Volume 102, Issue 4

The formation of kidney stones is a significant human health problem. Calcium minerals are involved in a majority of these stones. Despite much research, the processes involved in stone formation remain poorly understood and, hence, reliable procedures for preventing their formation have yet to be developed. However, recent advances point to some key steps in mineral formation and transformation involving calcium phosphates, which can help to illuminate these issues. A computer model has been developed to express the current status of literature data succinctly and to illustrate that computer modeling is a powerful tool for calculating mineral solubilities and for providing insight into the processes involved. Determining the nature of the initial solid phase of calcium phosphate formed is evidently important.

Luogufengite, Al-bearing ε-Fe 2 O 3 , is a new member of Fe 2 O 3 polymorphs discovered in late Pleistocene basaltic scoria from the Menan Volcanic Complex nearby Rexburg, Idaho. It is an oxidation product of Fe-bearing basaltic glass at high temperature and is associated with maghemite and hematite. Luogufengite is an euhedral or semi-euhedral nano-mineral with its crystal size ranging from ~20 to ~120 nm. The mineral has a space group of Pna 2 1 ; its unit-cell parameters refined from synchrotron X-ray powder diffraction pattern are a = 5.0647(3), b = 8.7131(6), c = 9.3842(5) Å, and Z = 4 (calculated density = 4.905 g/cm 3 ) with the doubled hexagonal (ABAC) packing of oxygen atoms. The eight strongest lines of the measured X-ray diffraction pattern [d(Å)( I )( hkl )] are: 3.197(27.3)(022); 2.945(29.1) (013); 2.708(100)(122); 2.437(35.8)(131); 1.716(24.4)(204); 1.507(40.7)(135); and 1.458(37.2)(330). The empirical formula is Fe 1.71 Al 0.24 Mg 0.02 Ti 0.03 O 3 . The crystals display (110) twins with twin boundaries of (110), (100), and (130) due to their pseudo-hexagonal symmetry. Luogufengite is an important mineral that records paleomagnetism of volcanic rocks because of its large magnetic coercivity. This unique magnetic property of the mineral may explain the observed unusually high-remanent magnetization in some igneous and metamorphic rocks and even martian rocks with high-remanent magnetization. Some intergrowths of magnetite with ilmenite exsolution lamellae or hematite with magnetite lamellar precipitates have luogufengite-like 2D crystalline characteristics with the doubled hexagonal packing at the interface between cubic and rhombohedral structures. Luogufengite-like nano-domains at the magnetite/hematite interfaces might be responsible for the large coercive field of lodestones that are partially oxidized magnetite with hematite micro-precipitates.

The substitution of F, OH, and Cl in apatite has recently gained increased attention due to the complex nature of incorporation of these three constituents and the implications of apatite column anion chemistry, such as apatite’s contribution to the water budget of the Moon and Mars and the use of apatite anion chemistry as an indicator of halogen and water activities. The solid solutions among F, OH, and Cl are complex because the end-member atomic arrangements cannot fully explain the ternary and binary substitutions of these constituents due to differing atomic radii and the resulting steric constraints in the structure. Three structural variations have recently been reported for the OH-Cl binary solid solution in synthetic samples. This study elucidates column anion arrangements in a chemically zoned ternary apatite from Kurokura, Japan. The structures of the compositionally different core and rim were solved (R1 = 0.0158 and R1 = 0.0143, respectively) in space group P 6 3 / m using single-crystal X-ray diffraction data. The chemistry of these apatites was analyzed using electron microprobe analysis and crystal structure refinement. The core of the Kurokura crystal is a naturally occurring example of the OH ≈ Cl apatite structural variation in a ternary chlorapatite, with four column anion sites (one for F, two for Cl and one for both OH and Cl). The rim exhibits a previously unseen apatite structural variation in a ternary OH-rich fluorapatite (with only a trace Cl component) with three column anion sites (one each for F, OH, and Cl). Both structural variations show a splitting of the Ca2 site that enables reasonable column anion bond distances with Ca2 atoms. A sequence of anions that provides reasonable anion-anion distances while simultaneously enabling reversal of the anion sites relative to the mirror planes at z = ¼ and z = ¾ exists for both structure variations. This study demonstrates the structural complexity of natural ternary apatites, and that a structural variety of OH-Cl apatite occurs over a wider range of chemistry than initially anticipated. The results have implications regarding the poorly understood (and potentially complex) crystallization history of apatite from Kurokura, Japan.

