The technique, often abbreviated MDS, exploits a phenomenon sometimes called magneto-Archimedes separation. A non-uniform magnetic field acting on a liquid containing suspended magnetic nanoparticles creates a spatially varying effective density, so that a particle of a given density experiences an apparent buoyancy that pushes it toward the region where the liquid’s effective density equals its own. In the inclined-magnet configuration studied here, those density-matching regions correspond to different horizontal positions along the bottom of a tank. Particles of different densities therefore migrate to different collection zones, where splitters can divide them into distinct products. Because the method works on millimetre-sized particles, it could reject low-value material before energy-hungry fine grinding, a step that dominates the energy budget of many mineral and recycling flowsheets.

The two variables an operator can control are the magnetization of the magnetic liquid and the inclination angle of the magnet. Magnetization sets the range of effective densities the liquid can span, while the inclination angle changes how that density field intersects the tank and the collection system. The catch, identified by the team led by Hongli Su and Francesco Di Maio of Delft University of Technology, is that these variables act together. Some combinations push a predicted cut point outside the usable tank region entirely; others squeeze the width available for collecting the middle product below what the particle size and splitter geometry physically allow. Cranking the magnetization up or tilting the magnet further does not necessarily improve anything, because feasibility depends on the coupled effect of both settings on where the cut points land and how far apart they sit.

To map this behavior, the researchers built a quasi-static density-matching model calibrated against measured densities of the magnetic liquid. The liquid’s baseline density was measured at five magnetization values ranging from zero to 12,000 amperes per metre, yielding densities from 1,000 to 1,250 kilograms per cubic metre, and piecewise-linear interpolation filled in the gaps. An exponential expression for the magnetic field decay then converted each pair of angle and magnetization values into three predicted positions along the tank bottom: the high/middle cut, a representative middle position, and the middle/low cut. A condition was declared feasible only when all matching positions existed within the tank and the magnetic field’s coverage, retained the correct ordering, lay downstream of the feed zone, and left a middle-product window at least as wide as the largest particle plus the splitter thickness, a minimum of 4.5 millimetres for the 2 to 4 millimetre feed used in the study.

The resulting operating map, computed on a fine grid of more than 44,000 parameter combinations, revealed that roughly 81 percent of the explored angle-magnetization space is geometrically feasible, with the maximum predicted middle-product width reaching 14.2 centimetres. The map also exposed the failure modes at the edges of the domain. At a low inclination of 6 degrees with high magnetization, one cut point landed near the edge of the usable magnetic field while the other fell outside it altogether. At the same angle with weak magnetization, the liquid could not reach the effective density needed for the high-density cut at all. These are precisely the kinds of surprises an operator would otherwise discover only by trial and error, and the map makes them visible before any material is fed into the machine.

Sensitivity analyses gave the map a measure of robustness. Perturbing the three target cut densities by one percent changed the predicted collection width at the tested condition by less than 0.55 percent and the feasible-domain fraction by less than 0.19 percent. Refining the numerical grid changed the key metrics by less than a third of a percent, confirming that the 201-by-221 grid was more than adequate. The authors are careful to note the limits of this analysis: the device parameters held fixed in the model, such as the magnetic-field amplitude and magnet geometry, were not varied because experimentally supported uncertainty ranges for them were unavailable, so the sensitivity results apply only to the inputs actually tested.

The crucial test came at a representative operating condition of a 12-degree magnet angle and a magnetization of 5,300 amperes per metre, where the model predicted cut positions at 21.92 and 27.58 centimetres along the tank, leaving a middle-product window of 5.66 centimetres, more than twelve times the required minimum. Splitters were placed at these model-predicted positions, and three independent separation runs were performed on a 2 to 4 millimetre feed of rare-earth-element-bearing material. The high-grade fraction came out at a mean total rare-earth oxide concentration of 5.52 percent by weight, more than double the 2.31 percent in the feed, while the low-grade fraction was depleted to 1.17 percent. The middle fraction sat between at 1.75 percent, exactly the layered partitioning the density-matching picture predicts.

The authors are equally candid about what the experiments do and do not prove. Because the splitter positions were prescribed from the model rather than measured independently from the particle streams, the runs demonstrate density-based product partitioning at one feasible condition; they do not independently validate the predicted positions or the shape of the feasibility boundary across the wider operating space. The opacity of the magnetic liquid also prevented direct tracking of particle trajectories, so transit times and hydrodynamic effects remain unquantified, and the quasi-static model deliberately ignores drag, inertia, and particle-particle interactions. No conditions near the predicted boundary were tested, and energy consumption was not measured, leaving the much-touted grinding-energy savings for future work.

Those caveats point directly to the next steps the researchers consider most important: separation experiments near the predicted feasibility boundary, spatial mapping of the actual magnetic field to check the assumed exponential decay, additional calibration points for the liquid density, controlled measurements of where particles are actually fed, and tracer experiments in an optically accessible system. Each would tighten the assumptions on which the operating map rests and extend its credibility beyond the single tested condition.

The broader significance of the work lies in its reframing of how magnetic density separation should be operated. Rather than chasing a single mathematical optimum or simply maximizing magnetization, the framework identifies the entire region of practically collectable operating conditions, making the constraints explicit and transparent. For engineers, that means splitters can be positioned and operating points chosen with confidence about what the geometry allows, and the same map-based approach could be adapted to other separator configurations. As demand grows for recovering rare-earth elements and other critical metals from waste streams, tools that turn uncertain process tuning into principled operating windows may prove as valuable as the separators themselves.

Subject of Research: Operating-window identification for magnetic density separation of rare-earth-bearing particles

Article Title: Operating-window identification for magnetic density separation

Article References: Su, H., Tang, K., van Beek, M., Rem, P., Bo, Z., Bheemireddy, R., Ali, N., Wu, Y., & Di Maio, F. (2026). Operating-window identification for magnetic density separation. Results in Engineering, 32, Article 113344. https://doi.org/10.1016/j.rineng.2026.113344

Image Credits: AI Generated

DOI: Not provided

Keywords: magnetic density separation, magneto-Archimedes separation, rare-earth elements, recycling, mineral processing, operating window, magnetic liquids, magnet inclination angle, magnetization, density matching, splitter placement, waste sorting

The story of the new mineral begins with a specimen collected on 18 August 2000 by Elsa Pfenninger-Horváth and László Horváth in narrow apophyses — vein-like offshoots three to six centimetres wide — of the Poudrette pegmatite on level 8 of the quarry. The Poudrette pegmatite is the largest pegmatite ever observed at Mont Saint-Hilaire, an agpaitic alkaline igneous complex famed among collectors for producing hundreds of mineral species. Its apophyses radiate outward from the main body for tens of metres, entirely enclosed within an enormous hornfels xenolith, a baked block of country rock. Mineral assemblages shift dramatically across the pegmatite, ranging from silicate-dominated to carbonate-dominated zones, and it was in one of these late-stage carbonate-rich pockets that the thin, bladed crystals of piilonenite-(Nd) formed alongside siderite, calcite, microcline, sphalerite, garronite-Na, quartz, rutile and aegirine.

For years the material hid in plain sight under a placeholder identity. It was thought to be the unknown phase UK119 from Mont Saint-Hilaire, a mystery mineral probed repeatedly without success: Robert Gault analysed it with the electron microprobe in 1999, Joel Grice attempted to solve its crystal structure in 2000, Ralph Rowe collected powder X-ray diffraction data in 2007, and Igor Pekov made further structural attempts between 2009 and 2013. The new examination revealed that UK119 was never a single phase at all. At least two different minerals — piilonenite-(Nd) and an unrelated sodium–cerium carbonate — were mixed together in the same material, having formed at the same time, a coincidence that confounded every earlier attempt. Any information previously attributed to UK119 could therefore refer to either or both of the two phases.

Physically, piilonenite-(Nd) is unassuming. It forms thin, bladed crystals up to 600 micrometres across, colourless to white, with a white streak, vitreous lustre, perfect cleavage on {010} and an uneven fracture. The crystals are so thin and flaky that a Mohs hardness could not be measured, and the mineral shows no fluorescence under ultraviolet light. Its calculated density is 3.21 grams per cubic centimetre. Optically it is biaxial positive, with refractive indices α = 1.546, β = 1.616 and γ = 1.638 and a measured axial angle of 56 degrees. The mineral dissolves slowly in aqueous hydrochloric acid at room temperature with gentle effervescence — the tell-tale fizz of a carbonate releasing carbon dioxide.

Chemical analysis demanded care. Because the mineral is unstable under the electron beam, the team used a JEOL 8230 SuperProbe with a widened 30-micrometre beam to minimise element migration, applying time-dependent intensity corrections for sodium, yttrium and lanthanum. Seven analyses yielded an average composition dominated by neodymium oxide at 23.90 weight percent, with significant cerium, samarium, praseodymium and gadolinium, plus a small yttrium contribution. The empirical formula, calculated on the basis of two cations, is Na1.00(Nd0.48Ce0.17Sm0.13Gd0.07Pr0.06Y0.05La0.02Dy0.02)(CO3)2(H2O)3 — confirming neodymium as the dominant rare earth element. Water and carbon dioxide contents were calculated from stoichiometry because so little material was available for direct measurement. Intriguingly, several areas within the crystals showed extraordinarily high yttrium, up to 18.4 weight percent Y2O3, hinting at a possible yttrium-dominant analogue of piilonenite lurking within the same tiny crystals.

