The new mineral, babunaite-(Nd) NdAsO4, was discovered in metasomatic rocks of the Mixed Series near the Nežilovo village in Northern Macedonia. These rocks are characterised by an unusual occurrence of Pb-Zn oxide ore mineralisation. This area forms part of the high-grade metamorphic region of the Upper Precambrian Pelagonian massif. Babunaite-(Nd) is an accessory mineral in pink schists, which mainly consists of Mn-bearing muscovite and quartz, with minor braunite. Accessory minerals are hematite, gahnite, almeidaite, långbanite, zircon, piemontite and piemontite-(Pb), nežilovite, Sb-bearing rutile, fluorapatite, As-bearing fluorapatite, gasparite-(La), chernovite-(Y), arsenoflorencite-(La). Babunaite-(Nd) forms single crystals measuring up to 70 μm in size. The transparent crystals exhibit an adamantine lustre and a pale-yellow colour. The microhardness of babunaite-(Nd) is VHN25 = 578(21) kg/mm2, equivalent to a hardness of 5 on the Mohs scale. The mineral is brittle and does not exhibit cleavage. The mean composition of the holotype crystal is as follows: (Nd3+0.39Ca0.14Th0.09Pr3+0.08La0.07Sm3+0.06Y0.06Gd0.05Ce3+0.02Eu3+0.01)Σ0.97(As5+0.95W6+0.05V5+0.01)Σ1.02O4. The calculated density is 5.918 g·cm–3. Babunaite-(Nd), with the general crystal chemical formula ABO4, has a scheelite-type structure and crystallises in the tetragonal I41/a space group: a = 5.1363(2) Å, c = 11.5764(8) Å, V = 305.41(3) Å3 and Z = 4. The main bands at 190, 348, 440 and 833 cm–1 are distinguished in the Raman spectrum of babunaite-(Nd). A synthetic analogue of babunaite-(Nd) is known, which forms under high-pressure and high-temperature conditions of 11 GPa and 1100–1300°C. The genesis of the Mixed Series rocks occurred under metamorphic conditions approaching the parameters of the kyanite–graphite subfacies, at which gasparite-(Nd) with the monazite structure should form. The formation of babunaite-(Nd) is associated with the stabilisation of its structure by a tungsten (W) impurity. It is the first arsenate phase containing rare earth elements (REE) in the scheelite group.

The triphylite–lithiophilite series, Li(Fe2+,Mn2+)PO4, of primary phosphate minerals are notable for their susceptibility to alteration and their extensive range of alteration products. This article considers the principal crystallographic motifs that relate the crystal structures of the alteration minerals and their relationships to the parent structures. For alteration under oxidizing conditions the common structural motif is a laueite-like heteropolyhedral layer comprising 7 Å corner-connected octahedral chains, cross-linked by M2(TO4)2Φ8 cyclic tetramers. With decreasing temperature of hydrothermal alteration, the structures change, from containing two sets of interpenetrating, quasi-orthogonal, laueite-type layers, to containing one orientation of the laueite-type layers, in two-layer-wide slabs. Alteration minerals formed under supergene conditions, such as the laueite-group minerals have single laueite-type layers interconnected via corner-sharing with hydrated octahedrally coordinated divalent cations. Under reducing conditions, the alteration phases are hydrated minerals, which have structures based on strings of edge-sharing octahedra. They have, in common with the oxidized alteration products, the linking of the octahedral chains by cyclic tetramers that polymerize as kröhnkite-related chains. Motifs present in the structures of the alteration phases can also be identified in the parent structures, suggesting that they may be nucleating sites for the formation/growth of the alteration phases.

