Far from being passive building blocks, minerals govern how Earth evolves and deforms, from seismic wave propagation to rock deformation and plate motion. This article explores how pressure builds within Earth and how minerals’ elastic response to compression and seismic waves reveals its internal structure. At higher stresses, beyond their elastic limit, deformation in minerals becomes permanent through crystal plasticity created by crystal defects and strongly enhanced by temperature. Over geological time scales, aggregates of crystals behave effectively as highly viscous fluids, enabling mantle convection and plate dynamics. Understanding Earth’s large-scale behavior therefore requires linking rock rheology to the mechanics of minerals down to crystal defects. By integrating observations, experiments, and models, we uncover the hidden rules connecting atomic interactions to planetary dynamics.

Minerals, especially crystalline ones, are generally anisotropic, meaning that some of their properties depend on direction. A spectacular example is cordierite, which, depending on the direction in which it is viewed in transmission, will appear purple or yellow.

Although stress-induced amorphization has recently been identified as a new and distinctive plasticity mechanism, a formal framework for its systematic application in materials engineering is still lacking. In this study, we establish that stress-induced amorphization in Mg2SiO4 forsterite exhibits all the key features of phase transformation plasticity, a well-known phenomenon that has enabled the development of high-performance materials. By analogy with the Transformation-Induced Plasticity (TRIP) effect, we introduce the concept of amorphous-TRIP (a-TRIP). We demonstrate that the a-TRIP features, in particular the orientation effect of stress-induced amorphization (particularly strong in forsterite), can be exploited to design materials with enhanced toughness, a notable advance for a class of materials traditionally limited by brittle behavior. Stress-induced amorphization has been observed in some systems as a plasticity mechanism. Here, simulations and microscopy reveal that stress-induced amorphization in forsterite exhibits the features of phase transformation plasticity.

Abstract Understanding the rheology of the Earth’s lower mantle is essential for modelling mantle convection and its consequences for the geodynamical, thermal and chemical evolution of the planet. However, the extreme pressure–temperature conditions, the long natural timescales, and the complexity of deep-mantle mineralogy make it difficult to constrain mantle viscosity from experiments alone. In this review, we examine an alternative approach based on mineral physics and multiscale numerical modelling, tracing its theoretical foundations and its development over the last decades. We first outline the key physical mechanisms governing plastic deformation in lower-mantle minerals—point defects, dislocations, diffusion, and grain-boundary processes—and the conditions under which they operate. We then summarize the major experimental advances that provide essential constraints for these models. Building on this foundation, we review the evolution of multiscale modelling strategies, from first-principles calculations of defect energetics and dislocation cores to mesoscale dislocation dynamics and polycrystal-scale formulations. Using ferropericlase and bridgmanite as archetypal examples, we show how successive developments have progressively linked atomic-scale mechanisms with macroscopic rheology under deep-mantle conditions. Finally, we discuss current limitations and outstanding challenges, including the scarcity of diffusion data at high pressures, uncertainties in defect chemistry, and the need to integrate multiphase and multimechanism deformation. Together, these elements provide a coherent view of the present capabilities of mineral-physics-based rheology and outline a roadmap for future efforts to improve our understanding of deep-mantle dynamics.

Mylonitic crustal rocks are often observed to contain micro-scale porosity, which in many instances can be found within regions of monomineralic quartz. This work documents micro-porosity that decorates quartz-rich shear bands of the Ikaria granite (Greece). Using scanning (SEM) and transmission (TEM) electron microscopy, we describe typical features of sub-micron, angular pores which commonly occur along grain boundaries in quartz mylonites. On grain boundary surfaces, we first observe that the pore-neighbour distance increases with pore size, suggesting pores to have coalesced over micrometric distances. Electron Backscatter Diffraction (EBSD) and high-angular resolution EBSD mapping, combined with focused ion beam cross-sectioning, confirm that faceted pores also decorate substructures, including some with high lattice distortions, presumably related to very high geometrically necessary dislocation densities (>= 1015 m(-2)). TEM observations do not confirm such high dislocation densities, but instead suggest that lattice curvature results from a residual elastic bending. TEM observations further reveal nanometric layers of amorphous silica, which embeds pores and wets grain boundaries as well as strain-induced intragrain boundaries. As indicated by SEM observations of a silica film on broken surfaces, amorphous silica is an intrinsic feature of pure quartz shear bands, here attributed to stress-induced mechanical amorphization.

