The abundance and distribution of rare-earth elements (REE) within fish debris from the Japanese Exclusive Economic Zone around Minami-Torishima Island have been investigated to determine the host materials of REE in the REE-rich deep-sea mud. The study was performed using REE-extraction experiments, field emission electron probe microanalysis (FE-EPMA), transmission electron microscopy with an energy-dispersive X-ray spectrometer (TEM-EDX), laser-induced breakdown spectroscopy (LIBS), Fourier-transform infrared (FTIR) spectroscopy and X-ray absorption near edge structure (XANES) analysis.

The EPMA data indicate that the amount of REE in the apatite in the teeth is less than that in the bone debris. According to TEM-EDX analysis, yttrium (Y) is contained in the rod-like apatite crystals in the bone debris, but not in the long rod-like apatite crystals of the teeth. Analyses by LIBS and EPMA indicate that Y-rich bone debris is also rich in C. The FTIR spectroscopic analysis indicates the presence of carbonate groups within the Y-rich apatite structure. Moreover, the results of the XANES analysis and REE-extraction experiments indicate that Y occurs within the crystal structure of C-bearing apatite in the bone debris. These results suggest that the REE within C-bearing apatite in the fish debris from the Minami-Torishima REE-rich deep-sea mud substitute for Ca in apatite via an ionic exchange reaction, probably Ca2⁺ + P⁵⁺ ↔ REE3⁺ + C⁴⁺.

Terrestrial vascular plants affect Earth’s long-term geological processes, contributing to carbon cycling, chemical weathering and soil formation. Plants transport elements from the soil to their above-ground structures, accumulating a range of macroelements including Na, K, Mg, Ca, Si, S, P and Cl. Wildfire combustion concentrates these macroelements into inorganic ash. This ash is dominated by oxides, carbonates, halides, sulfates and phosphates of Na, K, Mg and Ca. This work describes K₂Ca₂(CO₃)₃, which occurs abundantly in the ash of the desert spoon (Dasylirion wheeleri), a plant native to the Sonoran Desert. Electron microprobe analysis, powder X-ray diffraction Rietveld refinement and Raman spectroscopy confirm that this phase matches synthetic rhombohedral (R3) K₂Ca₂(CO₃)₃. This phase forms during the smouldering combustion of D. wheeleri trunks, producing friable, decimetre-sized, porous, ash lumps that pseudomorphically preserve the plant’s fibrous structure. This ash occurs as glassy, sintered, porous aggregates, dominated by K₂Ca₂(CO₃)₃, with sylvite, calcite, fairchildite, arcanite and minor hydroxyapatite and periclase. Several double K–Ca carbonates form under surficial pressures and temperatures below ~800°C, including K₂Ca₂(CO₃)₃, and bütschliite (K₂Ca(CO₃)₂) and its dimorph, fairchildite. The occurrence of rhombohedral K₂Ca₂(CO₃)₃ and fairchildite are consistent with smouldering between 518 and 780°C. Upon exposure to water, K₂Ca₂(CO₃)₃ rapidly decomposes, leaving calcite. The occurrence of K₂Ca₂(CO₃)₃ as a major phase in the plant ash expands our understanding of Earth’s mineral diversity, provides new insights into the widespread geological process of wildfire ash formation and highlights the role that these fires play in forming mineral phases that are rare in other geological settings. Though K₂Ca₂(CO₃)₃ was first identified in Dasylirion wheeleri, this phase probably forms in other fire-adapted plant species. The occurrence of K₂Ca₂(CO₃)₃ in plant ash is an example of an inorganic phase that bridges the gap between biomineralisation and geological mineral formation.

