Volume 106, Issue 12

Identifying magma fertility is an important task in ore genesis research. In this paper, we use apatite chemistry and Sr-Nd isotopes for such a study. The apatite crystals are from four Cretaceous coeval granodiorite intrusions with different styles of hydrothermal mineralization in the Tongling ore district, South China. The selected intrusions are Hucun, Dongguashan, and Xinwuli, which host both porphyry and skarn Cu deposits, and the Chaoshan, which hosts a skarn Au deposit. The abundances of apatite major and trace elements, such as Mn, V, Ce, S, F, Cl, and Cu, together with the whole-rock compositions, are used to decipher the oxidation states, volatile compositions, and Cu fertility of the parental magmas. The apatite Sr-Nd isotope compositions are used as tracers for the magma sources. The results show that: (1) the parental magma of the Au-mineralized intrusion is less oxidized and has higher S-Cl contents than those of the Cu-mineralized intrusions, and (2) the proportion of mantle-derived melt is much higher in the former than in the latter. The results also reveal that the Cumineralized intrusions have highly variable apatite Cu-Cl-S compositions. Specifically, the Xinwuli intrusion has much higher Cu but lower Cl-S contents in apatite than the other two intrusions, indicating that a Cu-rich magma is not universally required for the formation of hydrothermal Cu deposits. This study demonstrates that apatite is a robust petrogenetic and metallogenic indicator for porphyry and skarn-type Cu-Au ore deposits.

To investigate halogen heterogeneity in the subcontinental lithospheric mantle (SCLM), we measured the concentrations of Cl, Br, and I in kimberlites and their mantle xenoliths from South Africa, Greenland, China, Siberia, Canada, and Brazil. The samples can be classified into two groups based on halogen ratios: a high-I/Br group (South Africa, Greenland, Brazil, and Canada) and a low-I/Br group (China and Siberia). The halogen compositions were examined with the indices of crustal contamination using Sr and Nd isotopes and incompatible trace elements. The results indicate that the difference between the two groups was not due to different degrees of crustal contamination but from the contributions of different mantle sources. The low-I/Br group has a similar halogen composition to seawater-influenced materials such as fluids in altered oceanic basalts and eclogites and fluids associated with halite precipitation from seawater. We conclude that the halogens of the high-I/Br group are most likely derived from a SCLM source metasomatized by a fluid derived from subducted serpentinite, whereas those of the low-I/Br group are derived from a SCLM source metasomatized by a fluid derived from seawater-altered oceanic crust. The SCLM beneath Siberia and China could be an important reservoir of subducted, seawater-derived halogens, while such role of SCLM beneath South Africa, Greenland, Canada, and Brazil seems limited.

