Volume 110, Issue 6

The mindat.org website (Mindat) has been operating since October 2000 as a free, crowd-sourced, and expert-curated database particularly focused on mineral species and their occurrences worldwide. The project has transformed from a hobbyist site in the beginning into a resource that has found use in various scientific research projects and educational programs. Together with other open data resources, Mindat has helped accelerate scientific discoveries in many fields, such as mineral evolution, mineral ecology, and the co-evolution of the geosphere and biosphere. Recently, through open data efforts, machine interfaces and software packages have been established to enable flexible data discovery and download from Mindat. We assume that the data access and usage will further scale up in the next years. Although Mindat is curated by a team of geoscience and database experts across the world, the crowd-sourced records in Mindat possess some bias. In this paper, we first present an overview of the primary data subjects in Mindat and then give extensive details about the characteristics and partiality of three of the most popular data subjects: locality, mineral species, and mineral occurrence. In the discussion, we also give an outlook on appropriate data usage and future extension of data records. We hope users can obtain a more comprehensive view of the Mindat database through this paper and thus better plan their data use. We also hope more people will be inspired to contribute to the data curation work to make Mindat a sustained data ecosystem for geoscience research.

The occurrence of periclase in contact-metamorphosed dolomite rock at modest temperature and pressure indicates an infiltration of H 2 O because of the otherwise high temperature required for the reaction dolomite → periclase + calcite + CO 2 . We conducted experiments on the breakdown of dolomite in the presence of H 2 O at 700 °C, 100 MPa. Grains of dolomite, 175–250 μm in radius, were heated for up to 32 days (32 d). Rims of multigrain calcite and periclase formed around dolomite cores, with ∼50% of the dolomite replaced in 32 d. The growth of the rim is similar to that for previous experiments conductedwith cores of dolomite rock and follows a square root of time (t) $(\sqrt{t})$relation. The decrease in dolomite-core radius with t $\sqrt{t}$suggests that the rate is controlled by diffusion of CO 2 and H 2 O through the reaction rim. The results can be modeled by the topochemical or “shrinking-core” model, in which the unreacted grain core radius shrinks as r=r0−κt $r=r_0-\sqrt{\kappa t}$with a kinetic parameter κ of 6.76 ± 0.6 × 10 −4 μm 2 /s (0.0213 mm 2 /y). The model predicts that dolomite grains up to 2 mm in radius would disappear in <200 y. In a rock undergoing metamorphism at the conditions of the experiments, the reaction zone grows to a width ranging from <2 mm to >800 mm, depending on the radius of the grains in the rock. The porosity grows rapidly, and CO 2 is released abundantly at the beginning of the reaction near the leading edge of the periclase isograd. The shrinking-core process occurs as long as the intergranular fluid is H 2 O rich, requiring a modest minimum flux sufficient to displace the evolved CO 2 . The common replacement of periclase by brucite observed in nature was not seen in our experiments. Rather, the quench phase was the magnesium-carbonate hydrate nesquehonite, suggesting the brucite forms only in very CO 2 -poor fluid.

The influence of Al substitution on the elastic properties of stishovite and its transition to post-stishovite is of great importance for interpreting the seismic wave velocities of subducted mid-ocean ridge basalt (MORB) within the mantle transition zone and the lower mantle. However, atomistic mechanisms of Al substitution effects on the transition and its associated elasticity remain debated. Here synchrotron single-crystal X-ray diffraction measurements have been performed at room temperature on Al1.3-SiO 2 [1.3 mol% Al in the chemical formula of Si 0.965(3) Al 0.041(1) O 2 H 0.017(4) ] and Al2.1-SiO 2 [2.1 mol% Al in Si 0.948( 2 ) Al 0.064(1) O 2 H 0.018(3) ] crystals in diamond-anvil cells with Boehler-Almax designed anvils up to 38.0 and 28.5 GPa, respectively. Analyses of the diffraction patterns show that a transformation from stishovite (space group P 4 2 / mnm ; No. 136) to CaCl 2 -type post-stishovite (space group Pnnm ; No. 58) is accompanied by splitting of O coordinates. The Al substitution in stishovite results in a faster decrease in the O coordinate, softer apical (Si,Al)-Obonds, and a softer and less distorted (Si,Al)O 6 octahedron under compression. This leads to reduced adiabatic bulk modulus ( K S ), shear modulus ( G ), shear wave velocity ( V S ), and compressional wave velocity ( V P ) in the stishovite phase, explaining seismic wave perturbations in the mantle transition zone. Together with Raman data, Landau theory modeling shows that Al substitution increases the order parameter and excess free energy, stabilizing the post-stishovite phase at lower pressures. Correlation between elasticity and octahedral distortion index ( D ) reveals that at certain D , the Al substitution reduces K S , G , V S , and V P of the stishovite phase while increasing G , V S , and V P of the post-stishovite phase. Importantly, the maximum shear reduction is slightly enhanced at D = 0.00620(9) at the transition point. Our results help explain the seismically observed small-scale V S anomalies beneath subduction regions in the shallow lower mantle where Al,H-bearing stishovite undergoes the post-stishovite transition.

