we emphasise that although the study of zircon from highly differentiated systems provides strong insights into the magmatic–hydrothermal transition of these objects, their metamict nature prevents their use to precisely and accurately date the emplacement of rare-metal granite.

Abstract. The new rare-earth element (REE) bearing epidote-supergroup mineral vielleaureite-(Ce), Mn2+Ce(MgAlMn2+)(Si2O7)(SiO4)F(OH), is described from a Paleozoic stratiform Mn ore deposit at the Coustou mine above the village of Vielle-Aure, Hautes Pyrénées, France. It occurs as isolated submillimetric prisms in veinlets crosscutting the microcrystalline rhodochrosite ore, associated with rhodochrosite, friedelite, spessartine, “Mn-humite”, baryte, and numerous sulfides. The dark-brown “allanite”-looking prisms are patchily zoned from vanadoandrosite-(Ce) or vanadoakasakaite-(Ce) to a near-endmember vielleaureite-(REE) composition, with a strict correlation between F and Mg contents. The empirical formula of the crystal studied is, on an eight-cation basis, A1(Mn0.852+Ca0.14Na0.01)Σ1.00 A2(Ce0.66La0.32Nd0.02Er0.01)Σ1.00 M1(Mg0.71V0.14Mn0.082+Mn0.023+Fe0.063+)Σ1.01M2Al1.00 M3(Mn0.982+Mg0.02)Σ1.00 T(Si2.94Al0.04B0.01)Σ2.99O11(F0.85Cl0.01O0.14)Σ1.00 (OH). The mean refractive index calculated for the holotype composition is n=1.79. The calculated density is 4.33 g cm−3. Pleochroism is strong: very light yellow < light brown < brown //b. Monoclinic unit-cell parameters refined from single-crystal X-ray diffraction data are a=8.8238(13) Å, b=5.7131(9) Å, c=10.0034(16) Å, β=112.823(6)°, V=464.80(13) Å3, Z=2. The anisotropic model of the P21/m structure converged to 0.0575 for 1565 reflections with Fo>4σ(Fo) and 126 refined parameters; it confirms the Mn2+ dominance at the A1 and M3 sites and the charge compensation of fluorine incorporation at O4 by Mg at M1, pointing to a new member of the dollaseite group, the A1Mn2+ equivalent of khristovite-(Ce). In the same rocks, “hellandite” was discovered as tiny oriented relict inclusions within vielleaureite-(Ce), locally associated with micrometre-size fluorite and “parisite” inclusions and more rarely as ghost crystals in rhodochrosite. With a Mn/(Mn+Ca) ratio in the range 0.49 to 0.61, this hellandite-group phase is the Mn2+ equivalent of hellandite-(Y).

Abstract. Chemical compositions of mineral phases obtained using a common electron probe micro-analyzer are generally used in many fields of geosciences, like the reconstruction of pressure–temperature paths, because their accuracy ensures high-quality data. However, on submicrometric mineral phases, mostly present in low-grade rocks, the chemical analysis can be contaminated by the surrounding. Energy-dispersive X-ray spectroscopy coupled with a transmission electron microscope is demonstrated to be a valid alternative approach to get high-quality data on submicrometric phases. In this work, we use this approach for geobarometric application on white mica-rich low-grade metapelites from the Internal Ligurian Units (Northern Apennines). Our pressure estimates gave satisfactory results supporting previously geobarometric constraints performed on the same rock samples. The innovative methodological procedure used in this work confirms the tectonic scenario proposed for the Internal Ligurian Units.

Abstract. Karlseifertite (IMA 2024-007, International Mineralogical Association), Pb(Ga2Ge)(AsO4)2(OH)6, is a new member of the dussertite group, from Tsumeb, Namibia. It is a secondary oxidation-zone mineral found on fracture surfaces in germanite–chalcocite ore. Karlseifertite occurs in rosettes of thin, yellow, hexagonal plates up to about 0.2 mm in diameter and usually less than 0.01 mm thick. The mineral has a pale-yellow streak, subadamantine lustre, Mohs hardness of ∼ 4, brittle tenacity, irregular fracture, perfect cleavage on {001} and a calculated density of 4.993 g cm−3. Optically, karlseifertite crystals are uniaxial (+), with ω=1.890(5) and ε=1.894(calc) (white light). The empirical formula from electron probe microanalyses is Pb0.992+(Ga1.603+Ge0.684+Fe0.573+Al0.123+)Σ2.97[(As0.765+S0.156+W0.096+)Σ1.00O4]2(OH0.99)6. Karlseifertite is trigonal with space group R3‾m and unit-cell parameters a=7.2814(7), c=17.1077(12) Å, V=785.50(15) Å3 and Z=3. The mineral has an alunite-supergroup structure (R1=0.0591 for 248 reflections with I>2σI).