The 2019 Aguas Zarcas CM2 meteorite is the most significant carbonaceous chondrite CM2 fall since Murchison in 1969. Samples collected immediately following the fall and studied here provide the rare opportunity to analyze the bulk mineralogy of a CM2 largely free of terrestrial contamination. Bulk samples were analyzed by powder X‑ray diffraction (XRD), thermal gravimetric (TG) analysis, evolved gas analysis (EGA), and scanning electron microscopy (SEM) with an electron-probe micro-analyzer (EPMA). Water-extracted salts were analyzed by XRD. In hand specimen, the stones are brecciated and dominated by chondrule-rich and chondrule-poor lithologies, and locally, a matrix-rich lithology. Powder XRD patterns from multiple stones are dominated by reflections from serpentine group minerals, on which are superimposed reflections for ferrotochilinite, 1:1 regularly interstratified ferrotochilinite/cronstedtite, anhydrous silicates, calcite, pentlandite, pyrrhotite, and minor phases. Reflections for magnetite are present only from a metal-rich breccia clast. The serpentine XRD reflections from the chondrule-rich and chondrule-poor lithologies match those from 1 T cronstedtite, whereas those from the matrix-rich lithology match the 1 M polytype. Patterns with the 1 M polytype also show a distinct low-angle scattering to the serpentine basal reflection centered near 8.6 Å, the origin of which is obscure. Further matching of the known serpentines to the Aguas Zarcas data shows that cronstedtite accounts for a subordinate amount of the clays, and at least three other chemically and structurally distinct serpentines are likely present. A typical fragment of Aguas Zarcas yielded 0.6 wt% water-extractable salts. The powder XRD pattern of the dried water extract shows reflections for halite = NaCl; chlorartinite = Mg 2 (CO 3 )(OH)Cl·2H 2 O; thenardite = Na 2 SO 4 ; and sodium chlorate = NaClO 4 . The TG mass losses of 11.4 to 14.7 wt% are consistent with other CM2 chondrites. The gases detected by EGA are dominated by H 2 O and CO 2 , largely derived from the dehydroxylation and decomposition of serpentine and calcite, respectively. Also detected are gases with masses matching SO 2 /S 2 and H 2 S, which are primarily released below 480 °C, and a mass of 30, which matches the molecular weight of formaldehyde and ethane, shows a maximum at 376 °C. These organic gases likely derive from the pyrolysis of indigenous organic matter. Taken together, the millimeter-scale mineralogical study of Aguas Zarcas reveals a complex breccia dominated by CM2-like clasts. The detailed study of this meteorite, together with similar studies from a range of carbonaceous chondrites, provides the foundations for studying and interpreting the samples returned from the NASA OSIRIS-REx and JAXA Hayabusa2 missions.

Keplerite is a new mineral, the Ca-dominant counterpart of the most abundant meteoritic phosphate, which is merrillite. The isomorphous series merrillite-keplerite, Ca 9 NaMg(PO 4 ) 7 -Ca 9 (Ca 0.5 ◻ 0.5 ) Mg(PO 4 ) 7 , represents the main reservoir of phosphate phosphorus in the solar system. Both minerals are related by the heterovalent substitution at the B -site of the crystal structure: 2Na + (merrillite) → Ca 2+ + ◻ (keplerite). The near-end-member keplerite of meteoritic origin occurs in the main-group pallasites and angrites. The detailed description of the mineral is made based on the Na-free type material from the Marjalahti meteorite (the main group pallasite). Terrestrial keplerite was discovered in the pyrometamorphic rocks of the Hatrurim Basin in the northern part of Negev desert, Israel. Keplerite grains in Marjalahti have an ovoidal to cloudy shape and reach 50 μm in size. The mineral is colorless, transparent with a vitreous luster. Cleavage was not observed. In transmitted light, keplerite is colorless and non-pleochroic. Uniaxial (−), ω = 1.622(1), ε = 1.619(1). Chemical composition (electron microprobe, wt%): CaO 48.84; MgO 3.90; FeO 1.33; P 2 O 5 46.34, total 100.34. The empirical formula (O = 28 apfu) is Ca 9.00 (Ca 0.33 Fe 0 2 . + 20 ◻ 0.47 ) 1.00 Mg 1.04 P 6.97 O 28 . The ideal formula is Ca 9 (Ca 0.5 ◻ 0.5 )Mg(PO 4 ) 7 . Keplerite is trigonal, space group R 3 c , unit-cell parameters refined from single-crystal data are: a = 10.3330(4), c = 37.0668(24) Å, V = 3427.4(3) Å 3 , Z = 6. The calculated density is 3.122 g/cm −3 . The crystal structure has been solved and refined to R 1 = 0.039 based on 1577 unique observed reflections [ I> 2σ( I )]. A characteristic structural feature of keplerite is a partial (half-vacant) occupancy of the sixfold-coordinated B -site (denoted as CaIIA in the earlier works). The disorder caused by this cation vacancy is the most likely reason for the visually resolved splitting of the ν 1 (symmetric stretching) (PO 4 ) vibration mode in the Raman spectrum of keplerite. The mineral is an indicator of high-temperature environments characterized by extreme depletion of Na. The association of keplerite with “ REE -merrillite” and stanfieldite provides evidence for the similarity of temperature conditions that occurred in the Mottled Zone to those expected during the formation of pallasite meteorites and lunar rocks. Because of the cosmochemical significance of the merrillite-keplerite series and by analogy to plagioclases, the Na-number measure, 100 ×Na/(Na+Ca) (apfu), is herein proposed for the characterization of solid solutions between merrillite and keplerite. The merrillite end-member, Ca 9 NaMg(PO 4 ) 7 , has the Na-number = 10, whereas keplerite, Ca 9 (Ca 0.5 ◻ 0.5 )Mg(PO 4 ) 7 , has Na-number = 0. Keplerite (IMA 2019-108) is named in honor of Johannes Kepler (1571–1630), a prominent German naturalist, for his contributions to astronomy and crystallography.

