Volume 107, Issue 8

Kaolinite is an Al-rich phyllosilicate commonly observed on Earth as a product of the chemical weathering of aluminosilicates. It has also been detected on the martian surface by orbital remote sensing observations. While the determination of the geological processes of formation of terrestrial kaolinite (i.e., hydrothermal activity, continental surface weathering, diagenesis) involves the coupling of field observation and multiple laboratory measurements, only geomorphology and associated minerals are generally available to determine their geological origin on Mars. Kaolinite crystallinity depends on many physicochemical parameters reflecting its conditions of crystallization. To determine if the near-infrared (NIR) spectral signature of kaolinite enables estimation of its crystallinity and furthermore if this method can be used to identify the geological processes involved in kaolinite formation, we carried out an in-depth analysis of NIR spectra of reference terrestrial kaolinites that formed in various geological contexts. We calculated second and third derivatives for each spectrum to highlight subtle variations in the spectral properties of kaolinite. This allowed the identification of 27 spectral contributions for the 4500 and 7000 cm −1 Al-OH-related regions of absorption bands. The position shifts and shape variations of these spectral contributions were intimately linked to variations of crystallinity, which was qualitatively estimated using Hinckley and Liétard XRD (dis)order indices. The results obtained show that the NIR signature of kaolinite is influenced by the stacking disorder of layers that has some influence on the vibrations of the interfoliar and inner Al-OH groups. Our study also confirms that: (1) well-ordered kaolinites are not restricted to hydrothermal deposits; (2) kaolinites from a similar sedimentary or pedogenetic context often display contrasting degrees of crystalline order; and (3) poorly ordered kaolinites are more likely to have a sedimentary or pedogenetic origin. Finally, this work highlights that obtaining spectra with sufficient spectral resolution could help to estimate the crystallinity of kaolinite and, in the best cases, its geological origin, both on Earth and Mars, especially with in situ NIR measurements.

We report a first-principles-based thermodynamic investigation of the interplay between cation inversion and twinning in MgAl 2 O 4 spinel (MAS). We examine the atomic-scale structure of (111) twins and characterize the local octahedral and tetrahedral distortions. We observe that the asymmetric nature of polyhedral distortions about the (111) twin plane causes anisotropy in cation inversion energies near the planar fault. The predicted enthalpies and entropies of inversion reveal that in comparison to the Kagome layer, the anti-site occupancies of Al and Mg, i.e., cation inversion, on the mixed-cation-layer near the twin boundary are more favorable and stable in the entire range of temperature of twin stability. Structurally, such a stable inversion is necessitated by the minimization in the polyhedral distortions, especially by the octahedral distortion, which exhibits a reduction of four orders of magnitude relative to the polyhedra with no inversion. The fundamental understanding obtained on the thermodynamics of the twin-cation inversion interplay in conjunction with the kinetics of inversion was used as a basis for developing a thermochronometer for deducing the temperature of twinning in MAS. This work serves as an important steppingstone for experimental characterization of MAS structures within a host of Earth and planetary materials. In the case of the latter, our results enable the use of planar faults, such as twins, as important markers for deducing the physical and chemical landscape that MAS experienced in its evolution and transport within the solar protoplanetary disk.

Growth of reaction rims is mainly controlled by a change in physical parameters such as pressure and temperature, a change in the chemical composition of the system, and/or by the presence of volatiles. In particular, the effect of volatiles other than water on reaction-rim growth remains poorly understood. To accurately model metamorphic and metasomatic processes, a quantification of the efect of volatiles on reaction-rim growth dynamics is necessary but hitherto missing. In this study, reaction rims were experimentally grown in a series of piston-cylinder experiments in the ternary CaO-MgO-SiO 2 system at 1000 °C and 1.5 GPa with 0–10 wt% F for 20 min. In the fluorine-free system, a rim sequence of wollastonite (Wo) | merwinite (Mer) | diopside (Di) | forsterite (Fo) | periclase (Per) formed, complying with the stable phase configuration at water-saturated conditions. As soon as 0.1 wt% F was introduced into the system, humite group minerals (HGMs) and monticellite (Mtc) appeared, resulting in the multilayer rim sequence Wo | Mer | Mtc | Fo + HGMs | Per. In experiments with fluorine concentrations ≥0.5 wt%, cuspidine (Csp) appears in the layer sequence and represents the major fluorine sink. Our data show that the addition of fluorine may stabilize the fluorine-bearing phases cuspidine and HGMs to higher temperatures, which is in agreement with previous studies (Grützner et al. 2017). However, the appearance of the nominally anhydrous minerals (NAMs) monticellite and åkermanite (Ak) at this P-T condition suggests that the addition of fluorine may also afect the stability of nominally fluorine-free minerals. This may be explained by the efect of fluorine on the Gibbs free energies of fluorine-bearing phases, which in turn afects the relative Gibbs free energies and thus the stabilities of all phases. An increase in absolute rim thickness from 11.8(21) to 105.6(22) μm (1σ standard deviations in parentheses) in fluorine free and 10 wt% F experiments, respectively, suggests that fluorine enhances absolute component mobilities and thus results in faster rim growth rates. Additionally, due to the presence of fluorine, a change in relative component mobilities results in microstructural changes such as a phase segregation of diopside and cuspidine at high-fluorine (≥3 wt% F) concentrations. These results not only imply that reaction rims may be used as a tool to infer the amount of fluorine present during metamorphic reactions but also that we need to consider the role of fluorine for a correct interpretation of the P-T - t history of metamorphic and metasomatic rocks.

