Bingxu Hou

Biosignature detection remains a key challenge in astrobiology, yet robust mineral biosignatures remain limited. Raman spectroscopy is increasingly applied in planetary exploration, but its high-dimensional spectral information has not yet been fully exploited for biosignature discrimination using data-driven approaches. Here, we integrate Raman spectroscopy with interpretable machine learning to distinguish biotic from abiotic apatite, a ubiquitous phosphate mineral in terrestrial and extraterrestrial environments. We compile 331 apatite Raman spectra from abiotic and biotic sources and extract 21 band-resolved spectral features. Principal component analysis reveals systematic separation between abiotic and biotic endmembers. A random forest classifier achieves 96.8% accuracy on an independent test set. Robustness is confirmed by multiple validation schemes, including leave-one-source-out cross-validation across 60 independent data sources, indicating that model performance generalizes beyond source- or instrument-specific artifacts. Feature importance identifies two dominant controls: phosphate-band broadening as a structural indicator of disorder and the carbonate-band intensity as a chemical signature of substitution. Density-functional calculations reproduce these features in simulated spectra and indicate that carbonate substitution doubles phosphate-tetrahedral distortion and increases formation energies by two orders of magnitude. Mechanically, higher carbonate contents during biomineral apatite formation reduce crystallinity and broaden Raman bands. We propose that the trained machine-learning model and a two-feature decision map enable the rapid probabilistic discrimination of unknown apatite samples. Our Raman-based machine-learning framework establishes a broadly applicable and mission-relevant strategy for deep-time archives and future planetary missions.

The duration and dynamic evolution of surface water on Mars are key to understanding its past habitability. Utopia Planitia, Mars' largest northern basin, preserves mineralogical signatures of ancient aqueous activity that remains chronologically unconstrained. Here, we present the quantitative reconstruction of the Hesperian Ocean's lifecycle using spectral analysis of manganese (Mn) (hydr)oxides as paleohydrological markers. Our innovative Spectral Contrastive-Aware Network, a deep learning framework trained on 13,742 infrared spectra of Martian soil simulants, decodes short-wave infrared data from China's Zhurong rover and orbiters operated by ESA and NASA. We identify altitude-dependent Mn (hydr)oxides enrichment that forms a distinctive mineralogical "bathtub ring", indicating an ancient ocean with defined boundaries. By quantitative mapping the spatiotemporal distribution of these minerals, we reconstruct the ocean's origin, expansion, regression, and extinction. Depositional modeling constrains its lifespan to 0.8-1.5 million years, providing the chronometrically constrained evidence for sustained surface water stability during the Hesperian.

Chlorite plays an essential role in transporting water into the deep Earth. This study investigates the high-pressure behaviour of clinochlore up to ∼20 GPa at room temperature, using synchrotron X-ray diffraction and infrared spectroscopy. We identified a polytypic phase transition (from II b -2 to II a -1) at ∼9 GPa and a structural distortion at ∼12 GPa. The polytypic phase transition at ∼9 GPa is characterised by a significant reorganization of interlayer hydrogen bonding, transitioning to states of weakly bonded or non-hydrogen-bonded hydroxyl groups. The phase transition showed reversibility during the experiment. The structural distortion near 12 GPa indicates adjustments in the compression mechanism related to the hydroxyl groups across both the brucite-like and 2:1 sheets. The unit-cell volume of the low-pressure II b -2 phase was fitted to the second-order Birch-Murnaghan equation of state, and the resulting parameters are V ₀ = 710.9(3) Å ³ and K ₀ = 83.4(8) GPa. Our results exhibit a marked deviation from prior experimental findings, potentially attributable to the presence of Fe ²⁺ cation incorporation in the natural chlorite investigated in this work. This study emphasises the complexity of the hydroxyl group in response to pressure in layered-structure silicates.