Three Mn-Fe-rich fluorapatite types have been found in the highly evolved peraluminous and perphosphorous granites of the Belvís pluton. One of these apatite types includes abundant graphite microinclusions, suggestive of a magmatic origin for the graphite. The Belvís pluton is a reversely zoned massif composed by four highly fractionated granite units, showing a varied accessory phosphate phases: U-rich monazite, U-rich xenotime, U-rich fluorapatite, and late eosphorite-childrenite. The strong peraluminous character of the granites determines an earlier monazite and xenotime crystallization, so the three types of fluorapatite record late stages of phosphate crystallization. The earlier type 1 apatite is mostly euhedral, small and clear; type 2 apatite is dusty, large (<2800 μm) and mostly anhedral, with strong interlobates interfaces with the main granite minerals, more abundant in the less fractionated units and absent in the most evolved unit; type 3 is subeuhedral to anhedral, shows feathery aggregate texture, and only appears in the most evolved unit. Apatite composition was acquired by electron microprobe analyses, laser ablation inductively coupled plasma-mass spectrometry and electron energy loss spectroscopy. Type 1 and type 2 apatite display similar broad compositional ranges showing high MnO (up to 4.30 wt%) and FeO (up to 2.88 wt%) contents, without traces of carbon in apatite structure. Type 2 differs from type 1 by having slightly higher LREE and Sr contents. REE spectra also differ, with type 1 displaying both variable LREE slope and negative Eu anomaly, whereas type 2 shows constant LREE slope and higher negative Eu anomaly, although both display similar HREE slope. Type 3 apatite displays higher FeO contents (up to 5.09 wt%), positively correlated with higher Cl-Na-Li-Be-B-Zn contents and extremely low Y-REE contents when compared to the other apatite types. Cation substitution indicates that part of the Fe content is as Fe 3+ . Graphite has been found exclusively as abundant microinclusions in type 2 apatite, parallel or randomly distributed, and heterogeneously grouped in clusters within the crystals. High-resolution electronic images show that graphite occurs with unusual habits: filaments of stacked hexagonal flakes up to 15 μm length and up to 0.5 μm width. Textural and chemical features suggest a highly crystallized melt, which favor compartmentalizing in compositional microdomains where the apatite types would have crystallized. The cocrystallization of type 2 apatite and graphite suggests a C-F-P-rich melt, sufficiently saturated to acquire an immiscible character with the highly evolved silicate melt in late-magmatic stages. As type 2 differs from type 1 apatite by higher LREE and Sr contents, we interpret that fluxing components were favorably concentrated in those residual less-depleted LREE-Sr fraction melts, once monazite and zircon (and xenotime) would have crystallized. Type 3 apatite records a change in the ultimate melt stage: an increase of the oxygen fugacity coupled with high undercooling by volatile lost of highly fractionated residual Cl-richer melts. The presence of biogenic carbon in granite peraluminous melts derived from metasedimentary sources and its later crystallization as graphite filaments opens a discussion on the carbon behavior during magma evolution, especially in highly polymerized melt framework.

Compiled volumetric data for fluor-, chlor-, and hydroxyl-apatite has been fitted to a pressure-volume-temperature ( P - V - T ) equation of state for volume calculation at elevated P and T . The regressions were used to assess the potential of apatite inclusions in garnet for thermobarometric applications, according to the pressurization of inclusions resulting from elastic differences between the inclusion and host minerals. Isomeke contours (lines in pressure temperature space, representing permissible entrapment conditions that yield a given inclusion pressure) were calculated and show that apatite inclusions in garnet are a particularly useful barometer, owing to the large differences in the bulk moduli and similar thermal expansivities between apatite and garnet. Heating experiments were conducted on fluorapatite inclusions in andraditic garnets from the Casting Copper skarn, Nevada, to assess the variation in measured inclusion pressure with heating relative to that predicted with isotropic elastic theory. Negligible departures between theoretical and measured pressurization suggests no significant correction is needed for applying room- T inclusion pressure measurements for barometry constraints.