The Lewisian Complex in northwest Scotland presents a record of the transition from the Neo-Archean to the Paleoproterozoic. However, this record is complicated by a long and varied history after peak metamorphism that has erased and/or partially reset much of the early history of the rocks. Such overprinting is a common feature of Archean granulites and poses a substantial problem when trying to understand the tectonic processes that were active prior to the onset of modern plate tectonics. By combining careful petrography with phase diagram modeling and a range of exchange thermometers we obtain the peak and retrograde temperature history of the Lewisian Complex from a single, well-preserved, representative sample of garnet-bearing mafic granulite. We present the application of high-resolution electron probe microanalysis (HR-EPMA) to characterize sub-micrometer orthopyroxene exsolution lamellae in clinopyroxene. We discuss ways to mitigate issues associated with HR-EPMA including surface contamination, beam drift, standards, and the need to correct for secondary fluorescence effects. The resulting compositions from our HR-EPMA analyses provide an independent measure of the retrograde temperature conditions and can also be used to back-calculate the compositions of clinopyroxene in the peak assemblage. We obtain peak metamorphic conditions for the Lewisian of >11 kbar and >1025 °C, and constrain subsequent metamorphic overprints to 850 °C (Grt-Cpx), 590 °C (Opx-Cpx), and 460 °C (Mag-Ilm). These peak and retrograde temperatures span the range of those found in the literature. Whereas recent phase equilibrium studies assume equilibrium among all preserved high- T minerals, this study considers microstructural and mineral-chemical evidence for corona formation that reflects post-peak decompression with partial equilibration at ~850 °C, as recognized in some earlier studies.

Interphase boundaries are planar defects that separate two different minerals, which in general have different compositions and/or crystalline structures; they may play an important role as a pathway for fluids in rocks and affect their physical properties. To completely characterize interphase boundaries, one needs to define the misorientation between adjacent grains and the orientation of the grain boundary plane. The analysis performed here is limited to the misorientation characterization and the trace of the interphase boundary. Although the determination of possible orientation relationships between the two adjacent phases is routinely performed by selected-area electron diffraction in a transmission electron microscope, this method lacks statistical representativeness. With the advent of techniques like electron backscatter diffraction (EBSD), it is possible to calculate orientation relationships not only in single pairs of crystals of the same phase but in full thin sections and between different minerals. The interphase misorientation is calculated from two orientations of two adjacent crystals of different phases. A set of single misorientations is then used to calculate the misorientation distribution function (MDF), from where it is possible to identify a maximum and its crystallographic interpretation. If we then know the misorientation and the unit-cell parameters of the individual phases, the crystallographic relationships between the different phases can be described with the pairs of parallel crystallographic planes and the pairs of crystallographic directions. In this paper, I present examples of the use of interphase misorientation analysis on the transformation of calcite-aragonite, olivine-antigorite, magnetite-hematite, and on the study of orientation relationships between plagioclase-olivine-ilmenite in mid-ocean ridges gabbros (ODP Hole 735).