Quartz chemistry is important for revealing fluid sources and evolution in hydrothermal deposits, but such information is lacking for many epithermal systems and deposit types. To investigate quartz chemistry in this system further, we collected representative samples of quartz from adularia-sericite epithermal Ag deposits in China and determined their chemical compositions. In adularia-sericite epithermal Ag-bearing systems, magmatic quartz from porphyry intrusions and host subvolcanic rocks displays SEM-CL spectral peaks at 360 and 415 nm and exhibits homogenous CL or weak zonal textures (alternating growth zones within individual quartz crystals). Trace elements in magmatic quartz have the lowest Sb concentrations (median = 0.1 ppm; n = 80). Hydrothermal quartz can be classified into type I and type II by CL false color and CL spectral peaks. Hydrothermal type I quartz has spectral peaks at 360 and 415 nm; it exhibits zonal or sector textures and is associated with base metal sulfides and minor Ag mineralization. Such hydrothermal type I quartz has low Sb concentrations (median = 4.5 ppm; n = 839), contains liquid-rich fluid inclusions, and is formed by cooling. The cooling trend is indicated by a positive correlation between the concentrations of Sb and Al, as well as between Li and Al. Hydrothermal type I quartz has an Fe center by electron spin resonance, whereas other centers are missing or weak at room temperature. In general, hydrothermal type II quartz mantles type I quartz. Hydrothermal type II quartz has an ultrahigh-intensity peak (by several orders of magnitude) at 580 nm, zonal textures, and is associated with abundant Ag mineralization. Hydrothermal type II quartz has the highest Sb concentrations (median = 71 ppm; n = 185), which remain constant as Al decreases on an Sb vs. Al plot. This quartz has colloform, bladed, or zonal textures and contains coexisting liquid- and vapor-rich fluid inclusions indicative of boiling. Additionally, this quartz has a significantly higher E’1 center intensity, suggesting a high concentration of oxygen vacancies associated with rapid crystallization. The mineral paragenesis, analytical results, and geochemical models show that, in these Ag-bearing epithermal systems, hydrothermal type I quartz associated with base metal sulfides precipitated during cooling, whereas subsequent growth-zoned hydrothermal type II quartz with high Sb concentrations and Ag-minerals precipitated during boiling. These results suggest that the CL texture and spectra, trace elements, and electron spin resonance data of quartz could identify veins with potential for Ag mineralization in epithermal systems.

Regolith-hosted rare earth element (REE) deposits are the world’s primary source of heavy REEs (HREEs) critical to the global clean-energy transition. Previous studies suggested that REEs in regolith-hosted deposits are largely inherited from their parent granites. However, several HREE-dominated deposits occur in the weathering crusts of light REE (LREE)-enriched granites, where the mechanisms of REE fractionation remain poorly understood. Also, the conventional mining method of regolith-hosted REE deposits has limited efficiencies in REE recovery while causing enormous environmental contamination. Herein, we have investigated the distribution and speciation of Y and REEs in three representative regolith-hosted REE deposits (i.e., Gucheng and Shangyou, HREE-dominated; Renju, LREE-dominated) as well as Y-sorbed birnessite from batch experiments. Our results show that birnessite in all three deposits is a minor constituent but contains anomalously high concentrations of REEs and contributes to 25.3, 23.4, and 26.5% of the HREE contents of mineralized saprolites. Measured Y K -edge X–ray absorption spectroscopic data suggest that Y 3+ (representing HREE 3+ ) is adsorbed on birnessite as YO 8 complexes in all three deposits but via different linkages: i.e., the bidentate corner-sharing mode in the HREE-dominated deposits but a mixture of both bidentate corner-sharing and edge-sharing modes in the LREE-dominated deposit. These binding mechanisms are also observed in Y-sorbed birnessite prepared at different ionic strengths. Therefore, different binding mechanisms of Y and HREE sorption on birnessite together with its preferential adsorption of HREE not only are responsible for the formation of HREE-dominated deposits from LREE-enriched granites but have important implications for the sustainable development of regolith-hosted REE deposits.