The present investigation reports the equation of state, thermodynamic, and thermoelastic properties of type AB carbonated apatite [CAp-AB, Ca 10 (CO 3 ) B (PO 4 ) 5 (CO 3 ) A , space group P 1], as obtained from density functional theory simulations and the quasi-harmonic approximation. The static (0 K) third-order Birch-Murnaghan equation of state resulted in the parameters K 0 = 104.3(8) GPa, K ′ = 4.3(1), and V 0 = 517.9(2) Å 3 , whereas at room temperature (300 K) they were K T = 101.98 GPa, K ′ = 4.12, and V 0 = 524.486 GPa. Thermodynamics and thermoelasticity were calculated in the temperature range 0–800 K and between 0 and 30 GPa. Furthermore, the dependence of the infrared/Raman spectra of type-AB carbonated apatite with pressure is also reported, which could be useful for researchers interested in vibrational spectroscopy. The theoretical results corroborate the few experimental ones on a similar type-AB carbonated hydroxylapatite and provide further details over wide pressure and temperature ranges on the elastic, thermodynamic, and infrared/Raman properties of this important mineral found in both geological and biological environments.

We conducted a series of high-temperature experiments where single crystals of CaTiO 3 were embedded in PbTiO 3 powder for durations of 4 to 502 h at temperatures between 753 and 1207 °C. Combined with results from a previous study (Beyer et al. 2019), these experiments allow us to explore the influence of chemical potential gradients on the mechanisms of incorporation of Pb in CaTiO 3 . Unlike in the previous study where Pb diffused into CaTiO 3 , here we find that the rims of the CaTiO 3 crystals recrystallize to form a polycrystalline aggregate of [Pb x Ca (1–x) ]TiO 3 solid solutions. The width of the recrystallized front increases with run duration, and the contact to the single crystal becomes progressively wavy. The concentration of Pb decreases within the recrystallized front toward the interior of the single crystal, and the newly formed crystals are of different chemical compositions and orientations and are themselves chemically zoned. There is a discontinuous jump in Pb-concentration at the contact of the recrystallized front with the single crystal (termed “the migrating interface”). The development of chemical concentration gradients, combined with the fact that the width of the front grows as the square-root of time indicates a role of diffusion in the process; the formation of new crystals with different composition and no orientation relation to the precursor, and the jump in concentration at the boundary between the newly formed crystals and the single crystal indicates a dissolution-precipitation type process. Thus, this is a novel mechanism where diffusion, as well as dissolution-precipitation (in the sense that the structure of the single crystal is destroyed and replaced by new crystals), occurs simultaneously in a coupled manner and neither is rate-determining. The observations in this experimental study provide several insights into the mechanisms of chemical transformation in such non-metallic materials: (1) chemical differences can trigger mechanical deformation, which in turn can control chemical fluxes; (2) newly formed crystals, even at the high temperatures of the experiments, evolve continuously in chemistry and are not of an equilibrium composition; (3) the activation energy of the overall process (~70 kJ/mol) is lower than that for diffusion and provides a more effective means of chemical transformation, even though diffusion plays a central role in the process; and (4) it underscores the role of surface/interface free energy in the evolution of the transformation process. These results have important consequences for the reading of the petrological and geochemical signatures of the rock record—notably, in addition to knowing when a phase becomes chemically stable, it is also important to know when a particular crystal of the phase begins to exist. Some possible implications for thermobarometry, isotopic dating, and geospeedometry/ diffusion chronometry are discussed.