Mineral/melt partition coefficients have been widely used to provide insights into magmatic processes. Olivine is one of the most abundant and important minerals in the lunar mantle and mare basalts. Yet, no systematic olivine/melt partitioning data are available for lunar conditions. We report trace element partition data between host mineral olivine and its melt inclusions in lunar basalts. Equilibrium is evaluated using the Fe-Mg exchange coefficient, leading to the choice of melt inclusion-host olivine pairs in lunar basalts 12040, 12009, 15016, 15647, and 74235. Partition coefficients of 21 elements (Li, Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Co, Y, Zr, Nb, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) were measured. Except for Li, V, and Cr, these elements show no significant difference in olivine-melt partitioning compared to the data for terrestrial samples. The partition coefficient of Li between olivine and melt in some lunar basalts with low Mg# (Mg# < 0.75 in olivine, or < ~0.5 in melt) is higher than published data for terrestrial samples, which is attributed to the dependence of D Li on Mg# and the lack of literature D Li data with low Mg#. The partition coefficient of V in lunar basalts is measured to be 0.17 to 0.74, significantly higher than that in terrestrial basalts (0.003 to 0.21), which can be explained by the lower oxygen fugacity in lunar basalts. The significantly higher D V can explain why V is less enriched in evolved lunar basalts than terrestrial basalts. The partition coefficient of Cr between olivine and basalt melt in the Moon is 0.11 to 0.62, which is lower than those in terrestrial settings by a factor of ~2. This is surprising because previous authors showed that Cr partition coefficient is independent of f O2 . A quasi-thermodynamically based model is developed to correlate Cr partition coefficient to olivine and melt composition and f O2 . The lower Cr partition coefficient between olivine and basalt in the Moon can lead to more Cr enrichment in the lunar magma ocean, as well as more Cr enrichment in mantle-derived basalts in the Moon. Hence, even though Cr is typically a compatible element in terrestrial basalts, it is moderately incompatible in primitive lunar basalts, with a similar degree of incompatibility as V based on partition coefficients in this work, as also evidenced by the relatively constant V/Cr ratio of 0.039 ± 0.011 in lunar basalts. The confirmation of constant V/Cr ratio is important for constraining concentrations of Cr (slightly volatile and siderophile) and V (slightly siderophile) in the bulk silicate Moon.

The use of the field emission gun in scanning electron microscopy permits the imaging of sub-micrometer-size features. However, achieving sub-micrometer analytical spatial resolution in electron probe microanalysis (EPMA) requires both reducing the electron beam size and reducing the accelerating voltage to achieve the desired sub-micrometer interaction volume. The resulting quantification of the first-row transition metals at low accelerating voltage, i.e., below 7–8 kV, is problematic as the main characteristic X‑ray lines ( K α) cannot be excited at these conditions. Furthermore, the use of the L α and L β soft X‑ray lines for quantification is complicated by bonding and self-absorption effects resulting in not-yet-determined mass absorption coefficients and hence in the failure of the traditional matrix correction procedure. We propose two methods to circumvent these low-kilovolt (low-kV) analysis limitations: using the non-traditional Fe L ℓ line and using universal calibration curves for the more traditional Fe L α and L β lines. These methods were successfully applied to Fe-sulfide minerals showing accurate quantification results by EPMA at reduced kV, necessary for accurate quantification of sub-micrometer sulfide grains.

The relationship between plutonic and volcanic components of magmatic plumbing systems continues to be a question of intense debate. The Oki-Dōzen Islands, Sea of Japan, preserve outcrops of temporally associated plutonic, hypabyssal, and volcanic rocks. Post-intrusion uplift juxtaposed Miocene syenites in inferred faulted contact with volcanic trachytes that are cut by rhyolite hypabyssal dikes. This provides a window deep into the timing and origins of magma storage architecture and dynamics. Zircon is ubiquitous in all samples; our aim is to determine what its age and composition can reveal about the plutonic-volcanic connection. Here we show magma source characteristics are recorded in zircon Hf isotopes; source composition and assimilation of heterogeneous hydrothermally altered crust in zircon O isotopes; and extensive fractional crystallization in zircon trace elements. Combined with new U-Th-Pb SHRIMP zircon ages, 6.4–5.7 Ma, compositional data show pluton formation was by protracted amalgamation of discrete magma pulses. The rhyolite dike preserves an evolved fraction segregated from these discrete magmas. Synchronous with plutonism was a volcanic eruption of trachyte magma derived from the same source, which may have stalled at a relatively shallow depth prior to eruption. Stalling occurred at least above the amphibole stability zone because amphibole-compatible Sc and Ti were not depleted in the trachyte melt resulting in elevated values of these in volcanic compared to plutonic zircon. Identifying smaller episodic magma pulses in a larger magmatic complex places constraints on potential magma fluxes and eruptible volumes. High-flux, large volume, plume-related ocean island magmatic systems may have extensive vertically distributed multi-stage magmatic reservoirs and subduction-related systems transcrustal magma reservoirs. By contrast, Oki-Dōzen was a low-flux system with incremental pluton growth and small- to moderate-scale eruptions.