The new mineral argentopearceite (IMA2020-049) was found at the mine dump of the abandoned Lehnschafter mine, Mikulov–Hrob district (holotype), and later at museum samples (cotypes) from the Moldava fluorite deposit, both in the Krušné hory Mountains, Czech Republic. Argentopearceite is associated with proustite in quartz gangue (Mikulov) or acanthite and proustite in fluorite gangue (Moldava). The new mineral occurs as tabular (pseudo)hexagonal crystals up to 0.8 mm (Mikulov) and 3 mm (Moldava), and as groups and aggregates up to 1 cm. Argentopearceite from Mikulov is steel grey to black. Mohs hardness is ca. 3; the calculated density is 6.29 g.cm–3. In reflected light, argentopearceite is grey with a greenish shade. Bireflectance was not observed and pleochroism is very weak. Anisotropy under crossed polars is moderate with weak greenish and green–blue tints. Internal reflections were not observed. Reflectance values of argentopearceite in air (Rmin/Rmax, %) are: 27.3/30.0 at 470 nm, 26.6/29.3 at 546 nm, 26.2/28.8 at 589 nm, and 25.9/28.1 at 650 nm). The empirical formula for argentopearceite, based on electron-microprobe analyses (n = 15), is (Ag15.95Cd0.02)Σ15.97(As1.82Sb0.11)Σ1.93(S11.03Cl0.05Te0.01)Σ11.09. The ideal formula is Ag16As2S11, which requires (in wt.%) Ag 77.45, As 6.72 and S 15.83, total of 100.00. Argentopearceite is trigonal, P321, a = 14.8583(5), c = 12.3038(15) Å, with V = 2352.38(15) Å3 and Z = 4. Its crystal structure was refined by single-crystal X-ray diffraction data to a final R1 = 0.0773 on the basis of 6594 unique reflections with Fo > 3σ(F) and 242 refined parameters. The structure of argentopearceite mostly conforms to the general architecture of the As-dominant members of the pearceite–polybasite family of minerals.

Single-crystal synchrotron X-ray diffraction data were collected up to 10 GPa at room temperature on a natural omphacite with composition close to Jd43Di57, at the Xpress beamline at Elettra Synchrotron, using a diamond anvil cell. A second-order Birch-Murnaghan equation of state (EoS) fit to the unit-cell volumes determined at 20 pressure points yielded V0 = 422.85(15) Å3, and K0 = 121.3(1.2) GPa. These elastic parameters are consistent with the general trend of the diopside–jadeite join. The structural evolution with pressure was determined from both ab initio simulations and structure refinements to the X-ray intensity data. The consistency between experimental findings and local geometrical distortions identified through ab initio calculations is discussed. A distortion variation at the M1 polyhedron occurs at ∼3 GPa, which correlates with the TILT angle of the T2 tetrahedron which stabilises at a similar pressure, coinciding with a decrease in the rate of M1 deformation under pressure.

These results revealing the structural evolution with pressure correlate with changes observed previously in some Raman shifts in the same pressure range in the same material.

I consider the conditions for defining a mineral by its dominant end-member formula. One can calculate the end-member proportions of the end-members of a mineral provided that the end-members are linearly independent (i.e. they are phase components of the mineral); the result includes the dominant end-member of the mineral. If the end-members used in this calculation are not linearly independent, the corresponding set of simultaneous equations is indeterminate. One may remove an end-member from the system, removing the linear dependence; however, any end-member formula may be removed, leaving various sets of end-members that function as phase components. Each set of end-members produces a different solution for the end-member proportions. Each set of positive end-member proportions may (or may not) result in a different dominant end-member; however, within the compositional limits of the species, the same end-member is dominant over all others calculated with different combinations of component end-members. Problems previously encountered in attempting to calculate the dominant end-member formula were due to (1) using mineral formulae that do not accord with the requirements of stoichiometry, and (2) using end-members that are not components of the system. Where the set of end-members chosen to relate mineral composition to end-member proportions contains an end-member that is a linear combination of the other end-members, one must calculate the end-member proportions for all distinct subsets of linearly independent end-members. The dominant end-member over all sets of end-member proportions with all proportions positive is the dominant end-member. Thus for any mineral formula, the dominant end-member formula may be identified and serves to uniquely characterize and identify the mineral. The arguments used here are illustrated by reference to the minerals of the garnet supergroup.

The new mineral wiperamingaite, NaCaFe3+Al(PO4)F5(OH)·H2O, was found at the Wiperaminga Hill West Quarry, Boolcoomatta Reserve, Olary Province, South Australia, Australia where it has formed by hydrothermal alteration of triplite–zwieselite. Wiperamingaite occurs in a matrix of quartz, minor triplite and pyrite in association with fluorite, bermanite, leucophosphite and phosphosiderite. Crystals are transparent to translucent, brownish-orange to brownish-pink tablets, up to 0.25 mm across. The mineral has a white streak and vitreous lustre. It is brittle with a splintery fracture. The calculated density is 3.11 g/cm3. Optically, the mineral is biaxial (–) with α = 1.538(2), β = 1.599(2), γ = 1.614(2) (white light); 2V = 52(2)°; distinct r > v dispersion; orientation: X = a, Y = b, Z = c; pleochroism: X colourless, Y brown yellow, Z yellow; Y > Z > X.