Abstract. The new mineral bonacinaite (IMA2018-056), Sc(AsO4) ⚫ 2H2O, was found on the dumps of the Varenche Mine (Saint-Barthélemy, Nus, Aosta Valley, Italy), an old manganese mine, where it occurs as a low-temperature hydrothermal mineral associated mainly with quartz, granular braunite, undefined manganese oxides, arseniopleite, manganberzeliite and thortveitite. Bonacinaite forms colourless (with faint to distinct violet tints), pseudohexagonal, thick tabular crystals, up to 0.25 mm in size, sometimes with annular internal zones showing violet tinges, or as small, faintly violet lath-shaped crystals. The crystals are transparent and brittle, with vitreous lustre. The calculated density of an almost pure bonacinaite crystal is 2.82 g cm−3. Optically, bonacinaite is biaxial negative, α=1.598(4), β=1.618(3), and γ=1.638(3) (measured with a Na light source, 589 nm); 2V (measured) is large, and 2V (calculated) = −88.9°. The empirical formula, based on six O atoms per formula unit is (Sc0.90Mn3+0.08Fe3+0.01Pb0.01)Σ1.00[(As0.95P0.06)Σ1.01O4] ⚫ 2H2O. Bonacinaite has monoclinic symmetry, with space group P21/n and unit-cell parameters (single-crystal data / powder diffraction data) a=5.533(1)/5.521(1), b=10.409(2)/10.336(3), c=9.036(2)/9.059(4) Å, β=91.94(3)/91.97(4), V=520.1(2)/516.7(3) Å3 and Z=4. The crystal structure was refined from single-crystal intensity data obtained from a distinctly Al- and P-bearing crystal to R1(F) = 3.7 % for 1178 reflections. Bonacinaite is isotypic with the other members of the metavariscite group: kolbeckite, metavariscite and phosphosiderite.

Abstract. Rotherkopfite, KNa2(Fe2.52+Ti1.54+)Fe2+(Si4O12)2, is a new member of the neptunite group, from Rother Kopf, Roth, near Gerolstein, Eifel volcanic fields, Rhineland-Palatinate, Germany. It is found in cavities in a quartz–sanidine xenolith embedded in a vesicular alkaline basalt and is associated with fluorophlogopite and an amphibole supergroup mineral that is zoned from potassic-magnesio-fluoro-arfvedsonite on the exterior to potassic-fluoro-richterite in the core. It is presumed to have formed as the result of contact metasomatism of the xenolith by the alkaline basalt melt. Rotherkopfite occurs as brownish-red equant or tabular crystals, up to about 0.2 mm in maximum dimension. The mineral has a light-orange streak, a vitreous lustre, a Mohs hardness of ∼4.5, a brittle tenacity, a curved fracture and a density of 3.20(2) g cm−3. Optically, rotherkopfite crystals are biaxial (+), with α=1.668(5), β=1.678(5), γ=1.720(5) (white light) and 2V(meas) = 53.2(6)°. The empirical formula from electron microprobe analyses, secondary ion mass spectrometry and structure refinement is (K0.87Na0.20)Σ1.07(Na1.99Ca0.01)Σ2.00M1+M2(Fe1.662+Ti1.48Mg0.79Mn0.02)Σ3.95M3(Fe0.642+Li0.16Ti0.15Al0.01)Σ0.96(Si8.00O24). Rotherkopfite is monoclinic with space group C2/c and unit-cell parameters a=16.4599(17), b=12.5457(6), c=10.0487(7) Å, β=115.669(7)°, V=1870.3(3) Å3 and Z=4. The crystal structure (R1=0.0268 for 1324 reflections with I>2σI) is based on two interwoven three-dimensional frameworks: (1) a silicate framework made up of pyroxene-like chains of corner-sharing SiO4 tetrahedra and (2) an octahedral framework made up of chains of edge-sharing metal–oxygen octahedra. The two interwoven frameworks are bound to one another by corner sharing. K and Na are hosted in channels in the combined framework.

ical Museum of China, No. 16 Yangrou Hutong, Xisi, Beijing 100031, People's Republic of China, catalogue number GMCTM2024001 (holotype), and the

Abstract. The factors affecting the calibration of pressure in the piston–cylinder and other solid-media apparatus are so multifaceted and complex as to challenge existing approaches. Here we demonstrate how MgO–ZnO ceramics may be used in piston–cylinder assemblies to routinely record the pressure–temperature conditions experienced by samples in each run. The miscibility gap between rock-salt- and wurtzite-structured phases in the binary system MgO–ZnO is well suited for this purpose as it is capable of recording pressure and/or temperature in situ with a typical sensitivity to pressure of ± 0.02 GPa (1 standard deviation) if temperature is known, or variations in temperature around a sample of ∼ 10 °C assuming pressure is constant. MgO–ZnO ceramics can simply replace the widely used MgO surrounding samples under most conditions, since they are almost as inert chemically as MgO and have similar mechanical properties. As a demonstration, we apply the method to a redetermination of the quartz–coesite univariant phase transition in the piston–cylinder, using different assembly materials, sizes, and pressure–temperature path protocols. Continuous monitoring of piston travel during the entirety of each run helps reveal the differences in behaviour of the apparatus under these variables. We show that several assumptions about the behaviour of the piston–cylinder apparatus are ill-founded, that there may be a discrepancy of ∼ 10 % in pressure between otherwise identical experiments conducted using slightly different experimental protocols, and that the effects of the various options for assembly materials are complex, depending on the pressure–temperature path of the experiment throughout its duration. We have also used the sensitivity of the miscibility gap to temperature to map the temperature distribution in two dimensions surrounding a platinum capsule in a piston–cylinder experiment. The routine inclusion of the ceramic in piston–cylinder assemblies would provide an archive of actual experimental P–T conditions experienced by samples.