For the first time, cathodoluminescence (CL) was used to show oscillatory zoning in perthitic K‑feldspars from the equigranular Toki granite, central Japan. Based on the CL patterns, two types of zoning are identified: single core oscillatory zoning (SCOZ) and multiple core oscillatory zoning (MCOZ). The SCOZ is defined by oscillatory zoning around a single-crystal core within the K‑feldspar crystal, whereas the MCOZ depicts two or more such crystal cores. The crystal cores displayed in CL images reflect the nucleation parts of magmatic K‑feldspar. The existence of MCOZ patterns in K‑feldspars indicates multiple nuclei. CL patterns reveal crystal growth behavior of magmatic K‑feldspar in the equigranular Toki granite. CL intensities are positively correlated with titanium and barium concentrations, indicating that the CL variations depend on two factors: (1) titanium concentration as a CL activator and (2) density of Al-O − -Al structural defects. The analysis of CL images revealed that albite-rich phases in microperthite and patchperthite with low-luminescence intensities cut across the CL bands of the oscillatory zoning, indicating that the oscillatory zoning in the orthoclase-rich host phase of K‑feldspar was not perturbed by the formation of microperthite and patchperthite in the post-crystallization stage. The luminescence intensities of albite-rich phases in patchperthite are lower than those in microperthite, which is due to the diferences in titanium and barium concentrations between them. In the post-crystallization stage, the mass transfer of titanium and barium occurred during the formation of microperthite and patchperthite. Therefore, the diference in the luminescence intensities between microperthite and patchperthite lamellae reflects their diferent formation mechanisms between exsolution coarsening and dissolution-precipitation coarsening. In summary, CL analyses can be used for the evaluation of the nucleation and growth not only of anhedral K‑feldspar crystals in equigranular granite but also of K‑feldspar phenocrysts/megacrysts in porphyritic granite. It can reveal the spatial extent of element partitioning between the melt and crystal, along with that of mass transfer from the melt into crystals during the magma evolution. Moreover, the CL analyses can also be used for the interpretation of K‑feldspar textural development during the post-crystallization stage.

Piston-cylinder assemblies exhibit inhomogeneous pressure distributions and biases compared to the theoretical pressure applied to the hydraulic press because of the thermal and mechanical properties of the assembly components. Whereas these effects can partially be corrected by conventional calibration, systematic quantification of friction values remain very sparse and results vary greatly among previous studies. We performed an experimental study to investigate the behavior of the most common cell assemblies, i.e., talc [Mg 3 Si 4 O 10 (OH) 2 ], NaCl, and BaCO 3 , during piston-cylinder experiments to estimate the effects of pressure, temperature, run duration, assembly size, and assembly materials on friction values. Our study demonstrates that friction decreases with time and also partially depends on temperature but does not depend on pressure. We determined that friction decreases from 24 to 17% as temperature increases from 900 to 1300 °C when using talc cells, indicating a friction decrease of ~2% per 100 °C increase for 24 h experiments. In contrast, friction becomes independent of time above 1300 °C. Moreover, at a fixed temperature of 900 °C, friction decreases from 29% in 6 h runs to 21% in 48 h runs, corresponding to a decrease of friction of 0.2% per hour. Similar results obtained with NaCl cell assemblies suggest that friction is constant within error, from 8% in 9 h runs to 5% in 24 h runs. At 900 °C, possible steady-state friction values are only reached after at least 48 h, indicating that friction should be considered a variable for shorter experiments. We establish that assembly materials (and their associated thermomechanical properties) influence the friction correction more than the dimensions of the assembly parts. Finally, we show that the use of polytetrafluoroethylene film instead of conventional Pb foil does not modify friction but significantly reduces the force required for sample extraction, thus increasing the lifetime of the carbide core, which in turn enhances experimental reproducibility.

