Icosahedrite, ideally Al₆₃Cu₂₄Fe₁₃, is a new mineral from the Khatyrka River, southeastern Chukhotka, Russia. It occurs as dark gray-black anhedral to subhedral grains up to 100 μm across, closely associated with spinel, diopside, forsterite, nepheline, sodalite, corundum, stishovite, khatyrkite, cupalite, and an unnamed phase of composition AlCuFe. Icosahedrite is opaque with a metallic luster, possesses a gray streak, and is brittle with an uneven fracture. The density could not be determined. For quasicrystals, by definition, the structure is not reducible to a single three-dimensional unit cell, so neither cell parameters nor Z can be given. In plane-polarized incident light, icosahedrite exhibits neither bireflectance nor pleochroism. Between crossed polars, it is isotropic. Reflectance percentages (R_min = R_max) for the four standard COM wavelengths are 62.3 (471.1 nm), 60.6 (548.3 nm), 58.1 (586.6 nm), and 56.0 (652.3 nm), respectively. The X-ray powder pattern was indexed on the basis of six integer indices, as conventionally used with quasicrystals, where the lattice parameter (in six-dimensional notation) is measured to be a_6D = 12.64 Å, with probable space group Fm3̅ 5̅. The four strongest X-ray powder-diffraction lines [d in Å (I/I₀) (n₁,n₂,n₃,n₄,n₅,n₆)] are: 2.006 (100) (42̅0 042), 2.108 (90) (422̅ 2̅22), 1.238 (30) (604̅ 064), and 3.41 (25) (311̅ 1̅11). Average results of 34 electron-microprobe analyses gave, on the basis of total atoms = 100, the formula Al_63.11Cu_24.02Fe_12.78Si_0.03Co_0.01Ca_0.01Zn_0.01Cr_0.02Cl_0.01. The simplified formula is Al₆₃Cu₂₄Fe₁₃, which requires the mass fractions Al 43.02, Cu 38.60, Fe 18.38, total 100.00 wt%. The new mineral is named for the icosahedral symmetry of its internal atomic structure, as observed in its diffraction pattern. Both the new mineral and mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification, IMA (2010-042).

Melliniite, ideally (Ni,Fe)₄P, is a new mineral from the Northwest Africa 1054 acapulcoite. It occurs as anhedral to subhedral grains up to 100 μm, associated with kamacite and nickelphosphide. Melliniite is opaque with a metallic luster and possesses a gray streak. It is brittle with an uneven fracture; the Vickers microhardness (VHN₅₀₀) is 447 kg/mm² (range 440–454) (calculated Mohs hardness of 8–8½). The calculated density is 7.88 g/cm³ (on the basis of the empirical formula). In plane-polarized reflected light, melliniite is cream-yellowish. Between crossed polars it is isotropic, with no internal reflections. Reflectance percentages (R) for the four standard COM wavelengths are 60.5 (471.1 nm), 50.4 (548.3 nm), 52.5 (586.6 nm), and 55.9 (652.3 nm), respectively. Electron-microprobe analyses give the chemical formula (Ni_2.30Fe_1.64Co_0.01)_{∑ =3.95}P_1.05 on the basis of total atoms = 5. Melliniite is cubic, space group P2₁3, with a = 6.025(1) Å, V = 218.71(6) ų, and Z = 4. The crystal structure has been solved and refined to R = 2.72% using single-crystal X-ray diffraction data. It shows the AlAu₄-type structure, which is an ordered form of the β-Mn structure. The metal atoms occupying the 12b site (M1) are effectively 14 coordinated whereas the metals at the 4a site (M2) are 12 coordinated by three P atoms and nine metals. The phosphorus atoms (4a site) coordinate 12 metal atoms in a somewhat distorted icosahedral arrangement. This new phosphide is the first phase with such a high coordination-number for phosphorus. The new mineral is named after Marcello Mellini, Professor of Mineralogy, who strongly developed the study of meteorites in Italy. The new mineral and mineral name have been approved by the IMA Commission on New Minerals and Mineral Names (2005–027).