Electron microprobe analysis provided the empirical formula Na0.97Ca1.01Fe3+0.92Al1.11(PO4)0.97F4.85(OH)1.32·0.95H2O. Wiperamingaite is orthorhombic, P212121, a = 5.3537(11), b = 5.5911(11), c = 26.279(5) Å, V = 786.6(3) Å3 and Z = 4. The structure of wiperamingaite contains chains of cis-corner connected Feφ6 octahedra (φ = O, OH and H2O) running parallel to [010] decorated with corner-connected PO4 tetrahedra. Adjacent chains link by corner-connection between the octahedra and tetrahedra to form sheets parallel to the (001) plane. Alφ6 octahedra (φ = O and F) attach to both sides of the sheets via corner-sharing with PO4 tetrahedra. Naφ11 polyhedra share edges and faces to form a layer between the sheets that links to the sheets via Alφ6 octahedra and Caφ8 polyhedra.

Jatobá is a magnetite-hosted Cu-Ni deposit in the Carajás Domain, Brazil. The deposit is located along E–W structures belonging to the Canaã dos Carajás shear zone and hosted within the Neoarchean Grão Pará Group. Micron to nanoscale investigation of magnetite from mafic host lithologies and Cu-Ni-mineralisation facilitate constraints on ore genesis. Two texturally and geochemically distinct types of magnetite are defined: ‘trellis’ (country rocks) and ‘silicate-mottled’ (ore). An overlap between the types is recognised as ilmenite changes from lamellar trellis to blebby and patchy textures in the silicate-mottled magnetite. The blebby type comprises Al-hydroxides (gibbsite) and talc, replacing hercynite and Mg-amphibole, respectively. The mottled magnetite contains Mg-(Fe)- and Ce-bearing calcic amphiboles, both associated with non-classical pyriboles (NCP). Geochemical signatures change from Ti-Cr-Co-Mn in trellis magnetite to a pronounced REE enrichment in the mottled type. Nano-inclusions of allanite occur as epitactic intergrowths with actinolite within magnetite. Amphiboles in the host rocks mirror those found in magnetite, with ferro-tschermakite present in both cases.

Ilmenite-magnetite nano-thermobarometry yields a range of temperature and logfO2 values (temperature from 728°C at logfO2= –12 to 414°C at logfO2= –31) for re-equilibration between magnetite and ilmenite from initial trellis to the trellis + blebby and to patchy ilmenite in the densely mottled magnetite. Ferro-tschermakite geobarometry enables an estimate of 6.4–7.4 kbar, compatible with amphibolite-facies metamorphism at ∼20 km depth. Syn-metamorphic deformation textures include magnetite + apatite as pods, banding and folds, as well as sigmoidal scapolite and pressure shadows surrounding magnetite. Collectively, these data support a genetic model implying deep shear-zone metamorphism at the base of the Canaã dos Carajás strike-slip structure. This area is a reservoir for metal sources as fluids can tap into granitoids and ultramafic lithologies in the basement. The telescoped transition from trellis to silicate-mottled magnetite records fluid fluxes of variable overprinting effects during protracted fluid–rock interaction.

Iron silicides, including hapkeite (Fe2Si), are rare minerals found in both terrestrial and extraterrestrial environments. In this study, we present the discovery of trigonal Fe2Si in glass from the Blackville site, South Carolina, USA, in a discrete, deeply buried layer where it is associated with suessite and other impact-related materials. The site has been previously studied for its rich assemblage of Fe–Si spherules, platinum, iridium and nanodiamonds. Using advanced micro-computed tomography, scanning electron microscopy, electron microprobe analysis, and single-crystal X-ray diffraction, we have characterised the crystal structure of trigonal Fe2Si, identifying it as a distinct phase from the cubic hapkeite. The high concentrations of V, Ti and P in trigonal Fe2Si and its co-occurrence with suessite suggest an impact-related origin or a lightning strike. Anthropogenic processes, although unlikely, cannot yet be completely ruled out. While this compound represents a new polymorph of Fe2Si, we refrain at this time from proposing it as a new mineral species to the International Mineralogical Association (IMA) because of remaining uncertainties about its formation. Further research is needed to determine whether this trigonal Fe2Si was produced by natural processes or by anthropogenesis.