Stress-induced amorphization has recently attracted attention as a potential deformation mechanism in ceramics, semi-conductors or minerals. Its activation is promoted when conventional plasticity, e.g. driven by dislocations, is inhibited. However, the mechanisms underlying this phenomenon are still unclear. Based on quantitative in situ TEM tensile testing of small-sized olivine bi-crystals, we demonstrate that stress-induced amorphization and grain boundary sliding can be activated under high stresses at room temperature in specimens with high angle grain boundaries. Low angle grain boundaries are less prone to this phenomenon. Varying the iron content in olivine demonstrates that iron inhibits amorphization and, consequently, promotes brittle failure. This contrast with the accepted view that iron promotes ductility but at high temperatures. These findings coming from natural minerals provide a novel approach regarding the control of the mechanical properties of hard materials at low temperatures.

Olivine is one of the most abundant silicate minerals in cosmic environments, occurring largely in amorphous form in the interstellar medium before crystallizing within protoplanetary disks. The kinetics and mechanisms governing this transition are central to understanding the thermal and chemical evolution of silicate dust. To investigate these processes at high spatial and structural resolution, we conducted an in situ transmission electron microscopy study on amorphous olivine thin films produced by pulsed laser deposition. Structural and chemical evolution during heating was monitored using selected-area electron diffraction, pair distribution function analysis, automated crystal orientation mapping, electron energy-loss spectroscopy, and aberration-corrected high-resolution transmission electron microscopy. The amorphous material begins to chemically reorganize at similar to 400 degrees C, where Fe2+ is oxidized to Fe3+ and nanoscale crystallites-presumably hematite-form within the glassy matrix. These crystallites appear to act as nucleation sites that promote subsequent olivine crystallization. Full crystallization occurs near 800 degrees C, yielding grains 50-150 nm in size. These observations provide direct nanoscale evidence for iron-assisted nucleation in amorphous olivine and offer constraints on the temperatures and pathways governing the crystallization of interstellar and protoplanetary silicate dust.

Mineral science emerged from humanity's earliest curiosity about the colors, hardness, and magnetic properties of stones and metals. Across centuries, observations by philosophers, naturalists, and early microscopists gradually revealed that these macroscopic traits arise from the hidden architecture of matter. The scientific revolutions of the 17th-20th centuries-from crystallography and optics to quantum mechanics and highpressure experimentation-established the atomic foundations of minerals and transformed mineralogy into a modern physical science. Today, mineral physics links nuclei, electrons, defects, and crystal structures to the behavior of Earth and planetary interiors. This sets the stage for this Elements issue, showing how insights across disciplines continue to shape our understanding of minerals from atoms to planets.

For potentially wider applications of ceramics with dislocation-tuned mechanical and functional properties, it is pertinent to achieve dislocation engineering in polycrystalline ceramics. However, grain boundaries (GBs) in general are effective barriers for dislocation glide and often result in crack formation when plastic deformation in ceramics is attempted at room temperature. To develop strategies for crack suppression, it is critical to understand the fundamental processes for dislocation-GB interaction. For this purpose, we adopt a model system of bi-crystal SrTiO3 with a 4 degrees tilt GB, which consists of an array of edge dislocations. Room-temperature Brinell indentation was used to generate a plastic zone at the mesoscale without crack formation, allowing for direct assessment of GB-dislocation interaction in bulk samples. Together with dislocation etch pits imaging and transmission electron microscopy analysis, we observe dislocation pileup, storage, and transmission across the low-angle tilt GB. Our experimental observations reveal new insight into dislocation-GB interaction at room temperature at the mesoscale.

The mechanical properties of amorphous olivine (a-olivine) deformed at room temperature are investigated in situ in a TEM under uniaxial tension using a Push-to-Pull (PTP) device. Thin films of a-olivine were produced by pulsed laser deposition (PLD). With or without electron irradiation, a-olivine films deform plastically, with a gradual transition that makes impossible the determination of a precise threshold. The strength attains values up to 2.5 GPa. The increasing strain-rate in load control results in an apparent softening with stress drop. The fracture strain reaches values close to 30 % without e-beam irradiation. Under electron illumination at 200 kV, the strength is lower, around 1.7 GPa, while higher elongations close to 36 % are obtained. Alternating beam-off and beam-on sequences lead to exceptionally large fracture strains equal to 68 % at 200 kV and 139 % at 80 kV. EELS measurements were performed to characterize the interaction between the electron beam and a-olivine. At a voltage of 80 kV, radiolysis accompanied by oxygen release dominates whereas at high voltage (300 kV) the interaction is dominated by knock-on type defects. Radiolysis is also the main interaction mechanism at 200 kV with low exposition which corresponds to most of our in situ TEM deformation experiments. To interpret the mechanical data, a simple 1D model has been developed to rationalize the load transfer between the PTP device and the specimen. The strain-rate sensitivity is 6 to 10 times higher when a-olivine is deformed under electron irradiation.