A new olivine-melt thermometer based on the partitioning of Ni ( DNiOl/liq $D_{\text{Ni}}^{\text{Ol/liq}}$ ), with a form similar to the Beattie (1993)DMgOl/liq $D_{\text{Mg}}^{\text{Ol/liq}}$ thermometer, is presented in this study. It is calibrated on a data set of 123 olivine-melt equilibrium experiments from 16 studies in the literature that pass the following five filters: (1) 1 bar only, (2) analyzed totals between 99.0–101.0 wt% for olivine and 98.5–101.0 wt% for quenched glasses, (3) olivine is the only silicate phase in equilibrium with the melt, (4) the NiO concentration is ≥ 0.1 wt% in olivine and ≥ 0.01 wt% in quenched glass, and (5) no metallic phase is present other than the capsule. The final data set spans a wide range of temperatures (1170–1650 °C), liquid compositions (37–66 wt% SiO 2 ; 4–40 wt% MgO; 107–11 087 ppm Ni), and olivine compositions (Fo 36-100 ; 0.10–15.7 wt% NiO). The Ni-thermometer recovers the 123 experimental temperatures within ±29 °C (1σ), with an average residual of 0 °C. A re-fitted version of the Mg-thermometer of Beattie (1993), calibrated on the same 123 experiments as for the Ni-thermometer, results in an average residual of 1 ± 26 °C (1σ). When both thermometers are applied to the same 123 experiments, the average Δ T ( T Mg – T Ni ) is 1 ± 29 °C (1σ), which confirms that the Mg- and Ni-thermometers perform equally well over a wide range of anhydrous melt composition and temperature at 1 bar. The pressure dependence of the Ni-thermometer under crustal conditions ( ≤ 1 GPa) is shown to be negligible through comparison with experimental results from Matzen et al. (2013), whereas the pressure dependence of the Mg-thermometer is up to 52 °C at ≤ 1 GPa (Herzberg and O’Hara 2002). Therefore, neglecting the effect of pressure when applying both thermometers to basalts that crystallized olivine at crustal depths ( ≤ 1 GPa) is expected to lead to negative Δ T ( T Mg – T Ni ) values ( ≤ –52 °C). Application of the two thermometers to nine mid-ocean ridge basalts results in an average Δ T of –3°, consistent with shallow crystallization of olivine under nearly anhydrous conditions. In contrast, application of the two thermometers to 18 subduction-zone basalts leads to an average Δ T of +112°; this large positive Δ T value cannot be explained by the effect of pressure, temperature or anhydrous melt composition. It is well documented in the literature that DMgOl/liq $D_{\text{Mg}}^{\text{Ol/liq}}$ is affected by dissolved water in the melt and that Mg-thermometers overestimate the temperature of hydrous basalts if an H 2 O correction is not applied (e.g., Putirka et al. 2007). Therefore, the reason why hydrous arc basalts have higher Δ T ( T Mg – T Ni ) values than MORBs may be because DNiOl/liq $D_{\text{Ni}}^{\text{Ol/liq}}$ is less sensitivite to water in the melt, which is supported by new Ni-partitioning results on three olivine-melt equilibrium experiments on a basaltic andesite with up to 5 wt% H 2 O. More hydrous experiments are needed to confirm that the Ni-thermometer can be applied to hydrous melts without a correction for H 2 O in the melt.

Many plutons preserve evidence of magma mixing between hydrous mafic magmas and resident felsic crystal-rich mushes. To investigate water transfer processes in such systems following thermal equilibration, we conducted 24 h experiments to establish the petrological evolution of a water-undersaturated (4 wt% H 2 O in the interstitial melt) quartz-bearing dacite crystal mush (0.5−0.8 in crystal fraction) intruded by a water-saturated (≥6 wt% H 2 O), initially crystal-free, andesite magma at 950 °C and 4 kbar (12 km depth). Our results show isothermal undercooling resulting from a change in liquidus temperatures of the interacting magmas due to their changing water content. Specifically, mafic samples dramatically crystallize during water escape into the felsic end-members and consequent increase in liquidus temperature. Conversely, the addition of water to the felsic mush reduces the liquidus temperature, leading to an increase in melt fraction. The experiments provide insights into how volatiles contribute to crystal mush rejuvenation (i.e., increase of melt fraction). However, H 2 O diffusion alone is not sufficient to promote melt extraction from short- and long-lived mushes in the Earth’s crust.