Two reflection twins are known in the literature for galena: on {111} (spinel twin), frequent, and on {114}, rare and lamellar. The galena structure is highly pseudo-symmetric with respect to a reflection about {111}: at the composition plane, the lead and sulfur coordination change from octahedral to trigonal prismatic, without modification of the bond distances but with a shrinkage of the non-bonding Pb-Pb and S-S distances. The coordination around the composition plane of the {114} twin is instead broken, with too short non-bonding Pb-Pb and S-S distances and empty regions that justify the rarity of this twin. The composition plane is, however, highly reminiscent of the interface between galena modules in the lillianite homologous series, although the cell-twin operation active in that case is a reflection on a different plane, {113}. In lillianite and related structures of the PbS-Bi 2 S 3 phase diagram, coalescence of Pb sites corresponding to too short non-bonding distances allows for partial heterovalent Pb 2+ -Bi 3+ substitution. Given the similarity of the composition plane of the {114} twin, structural adjustments, possibly with a role played by impurities, may explain the formation of this twin, whose lamellar nature is also reminiscent of the polysynthetic cell-twinning in the lillianite homologous series. Because the {114} twin was only reported in previous morphological investigations and was never confirmed by diffraction studies, the hypothesis that this rare twin may actually correspond to {113}, i.e., the macroscopic counterpart of the well-known homologous series obtained by cell-twinning on the same plane, cannot be ruled out. The relative orientation of the twinned crystals of the two twins is, however, too different to support this hypothesis.

The structural evolution and compressibility of ordered and disordered ankerite were investigated at pressures up to ∼25 GPa using synchrotron single-crystal X-ray diffraction in a diamond-anvil cell. Ordered ankerite (space group R 3 ) undergoes a discontinuous phase transition between 12.15 and 13.45 GPa to a high-pressure structure called ankerite-II (space group P 1 ) that has Ca in an eightfold coordination. Disordered ankerite ( R 3 c space group) does not undergo a phase transition in the investigated pressure range. A Birch-Murnaghan equation of state was used to fit the volume compressibility. Ordered ankerite [ K 0 V = 95(1) GPa, K ′ = 3.8(3)] appears slightly more compressible than disordered ankerite [ K 0 V = 99(1) GPa, K ′ = 2.7(1)]. The phase transition in ordered ankerite has a change in volume of ∼0.6% and K 13.45 V = 110(11) GPa, K ′ = 7(3) for ankerite-II. The possible significance of this different behavior of ordered and disordered ankerite is discussed.

Porphyry Cu deposits in collisional orogens are new targets for modern mineral exploration. Aseries of post-collisional (Miocene; 22–12 Ma) porphyry copper deposits with Cu reserves over 45 Mt have been discovered in the Gangdese magmatic belt, southern Tibet. These magmas were derived from the partial melting of sulfide-bearing Tibetan juvenile lower crust and were well primed for porphyry Cu deposits, having high oxidation states and being rich in volatiles such as water, S, and Cl. However, only some plutons ended up with economic ore concentrations. We measured the igneous zircon water contents of ore-related and barren high Sr/Y magmas in the Gangdese belt, southern Tibet, and found that magmas that produce giant porphyry Cu deposits have lower zircon water contents than barren and small-deposit related magmas. Combined with previous studies of fluid inclusions, magmatic breccias, apatite geochemistry, and thermal histories, which demonstrated higher initial water content in causative porphyries such as the giant deposits of Qulong and Jiama, we believe that the lower zircon water content may be attributed to these magmas experiencing faster cooling and sudden depressurization of a large, primed, volatile-saturated or supersaturated mid-to-upper crustal magma chamber, which led to rapid and voluminous volatile exsolution and fluid discharge. These processes caused intense hydrothermal alteration and large ore deposition. In contrast, magmas that experienced slow cooling and deep emplacement would undergo steady-state degassing and weak alteration. The variable intrusive and thermal histories across the Gangdese intrusions reflect the interplay between surface and lithospheric dynamics within the Himalaya-Tibet orogen. Our findings suggest that the differences in zircon water content reflect the emplacement rate and depth of each granitic body and, therefore, may serve as an indicator for tectonics and the potential for mineralization.