Infrared spectroscopy filled in the structural picture that chemistry alone could not. The Fourier transform infrared spectrum, collected on a microsample pressed in a diamond anvil cell, shows O–H stretching bands between 3105 and 3230 wavenumbers and an H–O–H bending band at 1694 wavenumbers, confirming molecular water, along with C–O stretching vibrations of carbonate groups between 1356 and 1460 wavenumbers. A shoulder at 3420 wavenumbers points to hydroxyl anions, while weak bands at 1061 and 1091 wavenumbers reveal that some carbonate groups are polarised — a mode that would be forbidden in perfectly symmetric, threefold-axis carbonate groups. These spectroscopic fingerprints corroborated the presence of water molecules at three distinct crystallographic sites, later confirmed by bond-valence calculations based on hydrogen-bond distances.

The crystal structure itself proved the hardest prize. Previous structural attempts by Grice and Pekov had failed because the crystals diffract extremely poorly, bent as they are. Laboratory single-crystal diffractometers got the team nowhere, so they turned to synchrotron radiation at the Advanced Light Source in Berkeley, using beamline 12.2.1. Even there the data were poor, with split reflections and streaking across the diffraction pattern. Nevertheless, the team solved the structure in the orthorhombic space group P212121, with unit-cell parameters a = 6.7914 Å, b = 17.135 Å and c = 6.4360 Å, refining against 1364 independent reflections to an R1 of 0.092. The studied crystal proved to be an inversion twin, with domains in a 54:46 ratio. The resulting model matched the powder diffraction pattern well under Rietveld refinement, and the crystallographic data were deposited in the Inorganic Crystal Structure Database.

That structure is genuinely unique in mineralogy. It is layered on (010), built from two alternating types of sheets. One layer consists of vertex-sharing neodymium-centred polyhedra combined with carbonate groups lying flat in the layer. The other contains chains of strongly distorted, vertex-sharing sodium-centred octahedra running parallel to (100), flanked by carbonate groups standing on edge. Water molecules occupy three sites: one connects the sodium polyhedra into chains, while the other two tie the neodymium and sodium layers together through hydrogen bonds. Among the handful of known water-bearing carbonates dominated only by sodium and rare earth elements — thomasclarkite-(Y), shomiokite-(Y), lecoqite-(Y) and adamsite-(Y) — none shares this architecture. Adamsite-(Y) comes closest, with flat-lying and standing carbonate groups, but its layers are configured differently and its sodium layers are joined only by hydrogen bonds.

The deeper significance lies in why neodymium minerals are so scarce. Rare earth elements travel together in nature because of their similar chemistry, which is why the Levinson nomenclature system tags rare earth minerals with their dominant element in parentheses. Cerium, the largest of the light rare earths, boasts more than 160 minerals of its own, and yttrium nearly 140; neodymium, intermediate in size between cerium and yttrium, tends to disperse into both groups rather than concentrate. Only 37 neodymium-dominant minerals appear on the official IMA list as of April 2026, and those described from agpaitic complexes typically formed under highly specific local conditions that separated neodymium from its neighbours. Piilonenite-(Nd) follows a different pattern. Together with the recently described mckelveyite-group minerals bainbridgeite-(NdCe) from Mont Saint-Hilaire and mckelveyite-(Nd) from Russia’s Khibiny Massif, it shows a chemical affinity of neodymium for yttrium rather than cerium. The authors propose that in very late-stage hydrothermal fluids, as yttrium is depleted from solution, neodymium can become the prevalent rare earth element — allowing piilonenite-(Nd) and its kin to crystallise where cerium phases would normally dominate.

The mineral is named in honour of Paula Piilonen, a Canadian mineralogist at the Canadian Museum of Nature, former president of the Mineralogical Association of Canada and senior author of two earlier new-species descriptions from Mont Saint-Hilaire, with the suffix (Nd) following the Levinson convention. The holotype specimen, catalogue number CMNMC 93393, is preserved in the Canadian Museum of Nature collection in Ottawa. For a quarry that has already yielded dozens of first descriptions, piilonenite-(Nd) is a fitting addition — a mineral that spent a quarter of a century mistaken for something else, resisted four separate structural assaults, and finally surrendered its secrets to synchrotron light, revealing a crystal architecture no one had ever seen before.

Subject of Research: Description of the new neodymium-dominant carbonate mineral piilonenite-(Nd) from Mont Saint-Hilaire, Quebec

Article Title: Piilonenite-(Nd), NaNd(CO3)2 ⋅ 3H2O, a new neodymium-dominant carbonate mineral from Mont Saint-Hilaire, Quebec, Canada

Article References: Lykova, I., Rowe, R., Teat, S. J., Poirier, G., & Barnes, S. (2026). Piilonenite-(Nd), NaNd(CO 3 ) 2 ⋅ 3H 2 O, a new neodymium-dominant carbonate mineral from Mont Saint-Hilaire, Quebec, Canada. European Journal of Mineralogy, 38(3), 337-345. https://doi.org/10.5194/ejm-38-337-2026

Image Credits: AI Generated

DOI: 10.5194/ejm-38-337-2026

Keywords: piilonenite-(Nd), neodymium, new mineral species, Mont Saint-Hilaire, carbonate mineral, crystal structure, rare earth elements, agpaitic complex, synchrotron diffraction, Poudrette pegmatite, mineralogy, IMA approval

The new mineral is a neodymium-bearing tungsten oxide hydrate with the ideal formula NdW2O7(OH)(H2O). As its name implies, it is the neodymium analogue of two better-known species, yttrotungstite-(Ce), dominated by cerium, and yttrotungstite-(Y), dominated by yttrium. All three belong to the yttrotungstite group, a small family of rare-earth tungstates that form only under the peculiar chemical conditions created when primary tungsten ores break down in the presence of water and air. The abbreviation assigned to the new species is Ytgs-Nd.

The story of the discovery begins not in the field but in a museum drawer. In 1977, the Luxembourgish geologist Paul Antun collected several samples from Nyakabingo during a field campaign in Rwanda and donated them to the National Museum of Natural History in Luxembourg. Decades later, the museum’s curator Simon Philippo spotted unusual yellow-orange bladed crystals among the material, associated with the tungsten minerals anthoinite and hydrokenoelsmoreite. That chance observation set in motion the full analytical campaign that ultimately confirmed a new species.

Nyakabingo itself is a storied locality. Situated roughly ten kilometres north-northwest of Kigali, it lies within the so-called Tungsten Belt of central Rwanda, part of the Mesoproterozoic Karagwe-Ankole Belt that stretches across Central Africa and is famous for its tungsten- and tin-bearing quartz veins as well as niobium-tantalum-tin pegmatites. The deposit is hosted by an alternating sequence of pyritiferous black shales, quartzites and psammites that experienced low-grade greenschist-facies metamorphism. Argon-argon dating of muscovite from the mineralized veins yielded an age of 992.4 ± 1.5 million years, tying the vein systems to the region’s G4 granites, which are considered the ultimate source of the tungsten.

Two distinct stages of tungsten mineralization shaped the deposit. The first produced scheelite, calcium tungstate, together with massive ferberite, an iron tungstate. The second transformed scheelite into striking pseudomorphs known as reinite, in which ferberite replaces the original mineral while preserving its pseudo-octahedral crystal shape. During a final stage of meteoric alteration, ferberite, feldspar and pyrite were attacked by surface waters, generating clays, iron oxides and a cascade of secondary tungsten phases. It is in these oxidized zones, within samples showing a honeycomb texture, that yttrotungstite-(Nd) crystallized alongside anthoinite and microcrystalline yellowish octahedra of hydrokenoelsmoreite.

In hand specimen terms, the new mineral is easy to miss. It forms transparent, yellow-orange tabular crystals that reach a maximum length of just 100 micrometres, frequently assembled into radiating, starburst-like aggregates. The dominant crystal form is the pinacoid {010}, and the characteristic monoclinic angle of about 105 degrees between the a and c axes is clearly visible on the plates. Twinning parallel to (001) was observed optically, mirroring behaviour documented in yttrotungstite-(Ce). The mineral leaves a white streak, shows a vitreous lustre, does not fluoresce, and is remarkably soft, with a Mohs hardness of only 1, comparable to talc. It is brittle, with one perfect cleavage on (010) and excellent cleavages on (100) and (001).

Because the crystals are so tiny and so scarce, the team could not measure density directly; instead they calculated a value of 6.25 grams per cubic centimetre from the chemical data and the refined unit cell. Optically the mineral is biaxial, with refractive indices of 1.90 and 2.10 measured under sodium light, an optical plane parallel to (010), and pleochroism ranging from light yellow to yellow. The high refractive indices and exceptional density reflect the mineral’s heavy elemental cargo: tungsten is one of the densest elements in the crust, and packing it together with rare-earth cations produces some of the most optically extreme properties seen in hydrous minerals.

The chemistry was pinned down with a Jeol JXA-8200 wavelength-dispersive electron microprobe in Milan, using 17 point analyses at 15 kilovolts with a beam diameter of 3 micrometres. Energy-dispersive measurements confirmed the absence of fluorine. Normalized to 15 positive charges with one hydroxyl group and one water molecule per formula unit, the empirical composition reads (Nd0.36Sm0.13Ce0.12Pr0.08La0.06Gd0.06Y0.05Dy0.03Yb0.02Ca0.01)Σ0.92(W2.02P0.02)Σ2.04O7(OH)(H2O). In other words, the large cation site is a veritable museum of rare-earth elements, with neodymium dominant but samarium, cerium, praseodymium, lanthanum, gadolinium, yttrium, dysprosium and ytterbium all present in measurable amounts, a fingerprint of the complex rare-earth budget of the host rocks.