Aluminum-rich and Si-poor calcium amphibole [~3.9 Al atoms per formula unit (apfu) and ~5.5 Si apfu for 23 O] occur in the quartz-bearing eclogites from the Donghai area, Sulu ultrahigh-pressure metamorphic belt, eastern China. Most of the aluminous amphibole phases are retrograde products from the exhumation and hydration stage and are texturally divided into a mantle phase around a porphyroblastic garnet and a crack-filling (vein) phase of a garnet. Less aluminous amphibole occurs as symplectite phase with plagioclase after omphacite. The formation process of the aluminous amphibole in the quartz-bearing samples is discussed on the basis of the analytical data by EPMA, FIB-TEM, and EBSD. The mantle amphibole occurs between garnet and symplectite or quartz. A set of plagioclase and aegirinediopside/argirine-hedenbergite thin monomineralic bands forms at the boundary between the mantle amphibole and matrix quartz. However, these monomineralic bands do not occur at the mantle amphibole-symplectite boundary. These textural diferences indicate that the recrystallization of the aluminous amphibole around garnet was controlled by significant local reactions, and the size of equilibrate domains was probably several tens of micrometers or less. The mantle amphibole is composed of inner (garnet-side) and outer (matrix-side) zones. The inner zone is compositionally homogeneous, and its atomic Al/Si value is ~0.63–0.66 and similar to that of garnet. Atomic Ca/Si value in the inner zone is also almost uniform and is generally identical to that of garnet. The outer zone exhibits a monotonic decrease in the Al/Si and Ca/Si values outward, and its composition at the outermost margin is similar to that of the symplectitic amphibole. The crack-filling amphibole has a composition similar to the inner zone of the mantle amphibole. The CPO pattern of the crack-filling amphibole is diferent from that of the adjacent mantle amphibole, showing that the crack-filling amphibole is cut by the mantle amphibole. The textural relationship between the mantle and crack-filling amphibole phases and their compositional characteristics imply that: (1) the mantle type is a slightly later stage product than the crack-filling type, and (2) the boundary between the inner and outer zones of the mantle aluminous amphibole probably corresponds to the initial surface of the porphyroblastic garnet. The inner zone is considered to have grown inward by simple substitution of garnet, using the tetrahedral and octahedral cations of the garnet as the basic framework. On the other hand, most of the outer zone of the mantle-type amphibole grew outward in the matrix from the initial surface of the garnet porphyroblast. The mantle amphibole shows a CPO similar to that of amphibole in the adjacent symplectite domain, suggesting that these two types of amphibole formed almost simultaneously, sharing crystallographic orientation with each other. The formation of crack-filling aluminous amphibole was probably promoted by the hydraulic microfracturing process at an early stage of exhumation and hydration. The mantle and symplectitic amphibole phases formation was promoted by the subsequent infiltration of metamorphic fluid. The aluminous amphibole in the SiO 2 phase-bearing eclogites probably recrystallized with the formation of a localized SiO 2 -undersaturated reaction domain because of rapid exhumation and subsequent rapid cooling of the Sulu UHP metamorphic belt.

Southeastern (SE) Yunnan is a major Sn polymetallic province of China, with the Dulong large Sn-Zn polymetallic deposit (in the Laojunshan orefield) being one of the most representative deposits. Our recent work had first identified helvine- group minerals in this deposit. These minerals mainly occur in massive sphalerite ores, and coexist with sphalerite, pyrrhotite, biotite, talc, cassiterite, and fluorite. Raman spectroscopic, X‑ray difraction (XRD), scanning electron microscopic (SEM), and electron probe microanalysis (EPMA) analyses indicate that these helvine-group minerals are oscillatory-zoned helvine-danalite. Both the helvine and danalite zones are mixed with varying proportion of the other helvine-group end-member, and our studies indicate that the oscillatory zoning was formed mainly by periodic fluctuations of the fluid physicochemical conditions (notably f S2 and f O2 ), but less related to the variation of the fluid Mn, Fe, and Zn contents. The helvine zone was likely formed in a higher f S2 but lower f O2 environment than the danalite zone. In this study, we present the first LA-ICP-MS in situ trace element data for the helvine-danalite minerals from Dulong, and the results indicate that the helvine has considerably high contents and a wide range of trace elements. The helvine is rich in Ca, Al, Sc, and Y, while the danalite is rich in Sn and P (reaching thousands of parts per million). Such trace element enrichments are likely controlled by their respective ionic size and chalcophile behavior. Meanwhile, the f O2 and f S2 conditions during the zoning formation may have also influenced the trace element distributions: trace elements may have mainly entered the helvine-group minerals by substituting into the M-sites in M 4 [BeSiO 4 ] 3 S, for instance Al, Sc, and Y substitute for Mn, and Sn and Mg for Fe and Zn. It is noteworthy that the helvine and danalite zones are all HREE-enriched and have distinct negative Eu anomalies. This may be related to the high fluid F-Y-P contents during the mineral formation. High-F-Y fluids can readily incorporate HREEs into helvine-group minerals, and phosphates incorporate HREEs more readily in alkali fluids. Europium occurs as Eu 2+ in the fluid, causing the negative Eu anomalies observed. We have also identified grains of cassiterite in the helvine-group minerals and its coexisting sphalerite. U-Pb dating on these cassiterite grains yielded 86.5 ± 1.6 Ma, coeval with the reported sulfide mineralization age. This indicates that both the Be and Sn-Zn polymetallic mineralization occurred in the Cretaceous, and may have been products of the Late Yanshanian Laojunshan magmatic-hydrothermal activity. Considering the close relations with many W(-Be) deposits nearby (e.g., Nanyangtian, Saxi, and Maka), the Laojunshan orefield may also have substantial Be mineralization potential.