Pressure is one of the key variables that controls magmatic phase equilibria. However, estimating magma storage pressures from erupted products can be challenging. Various barometers have been developed over the past two decades that exploit the pressure-sensitive incorporation of jadeite (Jd) into clinopyroxene. These Jd-in-clinopyroxene barometers have been applied to rift zone magmas from Iceland, where published estimates of magma storage depths span the full thickness of the crust, and extend into the mantle. However, tests performed on commonly used clinopyroxene-liquid barometers with data from experiments on H 2 O-poor tholeiites in the 1 atm to 10 kbar range reveal substantial pressure-dependent inaccuracies, with some models overestimating pressures of experimental products equilibrated at 1 atm by up to 3 kbar. The pressures of closed-capsule experiments in the 1–5 kbar range are also overestimated, and such errors cannot be attributed to Na loss, as is the case in open furnace experiments. The following barometer was calibrated from experimental data in the 1 atm to 20 kbar range to improve the accuracy of Jd-in-clinopyroxene barometry at pressures relevant to magma storage in the crust: P(kbar)=− 26.27+39.16T(K)104lnXJdCpxXNaO0.5liqXAlO1.5liq(XSiO2liq)2− 4.22ln⁡ (XDiHdCpx)+78.43XAlO1.5liq+393.81(XNaO0.5liqXKO0.5liq)2 $$\begin{array}{} P\big(\text{kbar}\big)=-26.27+39.16 \displaystyle\frac{T(\text{K})}{10^4}\ln\left[\frac{\text{X}^{\text{Cpx}}_{\text{Jd}}}{\text{X}^{\text{liq}}_{\text{NaO}_{0.5}}\text{X}^{\text{liq}}_{\text{AlO}_{1.5}}\big(\text{X}^{\text{liq}}_{\text{SiO}_{2}}\big)^2}\right] -4.22\ln\big(\text{X}^{\text{Cpx}}_{\text{DiHd}}\big)+78.43 \text{X}^{\text{liq}}_{\text{AlO}_{1.5}}+393.81\big(\text{X}^{\text{liq}}_{\text{NaO}_{0.5}}\text{X}^{\text{liq}}_{\text{KO}_{0.5}}\big)^2 \end{array} $$ This new barometer accurately reproduces its calibration data with a standard error of estimate (SEE) of ±1.4 kbar, and is suitable for use on hydrous and anhydrous samples that are ultramafic to intermediate in composition, but should be used with caution below 1100 °C and at oxygen fugacities greater than one log unit above the QFM buffer. Tests performed using with data from experiments on H 2 O-poor tholeiites reveal that 1 atm runs were overestimated by less than the model precision (1.2 kbar); the new calibration is significantly more accurate than previous formulations. Many current estimates of magma storage pressures may therefore need to be reassessed. To this end, the new barometer was applied to numerous published clinopyroxene analyses from Icelandic rift zone tholeiites that were filtered to exclude compositions affected by poor analytical precision or collected from disequilibrium sector zones. Pressures and temperatures were then calculated using the new barometer in concert with Equation 33 from Putirka (2008). Putative equilibrium liquids were selected from a large database of Icelandic glass and whole-rock compositions using an iterative scheme because most clinopyroxene analyses were too primitive to be in equilibrium with their host glasses. High-Mg# clinopyroxenes from the highly primitive Borgarhraun eruption in north Iceland record a mean storage pressure in the lower crust (5.7 kbar). All other eruptions considered record mean pressures in the mid-crust, with primitive clinopyroxene populations recording slightly higher pressures (3.1–3.6 kbar) than evolved populations (2.6–2.8 kbar). Thus, while some magma processing takes place in the shallow crust immediately beneath Iceland’s central volcanoes, magma evolution under the island’s neovolcanic rift zones is dominated by mid-crustal processes.

The extent to which sulfur dissolves in silicate melts saturated in an immiscible sulfide phase is a fundamental question in igneous petrology and plays a primary role in the generation of magmatic ore deposits, volcanic degassing, and planetary differentiation. In igneous systems, sulfide melts can be described as FeS-NiS-CuS 0.5 solutions with Fe/(Fe+Ni+Cu) significantly less than 1. Despite the presence of Ni and Cu in the sulfide, however, most experimental studies to date have concentrated on the effects of silicate melt composition on sulfur solubility and have used essentially pure FeS as the sulfide liquid. We have carried out 49 new experiments at pressures of 1.5–24 GPa and temperatures of 1400 to 2160 °C to investigate the effects of sulfide composition on sulfur solubility as well as extending the pressure and temperature ranges of the available data on sulfide saturation. We find that in the compositional range of most igneous sulfide melts [Fe/(Fe+Ni+Cu) > 0.6] sulfur solubility decreases linearly with Fe content such that at Fe/(Fe+Ni+Cu) of 0.6 the sulfur content at saturation is 0.6 times the value at pure FeS saturation. At lower values of Fe/(Fe+Ni+Cu), however, deviations from this ideal solution relationship need to be taken into consideration. We have treated these non-idealities by assuming that FeS-NiS-CuS 0.5 liquids approximate ternary regular solutions. We have fitted our data, together with data from the literature (392 in total), to equations incorporating the effects of silicate melt composition, sulfide liquid composition, and pressure on the solubility of sulfur at sulfide saturation ([S] SCSS ). The temperature dependence of [S] SCSS was assumed either to be an unknown or was taken from 1 bar thermodynamic data. The most important best-fit silicate melt compositional term reflects the strongly positive dependence of [S] SCSS on the FeO content of the silicate melt. The best-fit value of this parameter is essentially independent of our assumptions about temperature dependence of [S] SCSS or the solution properties of the sulfide. All natural compositions considered here exhibit positive dependences of [S] SCSS on temperature and negative dependences on pressure, in accord with previous studies using smaller data sets.