X-ray diffraction provided the structural proof. Powder data collected in Debye-Scherrer geometry with molybdenum radiation gave unit-cell parameters in excellent agreement with single-crystal results: a = 5.8534(3), b = 8.6881(3), c = 7.0488(4) angstroms, beta = 105.336(5) degrees, and a unit-cell volume of 345.70 cubic angstroms, refined in the monoclinic space group P21/m to a final R1 value of 0.0362. The architecture consists of kinked chains of edge-sharing WO6 octahedra running parallel to the b axis, which the large NdO8 polyhedra stitch together by sharing edges and corners with neighbouring octahedra. Viewed down the b axis, the two kinds of polyhedra occupy alternating planes stacked along the [-101] direction. Neodymium sits in an unusually large eight-coordinated site best described as two tetragonal pyramids sharing a common basal edge, with an average Nd-O bond length of 2.446 angstroms, while the strongly distorted WO6 octahedron mixes three short bonds of 1.764 to 1.881 angstroms with three long bonds reaching 2.204 angstroms.

Bond-valence calculations and Raman spectroscopy sealed the case for the unusual formula. Bond-valence sums matched the ideal values for tungsten, neodymium and the framework oxygens, while the OH5 site summed to 0.84, characteristic of a hydroxyl group, and the OW6 site summed to only 0.33, the signature of a neutral water molecule. Raman spectra recorded at the University of Luxembourg with a 633-nanometre laser showed intense W-O stretching bands between roughly 600 and 1000 wavenumbers, with the strongest peak at 930 wavenumbers assigned to the shortest tungsten-oxygen bonds, and five O-H stretching bands between 3350 and 3600 wavenumbers whose positions match the hydrogen-bond distances measured in the crystal structure. Beyond confirming the new species, the study prompted a nomenclature cleanup: applying the same bond-valence logic to the older species shows that yttrotungstite-(Y) and yttrotungstite-(Ce) also contain one hydroxyl group and one water molecule per formula unit, so their formulas have been revised to YW2O7(OH)(H2O) and CeW2O7(OH)(H2O), unifying the whole group. Holotype material is preserved in the collections of the National Museum of Natural History in Luxembourg, catalogue number WPA504, and at the Laboratory of Mineralogy of the University of Liège, catalogue number ULG 21981, ensuring that this tiny but scientifically rich piece of Rwanda’s geological heritage will remain available to researchers for generations.

Subject of Research: Crystallographic and chemical characterization of the new rare-earth tungstate mineral yttrotungstite-(Nd) from Rwanda

Article Title: Yttrotungstite-(Nd), a new mineral species from the Nyakabingo tungsten mine, Kigali, Rwanda

Article References: Hatert, F., Philippo, S., Vignola, P., & Guennou, M. (2026). Yttrotungstite-(Nd), a new mineral species from the Nyakabingo tungsten mine, Kigali, Rwanda. European Journal of Mineralogy, 38(4), 373-382. https://doi.org/10.5194/ejm-38-373-2026

Image Credits: AI Generated

DOI: 10.5194/ejm-38-373-2026

Keywords: yttrotungstite-(Nd), new mineral species, neodymium, tungsten, Nyakabingo mine, Rwanda, crystal structure, rare-earth elements, secondary mineralization, X-ray diffraction, Raman spectroscopy, IMA approval

The researchers, led by Wenfeng Zhang and corresponding author Pingli Mao, studied a magnesium alloy containing 3 weight percent gadolinium, a rare earth element that is increasingly favored in lightweight structural metals for automotive and aerospace applications. Their method combined an in situ tensile test, in which a sample is stretched inside a microscope while being continuously imaged, with electron backscatter diffraction, a technique that maps the crystallographic orientation of every grain in the material. This pairing allowed them to track individual {10-12} tensile twins as they nucleated, swept across grains, and met one another in real time.

Tensile twins are the workhorses of deformation in hexagonal close packed metals like magnesium. Because the hexagonal lattice cannot accommodate large strains through ordinary dislocation slip alone, twins provide an alternative pathway: the lattice within the twin region rotates by roughly 86 degrees, reorienting part of the crystal so that further deformation becomes easier. Which twin variants appear, and how they interact, feeds directly into the alloy’s yield strength, strain hardening, and ultimate ductility, which is why metallurgists have spent decades trying to predict and control twin behavior.

The first striking result concerns what happens when twins of the same type collide. Within a single grain, when identical twin variants come into contact, the team observed that they merge into a single continuous twin band and continue growing as one. This coalescence is mechanistically sensible: because both regions share the same crystallographic relationship to the parent lattice, there is no mismatch barrier at their meeting point, and the twin boundary simply bridges the gap. The merged twin then behaves as a unified deformation feature, capable of propagating further across the grain.

Different variants tell a very different story. When two distinct twin variants collide within the same grain, their lattices are misoriented relative to each other, and the junction between them cannot simply heal. Instead, the researchers found that the collision site becomes a zone of local stress concentration, and both twins stop growing there. In effect, a different-variant impingement acts as a built-in roadblock, arresting twin propagation and locking stress into a microscopic region of the metal. Such interactions are believed to influence crack initiation under continued loading, making their documentation a meaningful contribution to understanding failure in magnesium alloys.

Twins, however, do not respect grain boundaries any more than they respect each other. The study revealed that complex twin interactions also occur across grain boundaries, producing paired structures the authors call twin pairs, where a twin in one grain has triggered the nucleation of a matching twin in its neighbor. The team found that twin co-nucleation of this kind is favored when both grains offer a high Schmid factor, a classical measure of how favorably a crystal is oriented for slip or twinning under the applied stress, and when the geometry compatibility factor, written as m-prime, is also high. The m-prime factor, introduced by Luster and Morris in the 1990s, quantifies how well the directions of maximum shear in two neighboring grains align across their shared boundary.

One of the most consequential observations is that geometry compatibility can sometimes override the Schmid criterion altogether. The researchers documented cases in which a twin pair formed even though one of the two twins had a Schmid factor far too low for it to nucleate on its own under the global applied stress. The explanation is that the twin with a high Schmid factor, growing toward the boundary in the adjacent grain, transfers enough localized stress across the interface to push the poorly oriented grain over its twinning threshold. When the m-prime value of the pair is sufficiently high, the mechanical compatibility of the two lattices makes this stress transfer efficient enough to activate a variant that classical, orientation-only arguments would rule out.

To capture these global-and-local effects in a single framework, the team applied the composite Schmid factor, an approach that incorporates both the applied stress and the local stress contributions transmitted from neighboring grains. This composite measure, previously used to understand common grain boundary twins in magnesium alloys, proved more accurate than the standard Schmid factor at explaining the formation of twin pairs in which both members would normally fail the orientation test. In other words, a twin’s fate is not decided solely by its own crystallographic orientation, but by the mechanical whispering of the grain next door.

Finally, the researchers performed a statistical analysis of where twin pairs preferentially form, combining two parameters: the grain boundary misorientation angle, which describes how far apart in orientation the two neighboring lattices are, and the geometry compatibility factor m-prime. The outcome was a remarkably clean rule of thumb for the Mg-3Gd alloy. The majority of twin pairs formed at boundaries where the misorientation angle was less than or equal to 38.4 degrees and where m-prime was greater than or equal to 0.7. Low-angle, geometrically compatible boundaries, it turns out, are the fertile ground for cross-boundary twin transmission in this alloy.

The implications stretch well beyond a single alloy composition. Magnesium is the lightest structural metal, roughly 75 percent less dense than steel, and rare earth containing magnesium alloys are prized for their high strength and creep resistance in everything from gearbox housings to aircraft components. Yet magnesium’s limited ductility remains a persistent obstacle, and that limitation is rooted in exactly the kind of twin interactions this study documents. Understanding where twins arrest, where they merge, and where they transmit across grain boundaries gives alloy designers quantitative targets: microstructures engineered to promote compatible, low-angle boundaries could encourage stress transfer and improve ductility, while deliberately placing different-variant impingements could localize stress and potentially be exploited to strengthen the material.

The work also adds to a rapidly growing toolkit for studying twinning in situ. Recent years have seen twin nucleation imaged in three dimensions, traced by digital image correlation, and modeled with crystal plasticity and phase field methods, and gadolinium-bearing alloys in particular have attracted attention for their unusual dislocation behavior. By pairing live tensile observation with orientation mapping and by testing the predictive power of the composite Schmid factor and m-prime statistics in a gadolinium-containing system, the Shenyang team has helped close the gap between what simulations predict about twin pair formation and what actually happens inside a deforming metal. Every merged twin, stalled front, and transmitted nucleus they recorded is a data point in the long effort to turn brittle-feeling magnesium into a forgiving, formable engineering metal, and their boundary-misorientation threshold offers future studies a concrete, testable rule to build on.