Micro-scale porosity is a feature commonly found in viscously deformed quartz-rich mylonites. However, the processes which may form such porosity are actively debated, and whether or not pores are formed syn-kinematically to shear zone activity remains uncertain. Yet, the production of micro-pores during rock deformation may have several critical implications, such as affecting the rock strength, possibly through the brittle-ductile transition, and/or providing fluid pathways through active shear zones.In this study we focus on quartz-rich shear bands produced during extensional deformation of a granitic pluton below the detachment of Ikaria (Cyclades, Greece). Nearby to the detachment, quartz aggregates are often decorated by micrometric and sub-micrometric pores, of which a large proportion adopt angular, crystallographically controlled shapes. Quartz in such decorated shear bands primarily deformed by crystal plasticity and underwent dynamic recrystallisation by subgrain rotation. Using a combination of standard and High-angular Resolution (HR) Electron Back-Scatter Diffraction (EBSD) analyses alongside Scanning and Transmission Electron Microscopy (SEM/TEM), we highlight that micro-pores decorate primarily grain boundaries, as well as some intragrain substructures including subgrain boundaries. EBSD analyses show that pore-decorated substructures are characterised by high (~4°) Kernel Average Misorientation (KAM), which describes the mean lattice misorientation of one EBSD pixel with respect to its closest neighbours. (HR)EBSD maps indicate a high lattice curvature gradient across these pore-decorated substructures, which can be seen by Geometrically Necessary Dislocation (GND) densities as high as 1015 per m2.TEM analyses of Focused Ion Beam (FIB) sections across grain and intragrain boundaries reveal that quartz contains free dislocation densities around 1013 per m2, which matches our (HR)EBSD estimates for the interior of grains and subgrains. GND estimates of some porosity-decorated subgrain boundaries are between 1014 to 1015 dislocations per m2, which are not visible in TEM. Instead, nm-scale layers of amorphous SiO2 are seen, into which porosity is often partially or fully embedded.Our results suggest that amorphous SiO2 and porosity are formed from the same process, since pores are embedded into amorphous SiO2. Furthermore, in the case of pore-decorated substructures where amorphous SiO2 is present, a factor other than dislocation climb likely accounts for their quartz lattice distortion, possibly related to a stress concentration. Although the origin of quartz amorphization remains a matter of discussion, we hypothesise a stress concentration which caused quartz to amorphize, followed by subsequent pore formation through fluid exsolution while stress was released. If this is the case, it would strongly suggest that pore nucleation occurred syn-kinematically in Ikaria.

The ductile deformation of strontium titanate SrTiO3 at low temperature (T less than or similar to 1000 K) is commonly associated with the activity of dislocations gliding in {110} slip planes. While dislocations with pure screw character keep essentially the same dissociated core structure in the whole temperature range, dislocations with edge character may adopt different atomic configurations, associated with different charge states and different mobilities. In this work we use atomic-scale simulations to investigate the core structure of charged and neutral edge dislocations. We report anew possible dislocation core that is charge-neutral, dissociated, and with the lowest Peierls stress reported so far, thus making it an efficient component of plastic deformation. In comparison, dislocations carrying a positive charge are slightly less mobile, while those with negative charge have a very low mobility. Our results indicate that glide of charge-neutral dislocations is favoured, and that they may locally acquire a charge by interacting with vacancies all while remaining glissile. Finally, we investigate edge dislocations that are dissociated in their climb plane, and confirm that they are energetically more favourable than their glissile counterparts. Computing the activation energy for the core transformation provides insight into the ductile-brittle transition.

The dehydration of antigorite is an important reaction in subduction zones with implications on both geochemical and geophysical processes. In this experimental study we focus on the onset of antigorite dehydration and investigate various chemical and physical parameters as possible drivers for the fluid release. We performed hydrostatic and co-axial Griggs experiments on antigorite serpentinites with variable chemical composition and microstructures at high-pressure and high-temperature conditions across the antigorite dehydration (1.5 GPa, 620–670 °C). For these conditions, our thermodynamic models predict the formation of olivine from magnetite decomposition and partial dehydration of antigorite. Detailed analyses of the run products reveal limited magnetite decomposition. Antigorite dehydration is restricted to samples that have been deformed. Nano-sized olivine and orthopyroxene formed locally in oblique dehydration bands and exhibit neither a clear crystallographic preferred orientation nor a topotactic relation with precursor antigorite. We argue that limited local dehydration in our experiments is related to strain and variations in reaction kinetics. Systematic investigation excludes mineralogical and chemical heterogeneities, and temperature gradients as reaction driving potentials. The structural relation of the dehydration bands suggests deformation-related dehydration, which is supported by numerical simulations that couple reaction kinetics with mechanical work rate and self-consistently predict dehydration bands. In this scenario, strain concentration due to applied axial stress locally increases the internal energy of antigorite to reach the activation energy of the dehydration reaction, enabling dehydration. This study highlights the importance of coupled mechanical and chemical processes and provides a mechanistic framework for deformation-induced dehydration of antigorite.