Seafloor hydrothermal chimneys from back-arc basins are important hosts for metals such as Cu, Zn, Pb, Ag, and Au. Although the general growth history of chimneys has been well documented, recent studies have revealed that the fine-scale mineralogy can be highly complex and reflects variable physicochemical conditions of formation. This study utilized a novel combination of scanning electron microscopy (SEM)-based electron backscattered difraction (EBSD) and synchrotron X‑ray fluorescence microscopy (SXFM) to uncover the detailed growth processes of multiple chalcopyrite-lined conduits within a modern chalcopyrite-sphalerite chimney from Manus Basin and to assess the controls on native gold precipitation. On the basis of previous studies, the chimney conduit was thought to develop from an initial sulfate-dominated wall, which was subsequently dissolved and replaced by sphalerite and chalcopyrite during gradual mixing of hydrothermal fluids and seawater. During this process, sphalerite was epitaxially overgrown by chalcopyrite. Accretionary growth of chalcopyrite onto this early formed substrate thickened the chimney walls by bi-directional growth inward and outward from the original tube wall, also enclosing the outgrown pyrite cluster. A group of similar conduits with slightly diferent mineral assemblages continued to form in the vicinity of the main conduit during the further fluid mixing process. Four types of distinct native gold-sulfide/ sulfosalt associations were developed during the varying mixing of hydrothermal fluids and seawater. Previously unobserved chains of gold nanoparticles occur at the boundary of early sphalerite and chalcopyrite, distinct from gold observed in massive sphalerite as identified in other studies. These observations provide baseline data in a well-preserved modern system for studies of enrichment mechanisms of native gold in hydrothermal chimneys. Furthermore, native gold is relatively rarely observed in chalcopyrite-lined conduit walls. Our observations imply that: (1) native gold is closely associated with various sulfides/sulfosalts in chalcopyrite-lined conduit walls rather than limited to the association with tennantite, Bi-rich minerals, and bornite as reported previously; and (2) the broad spectrum of gold occurrence in chalcopyrite-line conduits is likely to be determined by the various mixing process between hot hydrothermal fluids with surrounding fluids or seawater. Quantitative modeling of fluid mixing processes is recommended in the future to probe the precise gold deposition stages to eficiently locate gold in modern hydrothermal chimneys.