Subject of Research: Tensile twin interactions and twin pair formation in a Mg-3Gd magnesium alloy observed by in situ EBSD tensile testing

Article Title: Analysis of {10(\bar{1 })2} tensile twin interaction in Mg–3Gd alloy by in situ tensile observation

Article References: Analysis of {10(\bar{1 })2} tensile twin interaction in Mg–3Gd alloy by in situ tensile observation. (n.d.). https://doi.org/10.1007/s10853-026-13818-1

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13818-1

Keywords: magnesium alloys, deformation twinning, twin interaction, grain boundaries, in situ tensile testing, electron backscatter diffraction, Schmid factor, geometry compatibility factor, Mg-3Gd alloy, rare earth elements, mechanical properties, twin transmission

The material belongs to a class called layered double hydroxides, or LDHs, structures best imagined as positively charged metal hydroxide sheets stacked like a deck of cards, with water and mobile anions filling the spaces between them. That architecture gives LDHs an unusually high density of electroactive sites exposed to the electrolyte, which is exactly what a pseudocapacitive electrode needs, because charge storage in these materials relies on fast, reversible redox reactions occurring at or near the surface. Nickel and cobalt have dominated the field precisely because both metals shuttle readily between oxidation states, but LDHs made from them suffer from well-known weaknesses: sheets that tend to restack and block access to active sites, moderate electrical conductivity, and structural degradation under the mechanical stress of long-term cycling.

The Indian team’s strategy was to attack those weaknesses from two directions at once. First, they chose a hydrothermal synthesis route, sealing metal precursors in an aqueous reaction medium and letting them crystallize under elevated temperature and pressure. Hydrothermal growth is prized in electrode research because it encourages the formation of well-ordered nanosheet architectures rather than tangled or amorphous precipitates. In the resulting material, scanning electron microscopy and transmission electron microscopy revealed a hierarchical nanostructure—a network of sheets arranged across multiple length scales—which the authors attribute to the controlled crystallization that the hydrothermal environment makes possible. Such hierarchical textures matter enormously in practice, since they create channels for ions to penetrate deep into the electrode rather than stalling at its outermost surface.

The second lever was the lanthanum itself. Lanthanum ions, with their large ionic radius and stable trivalent state, act as a structural and electronic modifier when incorporated into the nickel-cobalt hydroxide layers. According to the study, the presence of La3+ produced a slight increase in the interlayer spacing—the gap between the stacked hydroxide sheets—effectively propping the deck of cards open. Wider galleries mean easier access for hydroxide ions from the electrolyte, more intercalation sites during charging and discharging, and reduced sheet-to-sheet restacking that would otherwise render much of the material electrochemically dead. Rare-earth elements have been steadily gaining attention in the electrode literature for exactly this kind of role, with earlier work reporting improved capacity and lifespan when lanthanum or other rare earths were coupled with nickel-cobalt systems, including recent studies on synergistic lanthanum and scandium doping in nickel-cobalt LDHs and on lanthanum-oxide and nickel-cobalt LDH nanocomposites.

Structural confirmation came from X-ray diffraction, which verified the formation of the LDH crystalline phase through its characteristic (003) and (006) reflections—the fingerprint of a well-ordered layered lattice. The doping-related expansion of the interlayer spacing showed up as a small shift in these peaks, tying the atomic-level chemistry directly to the nanostructure. That connection between synthesis, structure, and performance is the intellectual core of the work: the authors argue that the synergistic effects of multi-metal redox properties and the structural adjustments induced by lanthanum incorporation are jointly responsible for the electrode’s behavior, rather than any single ingredient acting alone.

The electrochemical evidence followed a standard but rigorous testing regime. Cyclic voltammetry traced the redox reactions as the applied potential was swept back and forth, mapping how much charge the material could store and how quickly. Galvanostatic charge-discharge cycling measured the practical capacity under constant current, while electrochemical impedance spectroscopy probed the internal resistance and the speed of ion and electron transport within the electrode. Together, the three techniques returned the headline numbers: 390.3 mAh per gram of specific capacity, roughly 85.5 percent capacity retention over extended cycling, and 98.56 percent coulombic efficiency, meaning that almost every electron injected into the electrode during charging is recovered during discharge—a critical figure for real devices, where side reactions silently bleed away stored energy.

Crucially, the researchers did not stop at the half-cell level, which can flatter a material before it meets the demands of a complete device. They assembled an asymmetric supercapacitor, pairing the NiCoLa LDH as the battery-like faradaic electrode with a capacitive counter-electrode, allowing the device to span a wider operating voltage window than either electrode could tolerate alone. The full cell delivered a specific capacity of 34.17 mAh per gram, a specific energy of 17.08 Wh per kilogram, and a specific power of 500 W per kilogram. Those figures sit in a genuinely interesting part of the energy landscape: conventional carbon-based supercapacitors typically offer high power but only a few watt-hours per kilogram, while batteries deliver far more energy but slower charging and shorter cycle lives. An asymmetric device in the double-digit energy range with strong power delivery and rapid charging ability is precisely the hybrid profile that applications from regenerative braking to grid frequency regulation demand.

The broader context makes the result more than a one-off material triumph. The field of nickel-cobalt LDH electrodes has produced a rich catalogue of enhancement strategies in recent years: doping with sulfur, pairing LDHs with MXenes or graphene, growing heterostructures with oxides and sulfides, anchoring nanosheets onto carbon cloth or nickel foam, and assembling trimetallic layered hydroxides with hierarchical micro-flower morphologies. Each approach targets the same set of bottlenecks—conductivity, surface area, structural stability, and rate capability. The new study’s contribution is to show that lanthanum incorporation, delivered through a relatively simple and scalable hydrothermal route, can address several of those bottlenecks simultaneously without the complexity of multi-step heterostructure engineering. The hydrothermal method also avoids the need for binders in some configurations and produces crystalline material in a single vessel, factors that matter when research results must eventually translate into manufacturable electrodes.

There are, of course, the familiar caveats that attend any laboratory-scale energy-storage advance. The reported capacity retention, while respectable at about 85.5 percent, still implies measurable fading over the tested cycling window, and the path from a coin-cell or beaker-scale device to the robust, kilowatt-scale modules that real infrastructure requires involves challenges of electrode loading, electrolyte management, and thermal behavior that laboratory papers rarely address in full. The authors themselves frame the work as establishing the material as an advanced candidate for next-generation supercapacitors—a claim about promise and mechanism rather than a finished commercial technology. Still, the specific numbers reported are competitive within the current literature on LDH-based asymmetric devices, and the mechanistic story—lanthanum widening the interlayer galleries while nickel and cobalt carry the redox load—offers a clear design rule for other researchers to test and refine.

What gives the work its wider significance is the growing recognition that rare-earth chemistry may be one of the more underexploited levers in pseudocapacitor design. Lanthanum’s large size, its reluctance to participate directly in the redox chemistry, and its oxophilic character make it less a charge-storage agent than an architect: it holds the layered house open, stabilizes the lattice against the swelling and shrinking of repeated cycling, and subtly redistributes electronic density across the nickel and cobalt centers that do the electrochemical work. The Madurai team’s demonstration that this architectural role can be delivered through straightforward hydrothermal synthesis—using equipment and processes already common in materials laboratories—suggests that NiCoLa LDH and its cousins could move quickly from journal pages to prototype devices. For a world urgently needing storage that bridges the gap between instantaneous power and long-duration energy, electrodes built from carefully tailored decks of metal hydroxide cards may prove to be one of the quiet, materials-level breakthroughs on which faster progress is built.

Subject of Research: Lanthanum-doped nickel-cobalt layered double hydroxide electrodes synthesized hydrothermally for high-performance supercapacitor energy storage

Article Title: Tailoring NiCoLa layered double hydroxide via hydrothermal synthesis for superior supercapacitor performance

Article References: Prabhu, B., Karthickprabhu, S., Mahendran, M., & Deepikaa, M. (2026). Tailoring NiCoLa layered double hydroxide via hydrothermal synthesis for superior supercapacitor performance. Ionics. https://doi.org/10.1007/s11581-026-07477-0

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07477-0

Keywords: layered double hydroxide, supercapacitor, hydrothermal synthesis, lanthanum doping, nickel-cobalt electrode, pseudocapacitance, energy storage, asymmetric supercapacitor, electrochemistry, rare earth elements, specific capacity, nanosheets

Bainbridgeite-(NdCe) has the ideal chemical formula Na2Ba2NdCe(CO3)6·3H2O, meaning that each unit of the mineral combines two sodium atoms, two barium atoms, one neodymium atom, one cerium atom, six carbonate groups, and three water molecules. It belongs to the mckelveyite group, a family of rare hydrated carbonates whose general formula can be written as A3B3(CO3)6·3H2O, where the A sites are occupied by elements such as sodium, calcium, yttrium, zirconium, and neodymium, while the B sites host strontium, barium, cerium, and lanthanum. The new species is the neodymium analogue of bainbridgeite-(YCe), which was described from the same locality in 2024, and it is also the barium-neodymium analogue of alicewilsonite-(YCe). Both the mineral and its name were approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association under proposal number IMA 2023-018, and the holotype specimen has been deposited in the collection of the Canadian Museum of Nature in Ottawa under catalogue number CMNMC 90534.

The mineral was found at the Poudrette quarry, a site within the Mont Saint-Hilaire alkaline and agpaitic complex that has produced an extraordinary number of new mineral species over the decades. Bainbridgeite-(NdCe) turned up in two quite different geological settings. The first is an environment referred to in the literature as carbonate pegmatites or carbonate vugs, bodies rich in calcite that lack the pyroxene and amphibole minerals typical of alkaline pegmatites and whose origin remains poorly understood. In this setting, the type material was recovered from a heavily altered body consisting mostly of calcite and albite, collected by Elsa Pfenninger-Horváth and László Horváth in February 1978. There, bainbridgeite-(NdCe) forms thin rims, up to twenty to thirty micrometers thick, on barrel-shaped short prismatic crystals reaching two millimeters in size. Remarkably, the cores of those same crystals are composed of bainbridgeite-(YCe), with an intermediate zone corresponding to a member of the bainbridgeite-(YCe)-alicewilsonite-(YCe) series, so a single crystal records a sequence of changing chemical conditions during its growth.