The transport properties of liquid iron alloys at high pressure ( P ) and temperature ( T ) are essential for understanding the formation, composition, and evolution of planetary cores. Light alloying elements (e.g., Si, O, S, C, N, H) in liquid iron are particularly relevant due to the density deficit of Earth’s core, yet high P-T experimental diffusion studies involving such alloys remain scarce, with large uncertainties on the P and T dependence required for extrapolation to core conditions. In this study, we measured the chemical diffusion of carbon in liquid iron over a P-T range of 3–15 GPa and 1700–2450 K using a multi-anvil apparatus. Diffusion couples consisting of pure Fe and Fe-2.5 wt%C cylinders were placed end-to-end in an MgO capsule in a vertical orientation. Carbon concentration profiles were measured by electron microprobe and modeled numerically to correct for non-isothermal diffusion that occurred prior to reaching the peak temperature. Carbon diffusion coefficients range from 6 × 10 −9 m 2 ·s −1 to 2 × 10 −8 m 2 ·s −1 , with global Arrhenian fit parameters D 0 = 1.4 ± 0.5 × 10 −7 m 2 ·s −1 , Δ E = 43 ± 6 kJ/mol, and Δ V = −0.06 ± 0.19 cm 3 ·mol −1 . A negligible P effect is consistent with previous studies of oxygen diffusion in liquid iron and high- T calculations but differs from larger Δ V values previously reported from carbon self-diffusion experiments for liquid Fe 3 C and simulations for an Fe-Ni–C alloy. Carbon diffusion coefficients determined here are approximately three times faster than those reported from Fe-Ni-C liquid simulations, which highlights the potential significance of compositional effects on mass transport properties of liquid iron alloys and the need for expanding the P-T experimental diffusion data set currently available in the literature to more complex and geologically relevant compositions.

Studies have shown the electron shuttling role of humic substances (HS) in enhancing microbial reduction of solid-phase Fe(III), but it is unknown if native HS can reduce structural Fe(III) in clays and how their chemical properties afect this process and secondary mineralization. The objective of this study was to evaluate the role of natural HS, Leonardite humic acid (LHA), and Pahokee Peat humic acid (PPHA) in reducing structural Fe(III) in nontronite with or without Shewanella putrefaciens . The extent of Fe(III) reduction was determined with a wet chemical method. Electrochemical methods, spectroscopy, and mass spectrometry were used to determine the changes of HS electrochemical and molecular composition after bioreduction. X‑ray difraction and electron microscopy were used to observe mineralogical transformations. The results showed that natural HS not only served as an electron donor to abiotically reduce Fe(III) in nontronite but also served as an electron shuttle to enhance Fe(III) bioreduction by S. putrefaciens . In the presence of CN32 cells, both the rate and extent of Fe(III) reduction significantly increased. Between the two HS, PPHA was more efective. The final bioreduction extents were 12.2 and 17.8% with LHA and PPHA, respectively, in bicarbonate bufer. Interestingly, when CN32 cells were present, LHA and PPHA donated more electrons to NAu-2, suggesting that CN32 cells were able to make additional electrons of LHA and PPHA available to reduce structural Fe(III). Although LHA reduced less Fe(III), it induced more extensive mineral transformation. In contrast, PPHA reduced more Fe(III) but did not induce any mineralogical change. These contrasting behaviors between the two humic acids are ascribed to their diferences in electron-donating capacity, reactive functional group distribution, and metal complexation capacity. A unique set of secondary minerals, including talc, illite, silica, albite, ilmenite, and ferrihydrite formed as a result of reduction. The results highlight the importance of coupled C and Fe biogeochemical transformations and have implications for nutrient cycling and contaminant migration in the environment.