Bridgmanite, MgSiO₃ with perovskite structure, is considered the most abundant mineral on Earth. On the lower mantle, it contains Fe and Al that strongly influence its behavior. Experimentalists have debated whether iron may exist in a mixed valence state, coexistence of Fe²⁺ and Fe³⁺ in bridgmanite, through charge disproportionation. Here, we report the discovery of Fe-rich aluminous bridgmanite coexisting with metallic iron in a shock vein of the Suizhou meteorite. This is the first direct evidence in nature of the Fe disproportionation reaction, which so far has only been observed in some high-pressure experiments. Furthermore, our discovery supports the idea that the disproportionation reaction would have played a key role in redox processes and the evolution of Earth.

Extremely Re-rich molybdenite occurs with pyrite in sodic–calcic, sodic–sericitic and sericitic-altered porphyritic stocks of granodioritic–tonalitic and granitic composition in the Sapes–Kirki–Esymi, Melitena and Maronia areas, northeastern Greece. Molybdenite in the Pagoni Rachi and Sapes deposits is spatially associated with rheniite, as well as with intermediate (Mo,Re)S₂ and (Re,Mo)S₂ phases, with up to 46 wt % Re. Nanodomains and/or microinclusions of rheniite may produce the observed Re enrichment in the intermediate molybdenite–rheniite phases. The extreme Re content in molybdenite and the unique presence of rheniite in porphyry-type mineralization, combined with preliminary geochemical data (Cu/Mo ratio, Au grades) may indicate that these deposits have affinities with Cu–Au deposits, and should be considered potential targets for gold mineralization in the porphyry environment. In the post-subduction tectonic regime of northern Greece, the extreme Re and Te enrichments in the magmatic-hydrothermal systems over a large areal extent are attributed to an anomalous source (e.g., chemical inhomogenities in the mantle-wedge triggered magmatism), although local scale processes cannot be underestimated.

We report the first natural occurrence of the Fe-analogue of akimotoite, ilmenite-structured MgSiO₃, a missing phase among the predicted high-pressure polymorphs of Fe-pyroxene, with the composition (Fe²⁺_0.48Mg_0.37Ca_0.04Na_0.04Mn²⁺_0.03Al_0.03Cr³⁺_0.01)_Σ=1.00Si_1.00O₃. The new mineral was approved by the International Mineralogical Association (IMA 2016-085) and named hemleyite in honour of Russell J. Hemley. It was discovered in an unmelted portion of the heavily shocked L6 Suizhou chondrite closely associated to olivine, clinoenstatite and Fe-bearing pyroxene with a composition nearly identical to that of hemleyite. We also report the first single-crystal X-ray diffraction study of a Si-bearing, ilmenite-structured phase. The fact that hemleyite formed in a meteorite exposed to high pressures (<20 GPa) and temperatures (<2000 °C) during impact-induced shocks indicates that it could play a crucial role at the bottom of the Earth’s mantle transition zone and within the uppermost lower mantle.

A dense magnesium iron silicate polymorph with a structure intermediate between olivine, ringwoodite, and wadsleyite was theoretically predicted about four decades ago. As this group of minerals constitute the major component of shocked meteorites, constraining their transitional forms and behaviour is of potential importance for understanding impact events on their parent bodies. Here we use high-resolution transmission electron microscopy techniques and single-crystal X-ray diffraction analyses to identify naturally occurring examples of this mineral – recently named poirierite – in shocked chondritic meteorites. We observe nanoscale lamellar poirierite topotactically intergrown within wadsleyite, and additionally within ringwoodite as recently reported. Our results confirm the intermediate structure of poirierite and suggest it might be a relay point in the shear transformations between its polymorphs. We propose that poirierite formed during rapid decompression at relatively low temperature in retrograde shock metamorphism of the meteorites.