Bornite (Cu5FeS4) and digenite (Cu9–xFexS5; x = 0.4) have closely related cubic structures and are known for their range of superstructures derived from metal vacancies leading to larger unit cells expressed as n × a, where a = ∼5.5 Å and n is an integer. Such polymorphs can form during cooling from higher temperature bornite (Bn)–digenite (Dg) 1a solid solution (ss). The alleged basket-weave textures in natural bornite are investigated using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) imaging and energy-dispersive X-ray spectrometry. These techniques, combined with crystal modelling and STEM simulations, are suitable for depicting changes in phases related to crystal-structural modularity as they collectively better reproduce atomic distributions in real space. Bornite associated with either chalcocite or chalcopyrite from the Olympic Dam Cu-U-Au-Ag deposit, South Australia has non-stoichiometric Cu/Fe ratios and displays nanoscale basket-weave textures between the main components Bn2a and anilite (Cu7S4); Dg1a is preserved throughout, albeit as a minor phase. Anilite is a derivative of digenite, whereby a = b = √2aDg and c = 2aDg. Two intermediate phases, Dg3a and Bn2a4a, are documented and an additional phase, Bn2a6a, is tentatively suggested to occur in Fe-rich nanodomains within Bn2a. Considering the epitaxial relationships between all phases, we infer that basket-weave textures record phase transitions via polymorphic transformations of parent Bn2a and Dg1a during cooling. Observed phase assemblages are thus linked to cooling of Bn–Dgss in the range 70–87 mol.% Bn along a Cu6.18Fe1.26S5 – Cu9.12Fe0.89S5 tie-line defined from measured compositions. We depict three associations: Bn2a + Dg1a, Bn2a4a + Dg3a, and Bn2a4a/Bn2a6a + anilite, formed during cooling. Polymorph associations like these are relevant for enrichment of critical/precious metals in copper ores because Bi, Pb, Ag, Te and, probably also Au, if dissolved in Bn–Dgss, could be incorporated into superstructures during Cu-Fe-sulfide phase transitions.

Pseudosection modelling of a relict garnet-core in Palaeoproterozoic rocks from the Gridino area in the southern Belomorian belt of Karelia reveals peak-pressure eclogite-facies conditions of 610–650°C, 18–20 kbar for two retro-eclogite samples and 610–665°C, 23–26 kbar for a rare Mg-rich biotite-orthopyroxene eclogite, suggesting low initial metamorphic field gradients of 6.6–10°C/km. This confirms an earlier finding in Karelia and, considering other Palaeoproterozoic eclogite occurrences worldwide, that ‘cold’ subduction conditions, characteristic of modern-style subduction, occurred during the Palaeoproterozoic, ∼2 Ga ago, for the first time in Earth history. However, compositions of most other phases in the retro-eclogite were reset by diffusion, deformation and recrystallisation during subsequent pressure release and heating to variable degrees, a reason for earlier overestimations of temperatures. By contrast, peak-pressure conditions for a biotite paragneiss (640–740°C, 15–18 kbar) that occurs close to the biotite-orthopyroxene eclogite locality already show an early resetting of its initial assemblage. High-pressure granulite-facies peak-temperature conditions of the retro-eclogite at 712± 5°C, 9–12 kbar (along a field gradient of 20°C/km) were determined by Zr-in-rutile thermometry and quartz-in-garnet elastic barometry. These conditions were dated by a Rb/Sr mineral isochron for the biotite-orthopyroxene eclogite at 1830±20 Ma for the first time. Using existing ages for the peak-pressure conditions, possible slow overall exhumation rates of <0.9 mm/y between eclogite and the granulite-facies stages could be determined that are compatible with erosion as the main exhumation mechanism. The peak-temperature conditions were possibly established by thermal relaxation during early exhumation. However, a younger Rb/Sr mineral isochron for the biotite paragneiss indicates a characteristic Sr-isotopic disequilibrium distribution caused by diffusion during slow cooling between ∼1800 and 1750 Ma during later exhumation.