The new apatite-group mineral pliniusite, ideally Ca 5 (VO 4 ) 3 F, was found in fumarole deposits at the Tolbachik volcano, Kamchatka, Russia, and in a pyrometamorphic rock of the Hatrurim Complex, Israel. Pliniusite, together with fluorapatite and svabite, forms a novel and almost continuous ternary solid-solution system characterized by wide variations of T 5+ = P, As, and V. In paleo-fumarolic deposits at Mountain 1004 (Tolbachik), members of this system, including the holotype pliniusite, are associated with hematite, tenorite, diopside, andradite, kainotropite, baryte and supergene volborthite, brochantite, gypsum and opal. In sublimates of the active Arsenatnaya fumarole (Tolbachik), pliniusite–svabite–fluorapatite minerals coexist with anhydrite, diopside, hematite, berzeliite, schäferite, calciojohillerite, forsterite, enstatite, magnesioferrite, ludwigite, rhabdoborite-group fluoroborates, powellite, baryte, udinaite, arsenudinaite, paraberzeliite, and spinel. At Nahal Morag, Negev Desert, Israel, the pliniusite cotype and V-bearing fluorapatite occur in schorlomite-gehlenite paralava with rankinite, walstromite, zadovite-aradite series minerals, magnesioferrite, hematite, khesinite, barioferrite, perovskite, gurimite, baryte, tenorite, delafossite, wollastonite, and cuspidine. Pliniusite forms hexagonal prismatic crystals up to 0.3 × 0.1 mm and open-work aggregates up to 2 mm across (Mountain 1004) or grains up to 0.02 mm (Nahal Morag and Arsenatnaya fumarole). Pliniusite is transparent to semitransparent, colorless or whitish, with a vitreous luster. The calculated density is 3.402 g/cm −3 . Pliniusite is optically uniaxial (–), ω = 1.763(5), ε = 1.738(5). The empirical formulas of pliniusite type specimens calculated based on 13 anions (O+F+Cl) per formula unit are (Ca 4.87 Na 0.06 Sr 0.03 Fe 0.02 ) Σ4.98 (V 1.69 As 0.66 P 0.45 S 0.12 Si 0.09 ) Σ3.01 O 11.97 F 1.03 (Mountain 1004) and (Ca 4.81 Sr 0.12 Ba 0.08 Na 0.05 ) Σ5.06 (V 2.64 P 0.27 S 0.07 Si 0.03 ) Σ3.01 O 12.15 F 0.51 Cl 0.34 (Nahal Morag). Pliniusite has a hexagonal structure with space group P 63/ m , a = b = 9.5777(7), c = 6.9659(5) Å, V = 553.39(7) Å 3 , and Z = 2. The structure was solved using single-crystal (holotype) X‑ray difraction, R = 0.0254. The mineral was named in honor of the famous Roman naturalist Pliny the Elder, born Gaius Plinius Secundus (AD 23–79). It is suggested that the combination of high temperature, low pressure, and high oxygen fugacity favors the incorporation of V 5+ into calcium apatite-type compounds, leading to the formation of fluorovanadates.

Heamanite-(Ce) (IMA 2020-001), ideally (K 0.5 Ce 0.5 )TiO 3 , is a new perovskite-group mineral found as an inclusion in a diamond from the Gahcho Kué mine in the Northwest Territories, Canada. It occurs as brown, translucent single crystals with an average maximum dimension of ~80 μm, associated with rutile and calcite. The luster is adamantine, and the fracture conchoidal. Heamanite-(Ce) is the K-analog of loparite-(Ce), ideally (NaCe)Ti 2 O 6 . The Mohs hardness is estimated to be 5½ by comparison to loparite-(Ce), and the calculated density is 4.73(1) g/cm 3 . Electron microprobe wavelength-dispersive spectrometric analysis (average of 34 points) yielded: CaO 10.70, K 2 O 7.38, Na 2 O 0.16, Ce 2 O 3 13.77, La 2 O 3 8.22, Pr 2 O 3 0.84, Nd 2 O 3 1.59, SrO 6.69, BaO 2.96, ThO 2 0.36, PbO 0.15, TiO 2 45.77, Cr 2 O 3 0.32, Al 2 O 3 0.10, Fe 2 O 3 0.09, Nb 2 O 5 0.87, UO 3 0.01, total 99.98 wt%. The empirical formula, based on 3 O atoms, is: [(K 0.268 Na 0.009 ) Σ0.277 (Ce 0.143 La 0.086 Pr 0.009 Nd 0.016 ) Σ0.254 (Ca 0.326 Sr 0.110 Ba 0.033 Pb 0.001 ) Σ0.470 Th 0.002 ] Σ1.003 (Ti 0.979 Nb 0.011 Cr 0.007 Al 0.003 Fe 0.002 ) Σ1.002 O 3 . The Goldschmidt tolerance factor for this formula is 1.003. Heamanite-(Ce) is cubic, space group Pm 3 m , with unit-cell parameter a = 3.9129(9) Å, and volume V = 59.91(4) Å 3 (Z = 1). The crystal structure was solved using single-crystal X‑ray diffraction data and refined to R 1 ( F ) = 2.61%. Heamanite-(Ce) has the aristotypic perovskite structure and adopts the same structure as isolueshite and tausonite. The six strongest diffraction lines are [ d obs in angstroms ( I in percentages) ( hkl )]: 2.764 (100) (110), 1.954 (41) (200), 1.596 (36) (211), 1.045 (16) (321), 1.236 (13) (310), and 1.382 (10) (220). The Raman spectrum of heamanite-(Ce) shows two broad bands at 560 and 787 cm −1 , with no bands observed above 1000 cm −1 . Heamanite-(Ce) is named after Larry Heaman, a renowned scientist in the field of radiometric dating applied to diamond-bearing kimberlites, mantle-derived eclogites, and lamprophyre dikes. The dominant REE should appear as a Levinson suffix, hence heamanite-(Ce).