The Khaderpet carbonatite (15°58′N, 77°33′E) occurs as a small plug-like intrusion (45 m × 60 m) within altered ultramafic volcaniclastic breccia of unknown parentage. Both the carbonatite and its host rock contain crustal xenoliths of granite and quartz monzonite. Although the absence of primary silicate and oxide phases obscures its direct genetic link with the host rocks, the carbonatite preserves clear evidence of magmatic crystallization subsequently overprinted by hydrothermal alteration, crustal assimilation and supergene oxidation. The rock is dominated by calcite, which occurs in three distinct generations. Early Sr-Ba-rich calcite-1 (0.8–2.1 wt.% SrO and 0.4–2.2 wt.% BaO) phenocrysts co-crystallized with rounded fluorite at temperatures above ∼600°C, and are hosted within a Ba-Sr-poor calcite-2 matrix. Mantle-like bulk-rock δ13C values (–4.21 to –4.62 ‰, VPDB), together with (La/Yb)Cn (>1–100) and Y/Ho (24–34) ratios in calcite-1 and calcite-2, support a primary magmatic origin. Evidence for crustal assimilation includes REE-Si enrichment in apatite (up to 1.3 wt.% SiO2) by a britholite-type substitution, increased allanite abundance near xenolith contacts, Si-rich pyrochlore and interstitial quartz. Coarse calcite-3 veins crosscut the calcite-2 matrix and comprise Mn-Fe-Mg-rich bright calcite-3a cores and nearly pure, dark calcite-3b peripheries. Elevated Mn-Fe-Mg contents and high Y/Ho ratios (up to 64) in calcite-3a reflect rapid crystallization during waning hydrothermal stages. High δ18O values (+9.17 to +11.54 ‰ VSMOW) indicate low-temperature H2O-rich, CO2-poor meteoric fluid alteration. Negative Ce anomalies in apatite (Ce/Ce*: 0.8–0.3) and calcite (Ce/Ce*: 0.8–0.4), most pronounced in calcite-3b (Ce/Ce*: 0.2–0.6), together with apatite trace element compositions, indicate supergene alteration. Textural evidence of supergene alteration includes replacement of pyrochlore-1 by pyrochlore-2, pyrochlore-1 and pyrite by goethite, allanite-(La) by ferriallanite-(Ce), and late precipitation of baryte, REE-fluorocarbonates and vanadinite, indicating involvement of F–, SO42–, Pb and V in oxidizing hydrothermal fluids.

Hydrocalumite, a natural Ca-Al Layered Double Hydroxide (LDH), also known as a hydrated calcium aluminate and an aluminate ferrite monosubstituted (AFm) phase in cement chemistry, has been studied by single-crystal and powder X-ray diffraction, electron probe microanalysis and Raman spectroscopy on a sample from Boisséjour, Puy-de-Dôme, Auvergne-Rhône-Alpes, France. The mineral is monoclinic, space group P2/c, a = 10.0234(3), b = 11.5131(3), c = 16.2989(5) Å, β = 104.205(3)°, V = 1823.39(9) Å3 and Z = 4. The crystal structure has been refined to R1 = 0.0505 based on 6296 unique reflections. The empirical chemical formula of the mineral (Ca, Al, Cl according to electron probe microanalysis; CO2, OH and H2O on the basis of crystal-structure refinement and Raman spectroscopy) is Ca3.96Al2.04(OH)12.04Cl0.96(CO3)0.5˙5H2O that can be idealized as Ca4Al2(OH)12Cl(CO3)0.5·5H2O. The presence of (CO3)2– and (OH)– anionic groups and (H2O)0 molecules is confirmed by Raman spectroscopy. The strongest reflections in the powder X-ray diffraction pattern are (d in Å, Irel in %): 7.89, 100; 3.951, 34; 3.860, 59; 3.753, 26; 2.884, 73; 2.527, 27; 2.501, 38; 2.453, 64; 2.433, 30; 2.327, 25. The crystal structure study reveals the ordering of interlayer species: Cl– and (CO3)2– anions and H2O molecules, which means that both anions play a species-defining role in contrast to the previous suggestions on mono-anionic end-members (with either Cl or OH or CO3 anions). The ordering of two different anions is usually not observed for other LDHs and appears to be a crystal-chemical feature of the Ca-Al LDH members. This work is dedicated to the 150th anniversary of the Mineralogical Society of the UK and Ireland. Hydrocalumite is a mineral with a 90-year history starting from North Ireland, UK, and is a good example of joint efforts of different mineralogical scientific societies in deciphering scientific puzzles.

Hydrated sodium and magnesium sulfates are fairly common minerals. This study is focused on löweite from the fumaroles of the Tolbachik volcano in Kamchatka. The crystal structure of löweite was refined using single-crystal X-ray diffraction, and the hydrogen atoms were localized for the first time. In situ single-crystal (temperature range –173 to 227°C) and powder (temperature range –173 to 900°C) X-ray studies were performed. Both techniques show that löweite remains stable up to ∼220°C without showing any signs of potential phase transitions. The mineral is also stable under a vacuum of ∼600 Pa. The following transformation sequence for löweite was observed upon heating: löweite → metathénardite + vanthoffite + ‘x-phase’ → metathénardite + periclase.

The thermal expansion of löweite demonstrates two distinct patterns in two temperature ranges. There is virtually no expansion in the structure until –93°C. Following this, the structure rapidly expands, exhibiting a highly anisotropic behaviour. Shear deformations of the soft S–O–Mg and S–O–Na hinges explain the structural flexibility and adaptability of löweite to changes in physicochemical environments.