Anningite-(Ce) ideally (Ca0.5Ce4+0.5)(VO4), was found within a phosphate coprolite from the sand-dominated sediments of the Gara Samani Formation, Algeria. As a tetragonal anhydrous vanadate, this mineral is classified in the xenotime group. It occurs in rock cavities and forms small (typically up to 100 μm in length) sheaf-like aggregates composed of crystals 30–40 μm in length and ∼7 μm in diameter. Anningite-(Ce) crystals are green with a vitreous lustre. No cleavage is observed and the fracture is uneven or conchoidal. Its empirical formula, calculated on the basis of 4 oxygen atoms, can be written as (Ca0.52Ce4+0.47Y3+0.01)Σ1.00[(VO4)0.88(PO4)0.05(SO4)0.06(SiO4)0.01]Σ1.00. The calculated density is 3.887 g/cm3. Anningite-(Ce) is tetragonal with space group I41/amd and unit-cell parameters a = 7.1500(4) Å, c = 6.3343(7) Å, and V = 323.82(5) Å3. Anningite-(Ce) is isostructural with wakefieldite-(Ce).

Eleven chert samples from various geographical and geological locations and ages were heat treated, with two of the samples also undergoing in situ X-ray diffraction (XRD) during heat treatment. Characterisation was performed using X-ray fluorescence (XRF), XRD and Raman spectroscopy. The results indicated that the presence of moganite in cherts is independent of whether they are quartzitic or cristobalitic/tridymitic. After heating, cherts cannot be differentiated into these two types using XRD, as all the samples might contain quartz, cristobalite and tridymite. Heat treatment induced transformations in both siliceous and non-siliceous phases, forming new crystalline phases. The observed transformations at 1000°C agree with the literature data. The combination of XRD and Raman spectroscopy is crucial for comprehensive chert analysis, with Raman methods detecting lower concentrations and textural variations than XRD. A correlation exists between chert type (quartzitic or cristobalitic/tridymitic), i.e. mineralogy and age, but not between elemental composition and age. In situ XRD during heating shows distinct crystalline transformations. These transformations can affect significantly the properties of the cherts and has implications for conservation and provenance studies of archaeological tools. The analytical tools used to characterise the mineralogy of cherts are a fast and efficient alternative to conventional petrographic microscopy, especially in the case of heat-treated cherts.

The new mineral pendevilleite-(Y) (IMA 2022-054), ideally Mg2Y3Al(UO2)2(CO3)7(OH)6(H2O)16, was found in the famous Kamoto-East open-cut, Lualaba province, Democratic Republic of Congo and named after Jean-Marie Pendeville (1936–2002), a specialist in collecting minerals of Congo. The new mineral occurs as extremely thin blades (up to ∼0.08–0.10 mm in length and only ∼1 μm thick), often forming lichen-like aggregates and crusts. It is associated with kamotoite-(Y), astrocyanite-(Ce) and shabaite-(Nd), uranophane and sklodowskite. Pendevilleite-(Y) crystals are whitish or greyish-white, locally pale-bluish white. The mineral is brittle; has an irregular fracture and a Mohs hardness of ∼2. Cleavage is perfect on {001}. Electron microprobe analyses provided (on the basis of 2 apfu U with CO32–, H2O derived from the structure and OH– to keep the electroneutrality) formula Mg1.78[(Y1.42Gd0.36Dy0.33Nd0.16Er0.14Sm0.13Eu0.12Tb0.05Ho0.04Yb0.04Ce0.03Tm0.03Pr0.01)Σ2.86 Ca0.11Pb0.01]Σ2.98Al0.88(UO2)2(CO3)7(OH)5.02(H2O)16. Pendevilleite-(Y) is triclinic, P$\overline 1 $, a = 11.9130(3) Å, b = 13.5252(11) Å, c = 16.1531(3) Å, α = 107.052(3)°, β = 92.7765(19)°, γ = 109.676(4)° and V = 2311.5(2) Å3 (Z = 2) at 97 K. The crystal structure (dynamical refinement against 3D ED data; R1 = 0.0948 for 1168 [I > 3σ(I)] reflections) possesses a large heteropolyhedral framework based on both a finite [(UO2)(CO3)3]4– cluster (UTC cluster) and a dimeric [(UO2)2(CO3)4(OH)2]6– unit formed due to olation of uranyl polyhedra. There are three M sites in the structure, occupied by Y3+ and Ln3+, with symmetry-related equivalents forming a polyoxometalate cluster of the general composition [(Y,Ln)6(OH)8(H2O)4(CO3)4]2+. Additionally, there is one Al site in the structure (symmetrically related equivalents forming a dimer of composition [Al2O2(OH)8]6–), and two Mg sites in octahedral coordination MgO2(H2O)4. In the sizeable channels of the framework (running parallel to c), there are at least eight independent partially occupied and disordered O sites of the H2O molecules.