The relationship between bond valence and structural energy has never been fully explored, although several predictive models have assumed some simple relationship between the two. Some of these models relate energy only to bond valence, while others also take into account other factors, such as bond character. We examined periodic trends in bond dissociation energies as a function of their ionicity, covalency, and metallicity, defined in terms of the electronegativity values of the atoms involved. A statistical model was optimized to describe these trends, allowing us to generate rough bond energy vs. bond valence curves. The shapes of these curves vary dramatically as a function of bond character, and are strongly influenced by the lone-pair bond-weakening effect. The curve shapes can be used to rationalize several chemical trends, including the preferred structures of compounds with different bond types, the prevalence of peroxide and persulfide minerals, preferred bond lengths in oxides, and the p K a values of (hydr)oxy-acids. The last is perhaps the most important, because some valence-based acidity models are in current use, despite the fact that some aspects of their rationale are unclear.

Meteorite impacts produce shocked minerals in target rocks that record diagnostic high-pressure deformation microstructures unique to hypervelocity processes. When impact craters erode, detrital shocked minerals can be transported by fluvial processes, as has been demonstrated through studies of modern alluvium at some of the largest known impact structures. However, the ultimate fate of distally transported detrital shocked minerals in fluvial systems is not well understood and is an important parameter for constraining the location of a source crater. In South Africa, detrital shocked minerals from the 2020 Ma Vredefort impact structure have been documented in the Vaal River basin, downriver from the structure. Here, we report results of an extensive microstructural survey of detrital zircon from the Orange River basin and the Atlantic coast of South Africa to search for the presence of far-traveled Vredefort-derived detrital shocked zircon grains in different modern sedimentary environments. Three shocked grains were found out of 11 168 grains surveyed (0.03%) by scanning electron microscopy, including two in beach sand on the Atlantic coast and one from a sandbar 15 km upstream from the mouth of the Orange River. Shock-produced {112} twins documented by electron backscatter diffraction in each of the three grains confirm their impact provenance, and U-Pb ages from 3130 to 3040 Ma are consistent with derivation from bedrock at the Vredefort impact structure. These results demonstrate the transport of Vredefort-derived shocked zircon to the coast via the Vaal-Orange river system, which requires 1940 km of fluvial transport from their point source on the Kaapvaal craton to the Atlantic coast passive margin. These results further demonstrate that shocked zircon grains can be detected in detrital populations at abundances <1%, and can ultimately be transported outside their basin of origin when they arrive at continental margins. Detrital shocked zircon thus constitutes long-lived evidence of former impacts, as they retain microstructural evidence of shock deformation, as well as geochemical (U-Th-Pb) fingerprints of their source terrain. The study of detrital shocked minerals uniquely merges impact cratering with sedimentology, as identification of detrital grains with diagnostic shock microstructures in siliciclastic sediments can be applied to search the sedimentary record for evidence of eroded impact structures of any age, from the Phanerozoic to the Hadean, which can aid in reconstructing the impact record of Earth.