The second occurrence is quite different. In a hornfels rock, bainbridgeite-(NdCe) appears as white or pale-grey tabular, saucer-shaped crystals up to half a millimeter across, commonly stacked together and associated with yellow acicular rutile, colourless hexagonal tabular gmelinite-Na, sphalerite, calcite, analcime, and pyrite. In these crystals, the entire grain is bainbridgeite-(NdCe), with no yttrium-dominant core. The coexistence of the mineral in both a carbonate-rich vug environment and a hornfels highlights the versatility of late-stage fluids in the Mont Saint-Hilaire complex, which apparently could deliver the right combination of sodium, barium, carbonate, and rare-earth elements in more than one geological context.

Physically, bainbridgeite-(NdCe) is a pale yellow, pale orange, white, or pale grey mineral with a white streak and a vitreous lustre. It shows no cleavage, has an uneven fracture, and a Mohs hardness of three, determined on material from the hornfels occurrence because the rims in the holotype are too thin for such a test. The mineral is non-fluorescent under ultraviolet light, and its calculated density is 3.49 grams per cubic centimeter. Optically it is biaxial positive, with refractive indices of 1.577, 1.592, and 1.657 for the three principal axes, and a measured axial angle of forty degrees. These modest, unassuming properties are typical of the mckelveyite group, whose members are usually recognized not by striking appearance but by careful chemical and crystallographic analysis.

Characterizing the new species demanded a battery of analytical techniques, and the researchers had to contend with some serious practical obstacles. Electron microprobe analyses were performed with a JEOL 8230 SuperProbe using wavelength-dispersive spectroscopy, but bainbridgeite-(NdCe) is unstable under the electron beam, so larger beam diameters of ten to twenty micrometers were used to minimize element migration, and time-dependent intensity corrections were applied for several elements. Water and carbon dioxide contents could not be measured directly because of the scarcity of material and were instead calculated from stoichiometry. Infrared spectroscopy, carried out at the Canadian Conservation Institute on a tiny fragment mounted in a diamond anvil cell, confirmed the presence of water molecules through characteristic oxygen-hydrogen stretching and hydrogen-oxygen-hydrogen bending bands, and revealed a band at 1064 wavenumbers indicating that the carbonate groups in the structure are polarized rather than symmetric.

X-ray diffraction work proved equally challenging. Powder diffraction data could not be collected from pure bainbridgeite-(NdCe), because not enough separate grains could be recovered, so the measured pattern represents an average of the new mineral and its yttrium-dominant neighbour. Single-crystal diffraction, performed at the Natural History Museum in Oslo on a Rigaku XtaLAB Synergy-S diffractometer, faced the same problem: because bainbridgeite-(NdCe) occurs only as a thin rim on bainbridgeite-(YCe) and the boundary between the two phases is not visually identifiable, the structural model represents an average of both phases. Even so, the structure was solved and refined to an R1 value of 0.036 in the triclinic space group P1, with unit-cell parameters a of 9.0525 angstroms, b of 9.1178 angstroms, c of 6.8518 angstroms, and a cell volume of 438.23 cubic angstroms. The structure is of the weloganite type and is strongly pseudotrigonal, with six independent large-cation sites forming two alternating layers parallel to the ab plane, three water molecules bonded to barium- and sodium-centred polyhedra, and six carbonate groups, three of which lie nearly coplanar with the (001) plane.

The heart of the discovery lies in the distribution of cations among those sites. By combining electron microprobe data, refined site-scattering factors from the diffraction experiment, interatomic distances, bond valence calculations, and charge balance, the team demonstrated that neodymium atoms overwhelmingly prefer the site designated Nd6, while cerium atoms concentrate at the Ce3 site. The evidence is compelling from chemistry alone: the neodymium content of the holotype, 0.35 atoms per formula unit, is significantly higher than that of any single heavier lanthanide, higher than the combined total of all heavier lanthanides from samarium through dysprosium, higher than the yttrium content, and far higher than the neodymium content of the yttrium-dominant holotype of bainbridgeite-(YCe). A specimen from the hornfels shows an even stronger pattern, with 0.41 atoms of neodymium per formula unit. Structural evidence reinforces the case: the site occupied predominantly by yttrium in bainbridgeite-(YCe) is instead dominated by neodymium and other lanthanides in the new mineral, consistent with a substitution of yttrium by rare-earth elements at that position.

Why does neodymium, an element that usually disperses among other rare-earth-bearing minerals rather than forming its own phases, concentrate here? The authors propose a mechanism rooted in crystal chemistry. Neodymium has a particular affinity for yttrium, and in late-stage agpaitic environments, as yttrium becomes depleted from the residual fluid, neodymium can rise to become the dominant rare-earth element in a newly forming phase. The team previously demonstrated this behaviour in piilonenite-(Nd), another neodymium-dominant carbonate from Mont Saint-Hilaire. The model makes a testable prediction: samarium and gadolinium, which are smaller than neodymium but larger than the heavy rare earths that typically follow yttrium, should show an even greater affinity for yttrium-favouring sites and should therefore also become enriched in late-stage phases. The chemical data bear this out. Samarium and gadolinium contents rise from negligible values of 0.01 and 0.03 atoms per formula unit in the yttrium-dominant cores of the crystals to 0.18 and 0.14 atoms per formula unit in the neodymium-dominant rims, with similar enrichment in the hornfels material.

Bainbridgeite-(NdCe) thus does more than add a name to the mineralogical record. It provides a natural experiment in element sorting, showing how the subtle size preferences of individual rare-earth atoms can drive their separation into distinct structural sites as a magmatic system evolves. Because rare-earth elements underpin modern technologies from permanent magnets to phosphors, understanding the crystallochemical rules that govern their partitioning in alkaline complexes has relevance well beyond mineral taxonomy. Mont Saint-Hilaire, which has yielded dozens of new species since quarrying began, once again demonstrates its unmatched ability to preserve the chemistry of late-stage fluids in exquisitely rare and structurally intricate minerals, and the mckelveyite group, now spanning five formally described parts, continues to reveal how nature organizes some of the rarest elements in the crust.

Subject of Research: Crystal chemistry and site-specific rare-earth element partitioning in a new mckelveyite-group carbonate mineral

Article Title: Mckelveyite group minerals – Part 5: Bainbridgeite-(NdCe), Na2Ba2NdCe(CO3)6●3H2O, a new neodymium and cerium-dominant species from Mont Saint-Hilaire, Canada

Article References: Lykova, I., Rowe, R., Poirier, G., Friis, H., Ojaste, K., & Barnes, S. (2026). Mckelveyite group minerals – Part 5: Bainbridgeite-(NdCe), Na 2 Ba 2 NdCe(CO 3 ) 6 ●3H 2 O, a new neodymium and cerium-dominant species from Mont Saint-Hilaire, Canada. European Journal of Mineralogy, 38(4), 419-429. https://doi.org/10.5194/ejm-38-419-2026

Image Credits: AI Generated

DOI: 10.5194/ejm-38-419-2026

Keywords: bainbridgeite-(NdCe), new mineral species, Mont Saint-Hilaire, mckelveyite group, rare-earth elements, neodymium, cerium, carbonate mineral, crystal structure, X-ray diffraction, alkaline complex, mineralogy

The study, published in the journal Climate of the Past, presents the first high-resolution, quantitative reconstruction of dust provenance in the EPICA Dome C ice core, one of the most celebrated climate archives on Earth. Led by Sibylle Boxho and Steeve Bonneville of the Université Libre de Bruxelles, the team analyzed rare earth element patterns in 279 samples of ancient dust spanning 33,700 to 2,800 years before present. Using a novel statistical unmixing algorithm called DEEPOT, they quantified for the first time exactly how much dust reached this remote inland site from each of the Southern Hemisphere’s major source regions, resolving changes on timescales of roughly a century.

The technical achievement lies in the chemistry of the lanthanoid series, the fourteen rare earth elements whose relative abundances act like a fingerprint for the rocks from which dust was derived. Traditional provenance work has relied on strontium, neodymium, and lead isotope ratios, but those methods demand relatively large sample masses, a serious problem at EPICA Dome C where dust fluxes plummeted by up to a factor of twenty-five from glacial to interglacial conditions. Rare earth element patterns, by contrast, capture multidimensional geochemical information from far smaller samples, and because the patterns of potential source areas differ subtly but consistently, a constrained least-squares model can decompose any measured dust sample into a weighted mixture of contributing sources.

To make the approach work, the researchers compiled a database of 245 rare earth element patterns from known dust source regions across the Southern Hemisphere: Patagonia and Tierra del Fuego, Central Western Argentina, the Puna-Altiplano Plateau, Southern Africa, Australia, New Zealand’s South Island, and the ice-free McMurdo Dry Valleys of Antarctica itself. Each ice core sample was then modeled as a linear combination of these end-members, with the constraint that all contributions must be positive, since physical proportions of dust cannot be negative. To guard against analytical uncertainty, the team ran 2,000 Monte Carlo simulations per sample, randomly perturbing measured concentrations within their error bars and recalculating the best-fit source mix each time. Only samples whose modeled patterns correlated strongly with the measurements, at a threshold corresponding to statistical significance, were retained, yielding 238 reliable reconstructions.