Ranunculite is a rare supergene hydrated aluminium uranyl phosphate reliably reported only from the type locality – the Kobokobo pegmatite in the Sud-Kivu province, Democratic Republic of Congo; its structure has remained unknown until now. Based on 3D electron diffraction data, ranunculite is monoclinic, with a C-centred unit cell: a = 11.1812(7) Å, b = 17.9281(5) Å, c = 17.91548(16) Å, β = 98.350(4)°, and V = 3553.2(2) Å3 (Z = 4). The structure (C2/c) was refined kinematically to R1 = 0.4114 for 1697 unique observed reflections. The structure of ranunculite is based upon infinite uranyl-phosphate sheets of novel topology. The two-dimensional representation of the structural unit consists of hexagons (occupied by U6+), pentagons (occupied by U6+), squares (occupied by Al3+) and triangles (occupied by P5+). Those sheets are stacked perpendicular to c; the interplanar distance is ~9.5 Å. They result from the clusters of edge-sharing uranyl hexagonal and pentagonal bipyramids linked by Al-octahedra and PO4 tetrahedra. The decoration of the sheets is unique but somewhat resembles the arrangement (of U-clusters, squares and triangles) observed in bijvoetite and lepersonnite topologies; the ring symbol is 61514232. In the interlayer, there are two Al3+-hosting sites (one [6]- and [5]-coordinated; the pyramidal one is only partially occupied), as well as isolated H2O groups. There is an extensive network of hydrogen bonds; adjacent sheets are either held by hydrogen bonds only or by tetramers of Al-polyhedra when occupied (through shared O19). This arrangement most probably causes a poor crystallinity of ranunculite (which gives rise to stacking faults observed in the powder diffraction data).

Here we present the first single-crystal X-ray diffraction analysis of zolenskyite, a chromium-bearing sulfide mineral (FeCr2S4) and newly identified polymorph of daubréelite, discovered in the Muonionalusta meteorite, a well-characterized IVA iron meteorite. Zolenskyite occurs as rare micron-scale grains associated closely with daubréelite and stishovite, within a troilite matrix. Chemical analysis confirms a pure, homogeneous FeCr2S4 composition. The crystal structure was refined in the monoclinic C2/m space group, revealing a framework of face-sharing octahedra, consistent with a cation-deficient NiAs-type structure, distinct from the spinel-type structure of daubréelite. Zolenskyite forms under high-pressure (>7 GPa) and high-temperature (>1000 K) conditions, probably through solid-state transformation from daubréelite during shock events. The serendipitous recognition of zolenskyite emphasizes the value of careful micron-scale mineralogical investigations in revealing transient or metastable phases that record otherwise inaccessible physicochemical conditions. These findings contribute to understanding the thermal and shock history of meteorite parent bodies and the stability of Fe–Cr sulfides in extraterrestrial environments.

Fanfaniite, Ca4Mn2+Al4(PO4)6(OH)4·12H2O, from the Hühnerkobel pegmatite mine, Bavaria, has been characterised by chemical analyses and synchrotron single-crystal diffraction. The average crystal structure was refined in space group C2/c (cell parameters a = 10.055(2), b = 24.132(5), c = 6.2590(10) Å, β = 91.35(3)°) to compare with reported monoclinic structures of other calcioferrite-group minerals with general formula Ca4AB4(PO4)6(OH)4·12H2O, A = Mn2+, Fe2+, Mg, B = Al, Fe3+. The average structure contains disordered half-occupied A sites and associated coordinated water molecules. The diffraction data for fanfaniite contains weak reflections that violate the c-glide condition, as also reported for montgomeryite, and in addition contains extremely weak, diffuse reflections requiring a doubling of a, as reported for kingsmountite. Structure refinements were conducted for the noncentrosymmetric C2 model used for montgomeryite and for the P$\bar 1$ model used for kingsmountite. The fanfaniite diffraction data is better explained by the triclinic model with doubled a cell parameter, although the extent of ordering of the A-site cations is considerably lower (56%) than reported for kingsmountite (85%). If the C2 model contributes, it can only be at the scale of the unit cell.