Römerite, a triclinic hydrous sulfate in the P 1 space group with the chemical formula Fe2+Fe23+SO44⋅14H2O, $\mathrm{Fe}^{2+} \mathrm{Fe}_2^{3+}\left(\mathrm{SO}_4\right)_4 \cdot 14\left(\mathrm{H}_2 \mathrm{O}\right),$is of potential interest in studies of planetary environments, with particular relevance to Mars and the icy jovian satellites. Past work has indicated the presence of hydrous sulfates on said bodies, and the mixed-valence iron in römerite’s structure makes the mineral a worthwhile end-member composition in thermodynamic models. Such models should be constrained by measurements at the low temperatures relevant to the planetary environments in question. We characterized single crystals of römerite with time-domain Mössbauer spectroscopy, Raman spectroscopy, and X-ray diffraction methods. Through our X-ray diffraction experiment, we refined the unit-cell parameters of the crystal between 100 and 300 K. The resulting temperature-variant lattice parameters and volumes are reported and are fit by physical and empirical models of the thermal expansion coefficient. The physical model considered, a Debye model of thermal expansion, provides estimates of additional thermodynamic parameters: the ratio of the bulk modulus at 0 K and 1 bar to the thermodynamic Grüneisen parameter ( K 0,0K /γ th ), the volume at 0 K and 1 bar ( V 0,0K ), and the Debye temperature (θ D ).

Ezochiite was described as a newly discovered platinum-group mineral in the thiospinel group having an ideal formula of Cu + (Rh 3+ Pt 4+ )S 4 (Nishio-Hamane and Saito 2024), but the data presented show it is a platinian cuprorhodsite, Cu(Rh,Pt) 2 S 4 (Cabri et al. 2023; Rudashevsky et al. 1985). Similarly, Nishio-Hamane et al. (2024) describe shiranuiite as a new mineral having an ideal formula of Cu + (Rh 3+ Rh 4+ )S 4 on the basis of assumed valences. Thus, instead of weighing the significance of chemical substitution in a PGE-dominant thiospinel, the readership is instead burdened with accepting that there are three potential minerals with virtually identical crystal structures and similar, but supposedly distinct, chemical compositions. In the absence of any new, compelling data, particularly regarding the valences of the ions present in both ezochiite and shiranuiite, it is argued that both are not new mineral species but instead represent varieties of cuprorhodsite.

Shock recovery experiments were performed using a two-stage light gas gun to clarify the progressive deformation microstructures of calcite at the submicrometer scale concerning pressure. Decaying compression pulses were produced using a projectile that was smaller than the natural marble target. In two experiments, natural marble samples were shocked to 13 and 18 GPa at the epicenters of the targets. Calcite grains shocked in the pressure range of 1.1–18 GPa were examined using polarized light microscopy and (scanning) transmission electron microscopy. The density of free dislocations in the grains shocked at 1.1–2.2 GPa [10 8–9 (cm −2 )] is comparable to that of unshocked Carrara calcite grains. Subparallel bands of entangled dislocations <1 μm are formed at 4.2 GPa, and strongly entangled dislocations spread throughout the focused ion beam (FIB) sections at 7.3–18 GPa. Dislocations selectively nucleate and entangle near the slip planes at pressures above ∼3 GPa, corresponding to the transition from sharp extinction to undulatory extinction, according to the microstructural evolution with shock pressure. Above ∼6 GPa, the dislocations nucleated homogeneously throughout the calcite crystals. The dislocation microstructure in a calcite grain collected from the asteroid Ryugu particle is similar to that of the experimentally shocked calcite at 4.2 GPa. The estimated pressure of 2–3 GPa, determined through fault mechanics analyses and the presence of dense sulfide minerals in the Ryugu particles, is in line with this pressure.