The headline result is strikingly clear. During the late Marine Isotope Stage 3, the Last Glacial Maximum, and Heinrich Stadial 1, roughly 65 to 75 percent of all dust deposited at Dome C came from Patagonia, with secondary contributions from New Zealand, Australia, Southern Africa, and the Puna-Altiplano. This dominance was remarkably stable, even as total dust flux began collapsing around 18,000 years ago. The explanation lies in the geography of the ice age world: the Patagonian Ice Sheet then stretched 2,090 kilometers along the Andes, grinding bedrock into fine glacial flour that braided rivers spread across vast outwash plains. With global sea level about 135 meters lower than today, an additional 763,000 square kilometers of continental shelf lay exposed, dry, and ready for the strong westerly winds to strip away.

New Zealand’s role emerged as a surprise. The country contributed an average of nearly 14 percent of dust at Dome C during the Last Glacial Maximum, making it the second-largest source, a finding that contrasts with earlier isotope-based studies that had argued against significant New Zealand input to East Antarctica. The researchers point to the extensive South Island ice sheet, an enlarged continental shelf of roughly 62,000 square kilometers, and cold, windy glacial conditions as factors that plausibly boosted New Zealand dust emissions to levels capable of reaching the deep interior of the continent. Modern trajectory modeling, they note, suggests New Zealand dust can still contribute between 14 and 32 percent of deposition at inland Antarctic sites.

Then, around 14,500 years ago, everything changed. The dust assemblage shifted decisively away from high-latitude glaciogenic sources toward lower-latitude ones. Patagonia’s share fell to an average of 43 to 53 percent during the Holocene, while Australia surged to become the second-most important supplier at 21 to 28 percent, the Darling Basin in particular. Southern Africa and the Puna-Altiplano each climbed to roughly 8 to 9 percent, and dust from the McMurdo Dry Valleys, essentially absent before 13,000 years ago, appeared as the Antarctic valleys deglaciated. The Holocene record also became far more variable, with source contributions fluctuating at high frequency in a way the stable glacial regime never did.

The drivers of this transition, the authors argue, were geological and hydrological rather than purely meteorological. The timing coincides with Meltwater Pulse 1A, a rapid episode of global sea-level rise that submerged vast tracts of the Patagonian and New Zealand continental shelves, permanently removing exposed, deflatable sediment from the wind’s reach. At the same time, the waning Patagonian Ice Sheet triggered a major reorganization of regional drainage: new channels opened, redirecting large portions of river catchments from the Atlantic to the Pacific, while rivers on the eastern flank of Patagonia shifted from braided to meandering forms. Together these changes starved the aeolian system of the fine sediment that had fed Antarctic dust for millennia. Crucially, the provenance shift was decoupled from the earlier, massive decline in total dust deposition between 18,000 and 15,000 years ago, which the researchers attribute instead to enhanced wet scavenging, rainout of particles along warmer, moister transport pathways.

Independent lines of evidence bolster the reconstruction. When the team converted their rare earth element-based source contributions into expected strontium and neodymium isotope ratios, the modeled values matched the sparse isotopic measurements from Dome C and other East Antarctic cores, clustering around less radiogenic signatures during the glacial period, consistent with fresh, mafic Patagonian and New Zealand lithologies, and drifting toward more weathered, radiogenic compositions in the Holocene as Australian and African inputs grew. Comparison with the EPICA Dronning Maud Land core, on the Atlantic side of the continent, revealed broadly synchronous millennial-scale changes but telling regional differences: the Atlantic-sector core received more Patagonian dust, while Dome C, deeper inland and in the Indian Ocean sector, received more Australian material, consistent with subtropical jet streams lofting low-latitude dust over the polar vortex during Rossby wave intrusions.

The broader significance extends beyond paleoclimate trivia. Mineral dust delivered iron to the Southern Ocean during glacial times, fertilizing marine productivity and helping draw down atmospheric carbon dioxide, so knowing precisely where that dust originated sharpens our understanding of the iron fertilization feedback that helped terminate ice ages. The study also demonstrates that sea-level rise and postglacial hydrological reorganization can durably rewire hemispheric dust cycles, a reminder that coastlines and river systems are active, threshold-sensitive components of the Earth system. As modern sea levels climb and hydrology shifts once again, the dust trapped in Antarctic ice offers a sobering preview of how quickly the planet’s connective tissue can be rearranged when the climate crosses a tipping point.

Subject of Research: Quantitative reconstruction of Southern Hemisphere dust provenance in Antarctic ice during the last glacial-interglacial transition

Article Title: Quantifying Southern Hemisphere dust sources during the Last Glacial-Interglacial Transition using rare earth elements in the EPICA Dome C ice core

Article References: Boxho, S., Vanderstraeten, A., Mattielli, N., Laruelle, G. G., Bory, A., Gabrielli, P., & Bonneville, S. (2026). Quantifying Southern Hemisphere dust sources during the Last Glacial-Interglacial Transition using rare earth elements in the EPICA Dome C ice core. Climate of the Past, 22(9), 1655-1674. https://doi.org/10.5194/cp-22-1655-2026

Image Credits: AI Generated

DOI: 10.5194/cp-22-1655-2026

Keywords: EPICA Dome C, ice core, dust provenance, rare earth elements, Last Glacial Maximum, Patagonia, Australia, Puna-Altiplano, sea-level rise, Southern Hemisphere circulation, last deglaciation, Climate of the Past

The scientific case rests on a paradox that has puzzled researchers for years. The Laacher See region shows exceptionally high uplift rates on spatial scales of hundreds of kilometers, persistent seismic activity, and vigorous carbon dioxide degassing from springs and mofettes, gas vents that bubble mantle-derived CO2 straight out of the ground. The helium isotopic composition of these gases, with elevated 3He/4He ratios, demonstrates a significant contribution from the Earth’s mantle. Yet the shallow hydrothermal system above the residual magma reservoir appears to be surprisingly cold, despite the fact that the system beneath is clearly dynamic. Only drilling, the workshop participants concluded, can resolve this contradiction by sampling the fluids and host rocks at depth and by providing the first reliable heat flow measurements for the region.

The evidence for what lies beneath is extraordinary in itself. Plutonic ejecta clasts, fragments of rock torn from the walls of the magma system and hurled out during the eruption, are found in the pyroclastic deposits of the Laacher See volcano. These clasts include cogenetic carbonatite, a rare igneous rock rich in carbonate minerals, whose study transformed early hypotheses about the crustal origins of carbonatites by demonstrating their mantle-like carbon and oxygen isotopic composition. The carbonatite ejecta reach critical mineral levels of roughly 0.25 weight percent rare earth element and yttrium oxide, well above the global median for carbonatites of about 0.08 weight percent. This provides tangible evidence for magmatic pre-enrichment and hydrothermal redistribution of critical elements within the Laacher See magma plumbing system, and it hints at processes that, in older fossil systems, have produced world-class ore deposits.

Recent geophysical observations have sharpened the picture considerably. Deep low-frequency earthquakes, first detected in 2013, occur in persistent depth clusters and trace a subvertical channel structure between 10 and 45 kilometers depth through which CO2-rich fluids and possibly melt migrate upward. This transcrustal channel coincides with the location of the highest CO2 fluxes and the most elevated helium isotope ratios in the region, close to the village of Glees. Local earthquake tomography, drawing on a large-N passive seismological experiment with more than 500 stations deployed between 2022 and 2023, has resolved a cylindrical velocity anomaly beneath Laacher See with a diameter of about 3 kilometers, dipping roughly 53 degrees toward the south-southeast and reaching a depth of about 10 kilometers. Three-dimensional gravity inversion confirms a density deficit down to at least 9 kilometers depth, and receiver function analysis reveals strong upwellings of the crust-mantle boundary and the lithosphere-asthenosphere boundary beneath the region.

The eruption history adds urgency to the hazard questions. Volcanism in the East Eifel Volcanic Field began at the Rieden center around 460,000 to 430,000 years ago, migrated southeastward, and culminated in the VEI 6 eruption of Laacher See at 13,000 years ago, an event precisely dated by tree-ring-correlated radiocarbon and speleothem uranium-series methods. More than 350 eruptions occurred within roughly 700,000 years across the Eifel fields. Petrological studies show that the pre-eruptive reservoir was thermally and compositionally stratified, remained hot above 560 degrees Celsius for tens of thousands of years, and received a basanitic recharge with magma-mingling timescales of less than 400 days before the climactic eruption. That spontaneous response between recharge and eruption poses a serious challenge for hazard assessment in systems with long and irregular recurrence intervals.

Even more intriguing are the possible precursors. Mapping along the western slope of the Veitskopf scoria cone has identified diatreme breccias, structures interpreted as potentially CO2-driven explosive events that may represent precursor activity related to the ancestral Laacher See system. Remarkably large aligned tree trunks, one meter long and about 30 centimeters in diameter, are preserved near the base of these breccia deposits, along with charred plant remnants. Radiocarbon dating indicates the terminal diatreme breccia deposition occurred before 13,000 years ago, with a tree trunk minimum age of about 51,000 years. Evidence for cold, CO2-driven diatreme formation, combined with current deformation transients and occasional limnic gas bursts in the lake itself, including an eyewitness report from August 2022, suggests that long-lasting gas recharge into and release from subsurface CO2 reservoirs poses hazards that are currently widely disregarded, both in the Eifel and elsewhere.