Short-range-ordered Fe(III) minerals such as ferrihydrite (Fh) are ubiquitous in the environment, are key players in biogeochemical cycling, and sorb trace elements and nutrients. As such, it is important to be able to identify the presence of such minerals in natural samples. Fh is commonly observed to be X‑ray amorphous and cannot be easily analyzed using X‑ray diffraction, meaning that spectroscopic methods such as X‑ray absorption or 57 Fe Mössbauer spectroscopy (MBS) are necessary for accurate identification and quantification. Despite decades of research into Fh using MBS, there is a discrepancy in the literature about the exact parameters applicable to the mineral when measured at liquid helium temperature. Fh is frequently fitted with either one, two, or three hyperfine sextets with little interpretation applied to the meaning of each, which is problematic as a one sextet model does not account for the asymmetric lineshape frequently observed for Fh. Here, we address inconsistencies in the fitting of Fh and provide a more standardized approach to its identification by MBS. We present a systematic comparison of diferent fitting methods, notably based on Lorentzian and Voigt functions. We suggest that the most suitable approach to fitting pure Fh at liquid helium temperature is with two sextets (A and B) fitted using an extended Voigt-based function with the ability to apply probability distributions to each hyperfine parameter. 2-line Fh: A (δ = 0.49 mm/s; ε = 0.00 mm/s; B hf = 50.1 T) and B (δ = 0.42 mm/s; ε = –0.01 mm/s; B hf = 46.8 T) 6-line Fh: A (δ = 0.50 mm/s; ε = –0.03 mm/s; B hf = 50.2 T) and B (δ = 0.40 mm/s; ε = –0.05 mm/s; B hf = 47.1 T). We interpret the two sextets to be due to either diferences in the coordination environment of iron, i.e., in tetrahedral or octahedral sites, the presence of a disordered surface phase, or a combination of both. We hope that provoking a discussion on the use of MBS for Fh will help develop a greater understanding of this mineral, and other short-range ordered iron minerals, which are so important in environmental processes.

Merrillite, ideally Ca 18 Na 2 Mg 2 (PO 4 ) 14 (Dana No: 38.03.04.04; Strunz No: 08.AC.45), an analog to synthetic tricalcium phosphate β-Ca 3 (PO 4 ) 2 , was identified as an inclusion in lower-mantle diamonds from the Rio Soriso area, Brazil. It was associated with former bridgmanite, CaSi- and CaTi-perovskites, and ferropericlase. This is the first report of merrillite in a terrestrial environment; previously, it was known only in meteorites and lunar rocks. The compositions of merrillite vary in different localities; the Rio Soriso sample was enriched in SO 3 (2.03 wt%). Merrillite from lower-mantle diamonds may be a retrograde phase of the tuite [γ-Ca 3 (PO 4 ) 2 ]. Owing to their crystal structures, both merrillite and tuite may be important potential hosts for rare earth elements (REE) and large ion lithophile elements (LILE), including Sr and Ba, in the deep Earth. The find of merrillite suggests a larger variety of mineral species in the lower mantle than previously assumed.

In this issue of New Mineral Names, a thematic approach is used to help provide context for advances and discoveries in mineralogy. There have been many new minerals described within the last year that have important H 2 O-OH groups within the crystal structure and/or have been formed by hydrothermal processes. Here we investigate the newly discovered hydrous minerals: taniajacoite, strontioruizite, flaggite, steudelite, whiteite-(MnMnMn), zolotarevite, garpenbergite, dobšináite, galeaclolusite, relianceite-(K), and hydroplumboelsmoreite.