The rheology of Earth’s lower mantle plays a crucial role in shaping mantle convection and consequently in planetary evolution but is still under debate1. Propositions differ on the rheology of ferropericlase, whether it is stronger2 or weaker than bridgmanite1,3,4, the majority phase, but especially also on the mechanism by which bridgmanite deforms, either by pure diffusion creep1,5-7 or by pure dislocation climb2,8-10, or possibly in combination. Here we put the pure climb creep rheology to practice in mantle convection experiments with a novel focus on the role of atomic self-diffusion which is pivotal for the effectiveness in mantle convection of both diffusion creep and pure climb creep. From flow models that achieve a close fit to the inferred trend in slab sinking11, we introduce new constraints on the coefficient of self-diffusion. From this we show that pure climb creep prevails over diffusion creep in high-stress regions where the lower mantle deforms most strongly, i.e., ambient to sinking slabs and rising plumes, at last providing more clarity on the rheology of the lower mantle. An immediate implication is that the supposed ancient bridgmanite-enrichment below ~1000 km12,13 can only have survived in low-stress regions remote from sinking slabs and rising plumes and is subordinate for the style of mantle convection. The stress-dependence of pure climb creep leads to a dynamic viscosity field, a propensity for localization of flow in high-stress regions and fast plume ascent. Flow speeds are 1-2 cm/a ambient to sinking slabs and rising plumes and sub-cm/a flow elsewhere. In all, this predicts a much different dynamic role of the lower mantle than modelled so far in the investigating of Earth and rocky planets alike.

In this work, we investigate twist grain boundary (GB) energies and structures in Mg2SiO4 forsterite using atomistic simulations. We first present a new bond orientational order parameter allowing to highlight disordered regions in this low-symmetry crystal for which classical visualization tools are ineffective. Then we examine three GB planes, (010), (120) and (001), corresponding to the most favorable free surfaces of this crystal. We show that twist GB follow the same energy ordering as corresponding free surfaces. In addition, except for some misorientation angles and for the (120) GB plane, GB energies and structures are quite insensitive to microscopic translational degrees of freedom. The dislocation composition of low-angle twist GB can be related to γ-surfaces in the corresponding planes, and are in good agreement with first-principle calculations. It is also shown that the dislocation core structures in low angle twist GB can strongly differ from the ones of intracrystalline dislocations.

We propose a new procedure to extract information from electron tomography and use them as an input in a field dislocation mechanics. Dislocation electron tomography is an experimental technique that provides three-dimensional (3D) information on dislocation lines and Burgers vectors within a thin foil. The characterized 3D dislocation lines are used to construct the spatial distribution of the equivalent Nye dislocation density tensor. The model dislocation lattice incompatibility equation and stress balance equation are solved with a spectral code based on fast Fourier transform algorithms. As an output of the model, one obtains the 3D distribution of mechanical fields, such as strains, rotations, stresses, resolved shear stresses (RSSs) and energy, inside the material. To assess the potential of the method, we consider two regions from a previously compressed olivine sample. Our results reveal significant local variations in local stress fields and RSSs in various slip systems, which can impact the strong plastic anisotropy of olivine and the activation of different dislocation slip systems. It also evidences the built-up of kinematic hardening down to the nanometre scale.

Recent observations made by the authors revealed the activation of stress induced amorphization and sliding at grain boundary in olivine [1], a mechanism which is expected to play a pivotal role in the viscosity drop at the lithosphere-asthenosphere boundary and the brittle-ductile transition in the lithospheric mantle. However, there is a lack of information in the literature regarding the intrinsic mechanical properties and the elementary deformation mechanisms of this material, especially at time scales relevant for geodynamics. In the present work, amorphous olivine films were obtained by pulsed laser deposition (PLD). The mechanical response including the rate dependent behavior are investigated using a tension-on-chip (TOC) method developed at UCLouvain allowing to perform creep/relaxation tests on thin films at extremely low strain rates. In the present work, strain rate down to 10−12 s−1 was reached which is unique. High strain rate sensitivity of 0.054 is observed together with the activation of relaxation at the very early stage of deformation. Furthermore, digital image correlation (DIC), used for the first time on films deformed by TOC, reveals local strain heterogeneities. The relationship between such heterogeneities, the high strain rate sensitivity and the effect of the electron beam in the scanning electron microscope is discussed and compared to the literature.