The workshop process, funded in part by the International Continental Scientific Drilling Programme, brought together more than 80 participants from 10 countries and produced a clear two-phase strategy. Phase 1 comprises four shallow boreholes of 300 to 2000 meters depth. The first, planned near Glees as part of the ERC Synergy Project Archean Park, targets a CO2 mofette location about 1.6 kilometers northwest of the lake with a target depth of 300 meters, drilling planned for winter 2025 to spring 2026. A second site near Krufter Waldsee, about 3 kilometers southeast of the lake center, would core a maar structure whose lake sediments may preserve an unprecedented record of precursor events before the cataclysmic eruption. A third site would test links between surface fluid transients and deep low-frequency earthquakes, while a fourth would constrain volcano-tectonic subsidence associated with the 13,000-year-old eruption.

Phase 2, the aspirational deep hole of 3000 to 4000 meters, would penetrate and core the syenitic-carbonatitic intrusive carapace and its hydrothermal aureole at an anticipated depth of 4 to 6 kilometers at its top. This would be globally unique: direct sampling of fluids and rocks within an active silicate-carbonatite system, unmodified by the weathering, erosion, and metamorphic overprinting that complicate the study of older carbonatites. Such samples are the tangible evidence required to properly balance CO2 fluxes from degassing magma against CO2 sequestration in carbonatites and fluid-precipitated carbonates, a question with direct relevance to understanding both the global volcanic carbon budget and the feasibility of anthropogenic carbon storage in continental settings.

The stakes extend beyond pure science. Carbonatites are the primary resource for the rare earth elements needed for permanent magnets in the transition to a zero-emission economy, and silicate-carbonatite intrusions are globally recognized as major hosts for critical metal deposits. The Laacher See project would complement the ICDP REEDRILL project targeting the fossil Songwe Hill complex in Malawi by capturing mineralizing processes in the act of formation. Instrumented wells would also transform monitoring, using borehole thermometry, tiltmeters, geophones, optical fibers, and pressure sensors to detect weak precursor signals of magma ascent. With the region’s dense population, excellent infrastructure, and 200 years of prior research, the workshop participants concluded that Laacher See is an ideal test bed, one whose lessons will apply to distributed volcanic fields worldwide, from Auckland to Medina, where similar hazards lurk beneath deceptively calm landscapes.

Subject of Research: Scientific drilling of the actively degassing Laacher See volcano and its underlying silicate-carbonatite intrusion in the Eifel volcanic field, Germany

Article Title: Follow the CO2 – drilling into an actively degassing intraplate volcano underlain by a silicate–carbonatite intrusion

Article References: Dahm, T., Schmitt, A. K., de Silva, S., Fischer, T., Holzheid, A., Kukowski, N., Lavallee, Y., Sturm, A., & Troch, J. (2026). Follow the CO 2 – drilling into an actively degassing intraplate volcano underlain by a silicate–carbonatite intrusion. Scientific Drilling, 35(1), 1-20. https://doi.org/10.5194/sd-35-1-2026

Image Credits: AI Generated

DOI: 10.5194/sd-35-1-2026

Keywords: Laacher See, Eifel volcanism, scientific drilling, carbonatite, carbon dioxide degassing, intraplate volcanism, maar volcanoes, deep low-frequency earthquakes, rare earth elements, ICDP, magma reservoir, volcanic hazards

The mineral was approved by the International Mineralogical Association’s Commission on New Minerals, Nomenclature and Classification under proposal number IMA 2024-091, and carries the official symbol Xhu-Ce. Its name honors Professor Xianhua Li, an academician of the Chinese Academy of Sciences, in recognition of his contributions to research on early Earth and planetary evolution and, in particular, his recent advances in the geochronology, geochemistry, and resource development of the Bayan Obo deposit. The holotype specimen, catalogued as GMCTM2024012, is held at the Geological Museum of China in Beijing, while a co-type specimen resides in the crystal structure laboratory at China University of Geosciences, Beijing. These reference samples ensure that any future researcher can compare material against the defining specimens of the species.

Xianhuaite-(Ce) was found in two rock samples collected from different parts of the Bayan Obo complex. One specimen, BY-E2024-103, came from the East Orebody, where it occurs as black-brown megacrystalline aggregates at the contact between aegirine-type and dolomite-type niobium-rare earth-iron ores. The other, BY-EC2024-14, was collected from the East Contact Zone within dolomite-type ore. In that second sample, quantitative mineral mapping using a Tescan integrated mineral analyzer showed the rock is dominated by dolomite at nearly 72 percent by volume and magnetite at about 12 percent, with fersmite making up 8 percent. Xianhuaite-(Ce) itself accounts for a modest 0.40 volume percent, appearing alongside columbite-(Fe), aeschynite, fergusonite-(Ce), and small amounts of pyrochlore, phlogopite, barite, apatite, and other phases typical of skarn-altered assemblages.

Under the microscope and in hand specimen, the new mineral presents as irregular grains or tetragonal prisms ranging from tiny slivers of roughly 0.03 by 0.03 by 0.1 millimeters up to crystals of about 0.4 by 0.4 by 0.6 millimeters. It is dark brown to blackish brown in bulk, but thin fragments transmit a pale yellow-brown to brownish-red light. It shows an adamantine luster, a white streak, perfect cleavage on the {001} plane, and a conchoidal fracture, and it is brittle. Its Mohs hardness falls between 5 and 6, and micro-indentation testing yielded a mean Vickers hardness number of 469.5 kilograms per square millimeter at a 200-gram load. The calculated density is 5.23 grams per cubic centimeter, and the mineral shows no fluorescence under longwave ultraviolet light and no magnetic response.

Chemical analysis by electron probe microanalysis with wavelength-dispersive spectrometry, performed on a JXA-iHP200F instrument at 15 kilovolts and 20 nanoamperes, established the empirical formula. Normalized to 15 oxygen atoms per formula unit, it reads (K1.30Ba0.69Sr0.02)(Ce0.39La0.31Nd0.04Pr0.02Ca0.15Na0.09)(Nb4.75Fe0.13Ti0.09Mg0.04)O15. In plain terms, the large channel sites of the structure are filled mostly by potassium and barium, with a smaller site occupied chiefly by cerium and lanthanum plus minor calcium and sodium, while the octahedral framework sites are dominated by niobium with a little iron, titanium, and magnesium. Backscattered electron imaging confirmed the crystals are chemically homogeneous at the micrometer scale, and the simplified formula (K,Ba)2(Ce,La)(Nb,Fe)5O15 rounds to the ideal K2CeNb5O15.

The structural work is where the discovery becomes remarkable. Single-crystal X-ray diffraction on a fragment measuring just 0.02 by 0.02 by 0.01 millimeters, collected with molybdenum radiation on a Rigaku XtaLAB PRO-007HF diffractometer, revealed a tetragonal unit cell with a = 12.5355 angstroms, c = 3.9213 angstroms, and a volume of 616.19 cubic angstroms, in the centrosymmetric space group P4/mbm. The refinement converged to an R1 value of 0.0189 based on 427 independent reflections, an exceptionally good fit. The structure is a textbook tetragonal tungsten bronze framework: niobium-centered oxygen octahedra share corners to build a two-dimensional network in the horizontal plane, generating rings of four and five octahedra that line vertical channels running along the c axis. The larger five-membered channels host potassium and barium in ninefold coordination, while the four-membered channels accommodate cerium and calcium in twelvefold coordination.

Raman spectroscopy independently corroborated this architecture. The spectrum shows a prominent band near 853 wavenumbers assigned to vibrations of the NbO6 octahedra, additional peaks at 645 and 537 wavenumbers corresponding to niobium-oxygen stretching modes, and low-frequency features at 175, 135, and 81 wavenumbers characteristic of cation motions in tetragonal tungsten bronze phases. The absence of any peaks above 1000 wavenumbers is consistent with a structure containing no hydroxyl or water groups. Bond valence sum calculations further confirmed that the assigned oxidation states and site occupancies are internally consistent, with the B1 octahedral site modeled as roughly 95 percent niobium and 5 percent trivalent iron, matching the chemical analyses.

What does the mineral say about how Bayan Obo formed its enormous metal endowment? The deposit has been studied for decades, yet the mechanisms of niobium enrichment remain debated, largely because the niobium is scattered across at least 30 distinct mineral species rather than locked in one dominant host. The textural evidence from the East Contact Zone sample offers a clue: xianhuaite-(Ce), fersmite, and columbite-(Fe) occur as interstitial phases between magnetite grains, and both xianhuaite-(Ce) and fersmite contain relict pyrochlore inclusions inherited from an earlier mineralization stage. The authors argue these relationships are inconsistent with primary magmatic crystallization and instead point to precipitation from niobium-bearing fluids during a later hydrothermal overprint. The surrounding assemblage of forsterite, phlogopite, chlorite, and dolomite is characteristic of magnesian skarn systems formed when granite intrudes dolomitic host rocks.

The regional context strengthens that interpretation. The East Contact Zone experienced variable degrees of skarnization during the emplacement of Permian granites, a thermal event that apparently did not add new niobium to the system but likely remobilized niobium already present. Taken together, the mineral assemblages, textures, and geology suggest xianhuaite-(Ce) formed under fluid-dominated conditions during the Permian granitic event, recording the remobilization and redistribution of niobium rather than its original accumulation. The coarse-grained East Orebody sample lacks diagnostic assemblages for direct petrographic constraints, but regional geochronology indicates the Permian thermal event affected the entire district, so the researchers tentatively assign its xianhuaite-(Ce) to the same episode, while noting that direct dating is still lacking.