To evaluate the mechanisms driving nanoscale trace element mobility in radiation-damaged zircon, we analyzed two well-characterized Archean zircons from the Kaapvaal Craton (southern Africa): one zircon remained untreated and the other was experimentally heated in the laboratory at 1450 °C for 24 h. Atom probe tomography (APT) of the untreated zircon reveals homogeneously distributed trace elements. In contrast, APT of the experimentally heated zircon shows that Y, Mg, Al, and Pb+Yb segregate to a set of two morphologically and crystallographically distinct cluster populations that range from 5 nm tori to 25 nm toroidal polyhedra, which are confirmed to be dislocation loops by transmission electron microscopy (TEM). The dislocation loops lie in {100} and {001} planes; the edges are aligned with <100>, <101>, and <001>. The largest loops (up to 25 nm diameter) are located in {100} and characterized by high concentrations of Mg and Al, which are aligned with <001>. The 207 Pb/ 206 Pb measured from Pb atoms located within all of the loops (0.264 ± 0.025; 1σ) is consistent with present-day segregation and confirms that the dislocation loops formed during our experimental treatment. These experimentally induced loops are similar to clusters observed in zircon afected by natural geologic processes. We interpret that diferences in cluster distribution, density, and composition between experimentally heated and geologically afected zircon are a function of the radiation dose, the pressure-temperature-time history, and the original composition of the zircon. These findings provide a framework for interpreting the significance of clustered trace elements and their isotopic characteristics in zircon. Our findings also suggest that the processes driving cluster formation in zircon can be replicated under laboratory conditions over human timescales, which may have practical implications for the mineralogical entrapment of significant nuclear elements.

Tin isotope geochemistry of cassiterite may allow for reconstructing the fluid evolution of tin ore deposits. Here, we present cathodoluminescence (CL) imaging, trace element, and in situ Sn isotope compositions of two cassiterite crystals from an early and a relatively late stage of ore formation of the Xiling vein-style Sn deposit, southeastern China, by femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS). Our results show that the early-stage cassiterite from a high-temperature feldspar-stable hydrothermal environment has core, mantle, and rim zones with a systematic decrease in δ 124/117 Sn 3161A (relative to the Sn standard NIST 3161 A) from +0.38 ± 0.06‰ in the crystal core to –0.12 ± 0.06‰ (2 SE) in the mantle zone. This isotopic evolution, also paralleled by a decrease in Ta content by two orders of magnitude, suggests a fluid batch evolving toward isotopically lighter Sn. The very rim zone of this crystal has an intermediate tin isotope composition at about +0.05‰ δ 124/117 Sn 3161A , combined with elevated Ta, suggestive of a second fluid batch. The late-stage cassiterite crystal from a muscovite-stable hydrothermal environment has a core with an evolved Sn isotope composition at about –0.15‰ δ 124/117 Sn 3161A combined with low Ta, and a rim with heavier Sn isotope compositions up to +0.30 ± 0.08‰ δ 124/117 Sn 3161A and higher Ta contents. As for the early-stage crystal, two diferent fluid batches must be involved in the formation of this crystal. Our pilot study highlights the advantage of spatially resolved analysis compared to conventional, solution Sn-isotope analysis of bulk cassiterite crystals. The Sn isotope variations at the microscale reveal the complexity of cassiterite crystal growth by a combination of closed- and open-system fluid evolution and isotope fractionation.