Re-oxidation of Cr(III) in treated Cr-contaminated sites poses a considerable source of Cr(VI) pollution, necessitating stable treatment solutions for long-term control. This study explores the immobilization of Cr(VI) into chromite, the most stable and weathering-resistant Cr-bearing mineral, under ambient conditions. Batch experiments demonstrate chromite formation at pH above 7 and Fe(III)/Cr(III) ratios exceeding 1, with Fe(III) occupying all tetrahedral sites, essential for stability. A theoretical model is developed to evaluate the effects of pH and Fe(III)/Cr(III) ratios on chromite crystallinity, resulting in AI4Min-Cr, a publicly accessible platform offering real-time intelligent remediation strategies. To tackle the complexities of non-point source Cr pollution, we employ microbial methods to regulate on-site Eh and pH, optimizing chromite precipitation. Long-term stability tests confirm that chromite remained stable for over 180 days, with potential for magnetic separation recovery. This study presents a mineralogical strategy to address re-oxidation and Cr resource recovery in Cr-contaminated water and soil.

The complex environmental conditions at Cr-contaminated sites, characterized by uneven ion distribution, oxidants competition, and limited solid-phase mobility, lead to inadequate mixing of Fe-based reducing agents with Cr, posing significant challenges to the effectiveness of Cr remediation through Cr-spinel precipitation. This study investigates the distinct roles of Fe(II), Fe(III), and Cr(III) in Cr-spinel crystallization under ambient temperature and pressure. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray absorption near-edge structure spectroscopy, and Mössbauer spectroscopy were employed to elucidate the phase composition, microstructure, and ion coordination within the precipitates. Our findings indicate that Fe(II) acts as a catalyst in the formation of the spinel phase, occupying octahedral sites within the spinel structure. Under the catalytic influence of Fe(II), Fe(III) transitions into the spinel phase, occupying both the tetrahedral and the remaining octahedral sites. Meanwhile, Cr(III), due to its high octahedral site preference energy, preferentially occupies the octahedral sites. When Fe(II) or Fe(III) is present but does not meet the ideal stoichiometric ratio, a deficiency in Fe(II) leads to low yield and poor crystallinity of Cr-spinel, whereas a deficiency in Fe(III) can completely inhibit its formation. Conversely, when either Fe(II) or Fe(III) is in excess, the formation of Cr-spinel remains feasible. Furthermore, metastable Cr phases can be transformed into stable Cr-spinel by adjusting the Fe(II)/Fe(III)/Cr(III) ratio. These results highlight the broad range of conditions under which Cr-spinel mineralization can occur in environmental settings, enhancing our understanding of the mechanisms driving Cr-spinel formation in Cr-contaminated sites treated with Fe-based reducing agents. This research provides critical insights for optimizing Cr remediation strategies.

In the present study, we extensively explored the high-pressure behaviors and vibrational properties of amblygonite LiAlPO₄F with elevated pressures up to 34.3 GPa based on single-crystal X-ray diffraction measurements, Raman spectroscopy, and DFT calculations. The compressibility and elastic properties of amblygonite were determined first. Specifically, the obtained isothermal bulk modulus of LiAlPO₄F is 128(4) GPa and the triclinic phase exhibited anisotropic compression with axial compressibility β_c > β_a > β_b with a ratio of 1.11:1.00:1.20. The Raman spectra showed no indication of phase transformation and were used to obtained mode Grüneisen parameters. The average Grüneisen parameter for PO₄ tetrahedral sites was smaller than for the LiO₄F sites. Our results provide new insights into the phase stability and elastic properties of lithium-fluorite granites at extreme conditions.

Electron transfer is the most elementary process in nature, but the existing electron transfer rules are seldom applied to high-pressure situations, such as in the deep Earth. Here we show a deep learning model to obtain the electronegativity of 96 elements under arbitrary pressure, and a regressed unified formula to quantify its relationship with pressure and electronic configuration. The relative work function of minerals is further predicted by electronegativity, presenting a decreasing trend with pressure because of pressure-induced electron delocalization. Using the work function as the case study of electronegativity, it reveals that the driving force behind directional electron transfer results from the enlarged work function difference between compounds with pressure. This well explains the deep high-conductivity anomalies, and helps discover the redox reactivity between widespread Fe(II)-bearing minerals and water during ongoing subduction. Our results give an insight into the fundamental physicochemical properties of elements and their compounds under pressure.