Hanswilkeite, KFe 3+ S 2 , is a new potassium-rich natural sulfide discovered in the pyrometamorphic suite of the Hatrurim Formation, southern Negev Desert, Dead Sea basin, Israel. The mineral occurs in sulfide-calcite assemblages confined to black-colored calcite-spurrite marbles. It forms single-crystal grains up to 1 mm in size, isometric to lath-like, and often intergrown with a less-common rasvumite, KFe 2 S 3 . Associated minerals include srebrodolskite, tilleyite, fluormayenite, cuspidine, fluorapatite, old-hamite, pyrite, and andradite.Macroscopically, hanswilkeite has a deep-purple color, dull metallic luster, and brown-black streak. The Mohs hardness is 2. Moderate cleavage was observed along the c -axis. The calculated density is 2.654 g·cm− 3 . The Raman spectrum contains the following bands: 379, 357, 289, 236, 167, 131, and 124 cm −1 . In reflected light, the mineral has very strong pleochroism from yellow-pink to dark-gray. Anisotropy is very strong, ΔR 589 = 69%. Reflectance values for COM required wavelengths measured in air, R max / R min (λ, nm) (%): 16.0/9.2 (470); 19.6/9.3 (546); 18.5/9.0 (589); 32.0/9.3 (650). Chemical composition (electron microprobe, average of 6 points, wt%): K 23.78, Ca 0.44, Fe 34.75, Mn 0.60, Zn 0.47, S 39.46, Total 99.5, which corresponds to empirical formula (K 0.98 Ca 0.02 ) 1.00 (Fe 1.00 Mn 0.02 Zn 0.01 ) 1.03 S 1.98 (Σ = 4 apfu) or ideally KFe 3+ S 2 . Single-crystal X-ray diffraction shows that the mineral is monoclinic, space group C 2/ c (#15), with unit-cell parameters a = 7.0914(5), b = 11.3154(5), c = 5.3992(3) Å, β = 113.244(7)°, V = 398.08(4) Å 3 , and Z = 4. Strongest lines of X-ray powder diffraction pattern [ d in Å(I)( hkl )]: 5.68(100)(020,110); 3.270(31)(130); 3.227(29)(111); 2.921(45)( 2 21); 2.510(12)(131); 2.198(12)(132); 1.880(10)(330). The crystal structure has been solved and refined to R 1 = 0.038 for 454 unique observed reflections [ I ≥ 2σ( I )]. The structure consists of infinite chains of edge-sharing tetrahedra [FeS 4 ] − centered with Fe 3+ ; the sulfide chains are linked by K + ions. Hanswilkeite is the third discovered dithioferrate mineral: a sulfosalt that contains [FeS 2 ] − anion with iron in Fe 3+ state. Other known natural dithioferrates are erdite, NaFeS 2 ·2H 2 O, and raguinite, TlFeS 2 . Hanswilkeite has a synthetic counterpart and a group of related synthetic sulfides and selenides, which were well studied due to specific electrical and magnetic properties owed to their quasi-one-dimensional structures. The mineral can be considered as an indicator of an extreme potassium-rich environment superimposed onto anhydrous and oxidizing formation conditions. The association with oldhamite is herein discussed in view of super-reduced conditions previously supposed for oldhamite geosynthesis.

Porphyry-style hydrothermal alteration has long been recognized in the Delamerian Orogen, Southeastern Australia. However, the fertility of porphyry prospects in this belt, including the Anabama Hill, remains elusive, due to intermittent exploration activities and sparse exposure. Recent significant discoveries of porphyry-epithermal Cu-Au deposits in the adjacent Stavely Arc have led to renewed exploration interest. Reinvestigation of the Anabama Hill drill cores highlights that K-feldspar-rich and epidote-chlorite-dominated alterations are superimposed by extensive quartz-pyrite±chalcopyrite± molybdenite veins with white mica-quartz selvedges, related to early-middle Ordovician granitic stocks. Granodiorite and diorite hosts have diagnostic geochemical characteristics, including high Sr/Y, V/Sc ratios, and listric-shaped REE trends, implying amphibole-leading fractionation due to high water contents in primitive melts. LA-ICP-MS analyses show that characteristic element compositions, e.g., high Fe, Sr, Pb, U, and Bi and low Mg and REEs in the Anabama Hill epidote, and high Mn, Zn, Zr, and U and low Ca, Ba, and Pb in the chlorite, suggest the two minerals resulting from propylitic alteration rather than metamorphism. Compared to well-mineralized porphyry deposits, the epidote shows high Bi, Cu, Sr, Ti, Zr, and U, and the chlorite is high in Ti/ Sr and Al/ Si ratios, implying that they are most likely deposit-proximal or near a heat center. This is supported by intermediate to high temperatures of 200–420 °C calculated by chlorite geothermometer. Propylitic epidote and chlorite outside pyrite halos typically define geochemical shoulders by anomalous As-Sb and Mn-Zn highs, 1–1.5 km away from the mineralized centers. Given that most of the epidote and chlorite are intergrown with sulfides, their close proximity to a likely mineralized center accounts for low to moderate concentrations of distal pathfinder elements and subdued performances on the As-Sb and Mn-Zn fertility plots. Combined with bulk-rock results, proximal-fertility indicators recorded in epidote and chlorite provide encouraging implications for porphyry exploration in the Delamerian belt.