Texturally complex minerals can provide critical information on dynamic hydrothermal processes. This study combines cathodoluminescence (CL), laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS), and high-resolution femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (fs–LA–MC–ICP–MS) analyses to document textures, in situ Sr-Nd isotope systematics, and trace element compositions of texturally complex scheelite from the Yangjiashan W deposit, South China. The major motivation for this contribution was to reveal the correlation between CL response, textures, and trace element concentrations; document the origin of various REE fractionation patterns; and characterize grain-scale in situ variability of Sr-Nd isotopes of scheelite. Five sub-types of scheelite from both stages, including Sch1 and Sch2 from Stage 1, and Sch3 to Sch5 from Stage 2, are identified. CL images feature complex oscillatory, patchy, and evidence for coupled dissolution-reprecipitation reaction. These scheelites precipitated from reduced fluids and are close to end-member in composition, with Mo concentrations below 46 ppm. Concentrations of other elements vary, e. g., Sr (36–1025 ppm), Nd (8–351 ppm), and Na (7–300 ppm). LA–ICP–MS element maps reveal a large variability in REE concentrations among oscillatory zones and no consistent behavior between REE, Sr and Mo concentration, and CL intensity. Four distinct chondrite-normalized REE fractionation patterns are recognized: LREE-enriched, MREE-enriched, HREE-enriched, and flat patterns. Complex Eu anomalies (δEu = 0.2 to 20.7) are recognized among the five sub-types and are commonly observed within individual grains. Fluid compositions, different substitution mechanisms (i.e., Ca 2+ + W 6+ = REE 3+ + Nb 5+ , and 2Ca 2+ = REE 3+ + Na + , 3Ca 2+ = 2REE 3+ + □Ca, where □Ca is a Ca-site vacancy), primary-secondary processes (i.e., oscillatory and dissolution-reprecipitation, respectively), all contribute to the variation in REE fractionation patterns. Local fluctuation in fluid pH is responsible for the complex Eu anomalies. In situ Sr and Nd isotope signatures for the five sub-types of scheelite show relatively large ranges, i.e., the initial 87 Sr/ 86 Sr ratios range from 0.71336 to 0.72617, and the initial εNd values ranging from –24.9 to –7.7, suggesting a source derived from a mixture of magmatic-hydrothermal fluids and the Neoproterozoic slate. Decreasing 87 Sr/ 86 Sr ratios from Sch2 to Sch5 record decreasing fluid-rock interaction intensity. Large variation of εNd(t) values (–24.9 to –7.7) of scheelite with oscillatory zoning textures may relate to changes of Sm/Nd ratio of scheelite and contamination from wall rock with inhomogeneous Nd isotope composition. This study highlights the importance of performing coupled LA–ICP–MS mapping and in situ Sr-Nd isotope analyses on sample material that has been characterized in detail at the micrometer scale.

Tellurium-rich (Te) adularia-sericite epithermal Au-Ag deposits are an important current and future source of precious and critical metals. However, the source and evolution of ore-forming fluids in these deposits are masked by traditional bulk analysis of quartz oxygen isotope ratios that homogenize fine-scale textures and growth zones. To advance understanding of the source of Te and precious metals, herein, we use petrographic and cathodoluminescence (CL) images of such textures and growth zones to guide high spatial resolution secondary ion mass spectroscopy (SIMS) oxygen isotope analyses (10 μm spot) and spatially correlated fluid inclusion microthermometric measurements on successive quartz bands in contemporary Te-rich and Te-poor adularia-sericite (-quartz) epithermal Au-Ag vein deposits in northeastern China. The results show that large positive oxygen isotope shifts from –7.1 to +7.7‰ in quartz rims are followed by precipitation of Au-Ag telluride minerals in the Te-rich deposit, whereas small oxygen isotope shifts of only 4‰ (–2.2 to +1.6‰) were detected in quartz associated with Au-Ag minerals in the Te-poor deposits. Moreover, fluid-inclusion homogenization temperatures are higher in comb quartz rims (avg. 266.4 to 277.5 °C) followed by Au-Ag telluride minerals than in previous stages (~250 °C) in the Te-rich deposit. The Te-poor deposit has a consistent temperature (~245 °C) in quartz that pre- and postdates Au-Ag minerals. Together, the coupled increase in oxygen isotope ratios and homogenization temperatures followed by precipitation of Au-Ag tellurides strongly supports that inputs of magmatic fluid containing Au, Ag, and Te into barren meteoric water-dominated flow systems are critical to the formation of Te-rich adularia-sericite epithermal Au-Ag deposits. In contrast, Te-poor adularia-sericite epithermal Au-Ag deposits show little or no oxygen isotope or fluid-inclusion evidence for inputs of magmatic fluid.