The new mineral almagreraite (IMA2025-025), Cu2+ZnMn4+3O8, was found on the dump of the República Romana mine, Sierra Almagrera, Cuevas del Almanzora, Almería, Andalusia, Spain, where it occurs as tapering prisms or blades up to ∼0.4 mm in length, commonly forming subparallel to divergent aggregates. It is a secondary mineral associated intimately with well-crystallized blades of malachite on a matrix consisting of well-crystallized goethite and massive friable hematite. Crystals are black and opaque with submetallic lustre. The streak is dark grey with a brownish tint. The tenacity is brittle and the fracture is splintery. There are probably two cleavages (possibly {100} and {010}). The Mohs hardness is ∼5. The calculated density is 5.174 g·cm–3 based upon the empirical formula. In reflected light, the mineral is bluish grey in colour with moderate bireflectance and slightly bluish grey to a lighter bluish grey pleochroism. Electron probe microanalyses provided (Mn4+3.05Cu2+0.93Zn0.91Al0.05)Σ4.94O8. Almagreraite is orthorhombic, Pmn21, a = 5.7298(4), b = 4.9715(4), c = 9.3479(7) Å, V = 266.28(3) Å3 and Z = 2. In the crystal structure (R1 = 0.0297 for 423 I > 2σI reflections), Mn4+O6 octahedra share edges forming an octahedral sheet parallel to {001}. One in every four octahedra in the sheet is vacant, providing the sheet formula [Mn4+3O8]4–. Successive sheets are connected via bonds to Cu2+ and Zn2+ located in a layer between the sheets. The structure is similar to that of minerals of the nolanite supergroup and most notably the kamiokite group. Almagreraite is a member of a family of mixed-metal oxides with the generic formula M2Mn3O8, which are an important subject of study for the development of new materials.

Mineralogical crystallography has evolved from the geometric and observational studies of the eighteenth century to a dynamic, predictive science capable of probing matter at atomic and nano-scales. Contemporary advances, including ultrafast X-ray free-electron lasers, high-pressure diamond anvil cells, cryo- and environmental electron microscopy, and multimodal in situ techniques, now permit real-time observation of mineral transformations under extreme conditions. Coupled with computational modelling and predictive simulations, these methods are transforming crystallography into an integrative, interdisciplinary discipline with applications ranging from Earth and planetary sciences to materials engineering. This essay explores technological innovations and emerging frontiers of mineralogical crystallography, highlighting its enduring role in revealing the hidden architectures of matter and guiding the exploration of both natural and synthetic materials.

The new mineral, zavyalovite, ideally Ag2TeS3, was found at the Boevskoe W-Be deposit, Chelyabinsk Oblast, Southern Urals, Russia. It occurs as very small anhedral grains (typically 5–15 μm, max. up to 30 μm across) or narrow veinlets (up to 100 × 5 μm) within galena or at the contact of galena and sphalerite. Zavyalovite is dark red, opaque with sub-metallic lustre, brittle tenacity and uneven fracture. No cleavage or parting was observed. The Vickers’ micro-indentation hardness (VHN, 10 g load) is 95 kg/mm2 (range 93–98, n = 4), corresponding to a Mohs hardness of 2.5. Dcalc. = 5.33 g/cm3. In reflected light of the ore microscope, zavyalovite is grey, very weakly bireflectant and non-pleochroic. Under crossed polarizers the new mineral exhibits strong anisotropy, in grey tones. Internal reflections are abundant, red in colour. The reflectance values for wavelengths recommended by the Commission on Ore Mineralogy of the International Mineralogical Association are (Rmin/Rmax, %): 32.2/31.8 (470 nm), 29.6/29.1 (546 nm), 28.4/27.5 (589 nm) and 27.3/26.5 (650 nm). The Raman spectrum shows bands corresponding to stretching and deformation vibrations in the TeS3 polyhedra. The chemical composition (wt.%, electron microprobe data, mean of eight spot analyses) is Ag 49.31, Te 29.04, S 21.75, total 100.10. The empirical formula calculated on the basis of six atoms per formula unit is Ag2.01Te1.00S2.99. Zavyalovite is monoclinic, space group Cc, with a = 6.8440(8), b = 11.515(1), c = 7.6529(7) Å, β = 114.47(1)°, V = 548.96(7) Å3 and Z = 4. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 3.495 (73) (0 0 2), 3.242 (61) ($\bar 1$ 3 1), 3.017 (57) ($\bar 2$ 0 2), 2.749 (100) (1 3 1), 2.163 (22) (1 3 2), 2.131 (64) ($\bar 1$ 3 3), 1.941 (21) ($\bar 3$ 3 1). The crystal structure of zavyalovite is isotypic with synthetic Ag2TeS3. The new mineral honours Russian mineralogist, crystallographer and expert in sulfotellurides Dr Evgeniy N. Zavyalov (born 1944).