The discovery also resonates beyond geology. Synthetic compounds with the same ideal composition, K2CeNb5O15, belong to a family of tetragonal tungsten bronze materials studied for their physical properties, and laboratory work has documented temperature-driven symmetry transitions within this structural family. The natural mineral refines best in the centrosymmetric high-temperature form, P4/mbm, and intensity statistics support that choice. By capturing a structure long known only from synthesis, xianhuaite-(Ce) expands the known structural diversity of natural niobium minerals and provides new mineralogical constraints on how niobium behaves during the multistage evolution of one of the world’s most extraordinary ore deposits. For a metal critical to advanced technologies, every new clue about where and how it concentrates carries practical weight.

Subject of Research: Discovery and characterization of the new niobium mineral xianhuaite-(Ce) from the Bayan Obo deposit

Article Title: Xianhuaite-(Ce), K2CeNb5O15, a new niobium mineral from the Bayan Obo deposit, China

Article References: Yang, B., Xue, Y., Yang, L., Sun, N., Li, G., Yu, J., Yan, G., Liu, J., Zhao, Y., Meng, W., Chen, Z., Chen, L., Liu, Z., Yan, Z., Hou, X., Ao, X., & Wang, J. (2026). Xianhuaite-(Ce), K 2 CeNb 5 O 15 , a new niobium mineral from the Bayan Obo deposit, China. European Journal of Mineralogy, 38(4), 449-459. https://doi.org/10.5194/ejm-38-449-2026

Image Credits: AI Generated

DOI: 10.5194/ejm-38-449-2026

Keywords: xianhuaite-(Ce), Bayan Obo, niobium, new mineral, tetragonal tungsten bronze, rare earth elements, crystal structure, skarn, hydrothermal remobilization, mineralogy, Inner Mongolia, electron microprobe

Carbonatites are among the strangest rocks on Earth. They are igneous rocks composed of more than fifty percent carbonate minerals, yet they crystallise from molten carbonate rather than forming in oceans or lakes. They are volumetrically tiny, arising from extremely low degrees of partial melting of carbonated peridotite in the mantle, with melt fractions below roughly 0.05 weight percent. Despite their scarcity, carbonatites punch far above their weight economically: they host the highest rare earth element concentrations of any igneous rock type and have supplied the world with niobium, phosphate and light rare earths for nearly half a century. China’s Bayan Obo, the largest carbonatite-hosted rare earth deposit on the planet, illustrates the scale of what these rocks can deliver. With rare earth elements now classified as critical metals by most industrialised nations because of their indispensable role in green energy technologies, electric vehicle motors and wind turbines, every new carbonatite occurrence attracts immediate attention.

The Khaderpet carbonatite was discovered in 2002 by Rio Tinto Exploration during diamond-focused work on their 3-016 prospect in the Anumpalli Kimberlite Cluster. The plug intrudes an ultramafic lamprophyre known as aillikite, which itself was emplaced into Archaean granites, producing a distinctive granitoid breccia that geologists have likened to the carapace of a tortoise. Field relationships tell a clear story: the carbonatite contains angular clasts of the host granite but lacks any fragments of the lamprophyre, indicating that the carbonate magma arrived late, punching through the older breccia at the periphery of the complex. The rock weathers in the classic ‘panther skin’ pattern typical of carbonatites, and the surrounding granitoids display intense fenitisation, the brick-red alkali metasomatism produced by fluids exsolved from the carbonatitic magma. Caustic fusion of drill core from the prospect has even yielded good quality octahedral diamonds of transparent and grey varieties, adding a second commodity to an already unusual package.

Under the microscope, the Khaderpet carbonatite reveals an equigranular fabric dominated by calcite, which makes up ninety to ninety-five percent of the rock. The calcite grains display rhombohedral cleavage, twinkling relief and the high-order interference colours characteristic of carbonate under cross-polarised light. Scattered through this groundmass are accessory phases of considerable economic interest: euhedral fluorite crystals, apatite, phlogopite, garnet, magnetite and chromite, along with the rare earth bearing minerals monazite, titanite and allanite. These three minerals are the storehouses of the light rare earths, and their presence in thin section directly explains the exceptional whole-rock compositions. Flow banding in the finer grained portions of the rock, with aligned calcite crystals recording the movement of the magma, further attests to the intrusive, magmatic character of the body. Alteration of calcite to dolomite is common, particularly toward the rock margins.

The geochemistry is where Khaderpet truly stands out. Ten fresh outcrop samples analysed by X-ray fluorescence and inductively coupled plasma mass spectrometry show calcium oxide contents of 46.8 to 53.8 weight percent with negligible magnesium and iron, classifying the rock unambiguously as a calcio-carbonatite. Total rare earth element concentrations range from about 4100 to 4500 parts per million, of which the light rare earths contribute nearly everything, between 4092 and 4509 parts per million, while the heavy rare earths amount to a mere 19 to 24 parts per million. The ratio of light to heavy rare earths reaches values of 180 to 230, and the chondrite-normalised patterns show the steep, step-like profile typical of carbonatites worldwide, with a lanthanum-to-lutetium ratio of about 29 and an extraordinarily high lanthanum-to-ytterbium ratio near 282. Strontium concentrations of nearly 11,000 parts per million, barium around 900 parts per million, and elevated niobium, thorium and uranium complete the classic carbonatite trace element signature.

This extreme fractionation of light over heavy rare earths carries a profound petrogenetic message. It indicates that the Khaderpet magma formed by very low degrees of partial melting of carbonated mantle peridotite, followed by liquid immiscibility that separated the carbonate melt from its silicate sibling. Ratios of zirconium to hafnium, ranging from 85 to 115, and niobium to tantalum, from 110 to 270, show positive correlations consistent with a mantle origin. The primitive mantle-normalised trace element patterns display peaks for uranium, lanthanum, cerium and neodymium with troughs for rubidium and niobium, matching the fingerprints of metasomatised upper mantle sources. In short, the Khaderpet carbonatite is a genuine window into processes operating deep within the lithospheric mantle beneath the Eastern Dharwar Craton, a region whose thick lithospheric root has already proven fertile ground for more than 150 kimberlite and related intrusions.

Stable isotope analysis provides the final confirmation of primary character. Carbon and oxygen isotope measurements on five samples, performed at the Wadia Institute of Himalayan Geology, yield oxygen isotope values between 6.6 and 8.76 per mil and carbon isotope values between minus 7.45 and minus 6.33 per mil. These compositions fall squarely within the ‘primary igneous carbonatite’ box defined by decades of global data, overlapping the fields established for unaltered carbonatites from Precambrian terranes. Primary isotopic compositions essentially mean the rocks escaped crustal contamination and represent unmodified partial melts of the mantle. Combined with the petrography and trace element systematics, the isotope data leave little doubt that the Khaderpet carbonatite is a magmatic rock of deep origin, not a hydrothermal or secondary carbonate.

Perhaps the most consequential finding is economic. On geochemical discrimination diagrams plotting strontium-to-barium ratios and barium against total rare earth content, the Khaderpet samples plot in the ‘mineralised’ field, the same territory occupied by the Weishan rare earth deposit in China. The total rare earth content of Khaderpet exceeds that of several better-known south Indian carbonatites and approaches the values recorded at Hogenakkal, although it remains below the concentrations at Samalpatti, Pakkanadu and the Kamthai deposit, which to date is the only carbonatite-hosted rare earth occurrence in India proven feasible for mining. A drone magnetic survey has delineated an areal extent of roughly 100 by 200 metres with an average depth of 40 metres for the intrusion, but previous exploration drilled only a single shallow hole targeting diamonds. The authors argue that detailed drilling, ore characterisation and beneficiation studies are now essential to establish the order of magnitude of the rare earth oxide resource and to determine whether profitable extraction is possible.

The broader context amplifies the stakes. India currently hosts more than fifty confirmed and suspected carbonatite occurrences, and the Geological Survey of India has expanded its critical mineral exploration projects from 65 in 2020-2021 to 195 in 2024-2025, with several alkaline and carbonatite complexes among the targets. Recent discoveries across the Dharwar Craton, at Gollapalli in Telangana, Gundlupet in Karnataka and Krishtipadu in Andhra Pradesh, suggest the craton is far more carbonatite-fertile than previously recognised. The Khaderpet occurrence carries a double dividend: if the rare earth potential is confirmed, the site benefits from well-developed roads, water infrastructure and abundant local labour, and development would create employment while adding to national rare earth production. The study also issues a practical warning for explorers: carbonatites can hide alongside kimberlites, so any investigation of mantle-derived exotic rocks in the Indian Shield should watch carefully for associated carbonate intrusions. A small plug in a farmer’s field may yet prove to be a strategic national asset.

Subject of Research: Geochemistry and economic potential of a light rare earth element enriched carbonatite intrusion associated with kimberlitic rocks in the Eastern Dharwar Craton, India

Article Title: Geochemical studies and economic perspective of light rare earth element (LREE) enriched carbonatite from Khaderpet, Eastern Dharwar Craton

Article References: Phani, P. R. C., & Sengupta, P. (2026). Geochemical studies and economic perspective of light rare earth element (LREE) enriched carbonatite from Khaderpet, Eastern Dharwar Craton. Discover Geoscience, 4(1), Article 308. https://doi.org/10.1007/s44288-026-00663-7

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00663-7

Keywords: carbonatite, rare earth elements, LREE, kimberlite, Dharwar Craton, India, geochemistry, stable isotopes, monazite, critical minerals, diamonds, mineral exploration