Thalliomelane, a new member of the coronadite group (hollandite supergroup), was discovered at Zalas near Kraków in southern Poland (the southern margin of the Kraków-Silesia Monocline) in relics of a preglacial supergene mineralization disseminated in a fault breccia in Middle Jurassic sandy limestone. The mineralization formed at the expense of a sulfide assemblage, which was most likely the source of thallium, related to rejuvenation of Early-Paleozoic fault zones in the Sava phase of the Alpine orogeny. Thalliomelane occurs rarely and exclusively in the form of fibrous and highly porous tiny aggregates <50 μm in size that fill small fractures and voids in the sandy limestone host rock. Microprobe analyses based on 16 O and 8 octahedral cations per formula unit resulted in the mean empirical formula [Tl 0.77(10) Ba 0.21(3) K 0.03(1) Na 0.01(0) Pb 0.01(0) ] Σ1.03(7) [Mn 4 7.15 + (11) Cu 2 0.63 + (4) Co 2 0.08 + (3) Fe 3 0.06 + (3) Ni 2 0.03 + (1) Si 0.03(2) Mg 0.01(1) ] Σ8 [O 15.67(24) (OH) 0.33(24) ], corresponding to the formula Tl(Mn 4 7.5 + Cu 2 0.5 + )O 16 for the thalliomelane end-member. The mineral crystallizes in the tetragonal system, space group I 4/ m , and has unit-cell parameters a = 9.8664(12), c = 2.8721(4) Å, V = 279.59(8) Å 3 , Z = 1. The crystal structure of thalliomelane, measured with 3D electron-diffraction, was refined to an R 1 index of 23.74%. Thalliomelane has the hollandite-type structure. The Mn 4+ cations, substituted by Cu 2+ at an amount of ~0.5 apfu, are octahedrally coordinated by oxygen atoms. Four double chains of edge-sharing (Mn,Cu)-O octahedra share corners with each other to form tunnels along the [001] direction. Tl + cations are located in the tunnels, occupying partially the origin and center of the unit cell. The formation of thalliomelane was most probably connected to the weathering of a sulfide mineral assemblage under semi-arid to arid climate. It resulted in the release of Tl and other components of the mineralization into water under the influence of Cl-, Br-, and I-bearing brines and pore waters from the Carpathian flysch or from sediments of the Carpathian foredeep mobilized by compaction during the Sava phase. Via the interaction of these waters, the primary ores altered mainly into goethite, cuprite, malachite, Mn oxides of the coronadite type, with subordinate Cu sulfates, Pb arsenates, Bi oxy-chlorides, and traces of iodargyrite. This assemblage indicates oxidation at a progressively increasing pH of ~8–10 and Eh of the order of +0.4–0.5 V. In this setting, thalliomelane could have formed from a cryptomelane-type Mn oxide in contact with Tl-bearing aqueous solutions through Tl-for-K exchange over time.

In this issue In this series of New Mineral Names, a thematic approach is used to help provide context for advances and discoveries in mineralogy. Planet Earth is ever-changing, and unique crystals are found in the tiniest of micro-geologic niches. With emerging analytical techniques, the formerly inaccessible becomes accessible. New minerals inspire creative approaches to overcoming chemical and technological challenges and can reveal what the Earth was like billions of years ago. In this issue, we look at recently described minerals that are associated with diamonds, dumps, and fumaroles: crowningshieldite, goldschmidtite, breyite, cardite, grimmite, hrabákite, freitalite, dioskouriite, dobrovolskyite, ferroefremovite, and vasilseverginite.