The concentrations of Fe, Al, and Ni and their distributions were determined for all known natural assemblages of ferropericlase (fPer) and bridgmanite (Bridg), coexisting as inclusions in deep-mantle diamonds from Brazil, Canada, Guinea, and South Australia. Based upon these data, it is likely that some areas within the deep lower mantle are iron-rich and differ markedly from a pyrolitic composition. In the lowermost lower mantle, Bridg is Al-rich and fPer is Ni-poor, witnessing the presence of a free metallic phase in the mineral-forming environment. The iron partitioning in the Bridg + fPer association [ KDBridg-fPer $\begin{array}{} K^{\text{Bridg-fPer}}_{\text{D}} \end{array} $ = ([Fe/Mg] Bridg )/([Fe/Mg] fPer ) at ] in juvenile diamond inclusions is as low as 0.1–0.2. During ascent of the diamonds with their inclusions to the surface, the KDBridg-fPer $\begin{array}{} K^{\text{Bridg-fPer}}_{\text{D}} \end{array} $ eventually increases to values of 0.4–0.5 and even as high as 0.7. The details of the element partitioning between natural Bridg and fPer in the lower mantle are as follows: iron in Bridg is ferrous Fe 2+ in the A site, substituting for Mg 2+ ; almost all iron in fPer is ferrous Fe 2+ ; the share of ferric Fe 3+ iron in fPer is Fe 3+ /ΣFe = 8–12 at%; iron concentrations in both Bridg and fPer increase with depth (pressure), reflecting the increasing Fe content in the lower part of the lower mantle, different from that of a pyrolitic model. Al in Bridg is mainly in the cation site B and partly in the cation site A, in both cases substituting for Si, Mg, and Fe with vacancy formation; and in the case of Al positioning into both B and A sites, a charge-balanced reaction occurs. The natural samples show very diverse KDBridg-fPer $\begin{array}{} K^{\text{Bridg-fPer}}_{\text{D}} \end{array} $ values and elemental distribution that cannot be simply explained by our current understanding on alumina dissolution in Bridg and the spin transition of Fe 2+ in fPer. These major differences between experimental results and observations in natural samples demonstrate the complex, inhomogeneous iron speciation and chemistry in the lower mantle.

Visual inspection (optical microscope point counting) and silica abundance show that laminated shale from the Late Cretaceous of Colombia contains high levels of detrital quartz silt and sand particles. Closer examination using the charge contrast imaging (CCI) technique, however, illustrates that much of the quartz is authigenic micro-quartz, and thus not exclusively of detrital origin. In addition, many “sand” grains that otherwise appear to represent simple detrital quartz particles are actually of biogenic origin, representing the tests of agglutinated foraminifera, formed from cemented silt-sized quartz particles. Finally, CCI shows that original detrital grains have undergone authigenic modification, with both syntaxial overgrowths and micro-quartz. Without recognition of these features, the relative proportion of detrital quartz (sand) would otherwise be greatly overestimated, with important implications for environmental interpretation. Furthermore, the recognition of biogenic structures, including agglutinated foraminifera, provides additional environmental information that otherwise could be easily overlooked.

The compressibility and structural behavior of the novel Mg 2 Fe 2 O 5 oxide has been investigated by in situ single-crystal X-ray diffraction in a diamond-anvil cell up to a pressure of 17 GPa. The bulk compressibility of Mg 2 Fe 2 O 5 can be described using a second-order Birch-Murnaghan equation of state (BM2 EoS) with V 0 = 352.4(2) Å 3 and K 0 = 171(4) GPa. Three linear BM2 EoS were used to describe the axial compressibility of Mg 2 Fe 2 O 5 , which was found to be highly anisotropic. The a and b lattice parameters have very similar compressibilies, with a 0 = 2.8917(11) Å and linear modulus M a = 572(16) GPa and b 0 = 9.736(3) Å and linear modulus M b = 583(15) GPa, respectively. The c -axis is the most compressible direction as indicated by the smaller linear modulus [ c 0 = 12.520(15) Å and M c = 404(28) GPa]. The Mg 2 Fe 2 O 5 structure consists of edge-sharing octahedra alternating with layers of trigonal prisms. The compression behavior of the M-O bonds of the M1 and M2 octahedra and of the M3 prisms depend on their location in either an edge-sharing environment, which makes them stiffer, or a corner-sharing environment where they have more freedom to distort and compress. The main compression mechanism consists of a polyhedral tilting around the M2-O1-M2 angle, which decreases with increasing pressure. Mg 2 Fe 2 O 5 has recently been added to the list of stable end-members of phases with M 4 O 5 stoichiometry, making it a potentially relevant phase in the Earth’s upper mantle and transition zone. To develop thermodynamic activity-composition models for high-pressure phases, it is crucial to know the accurate elastic parameters of each individual end-member. Currently these have only been measured for Mg 2 Fe 2 O 5 (this study) and Fe 4 O 5 .

The thermo-elastic behavior of synthetic single crystals of grossular garnet (Ca 3 Al 2 Si 3 O 12 ) has been studied in situ as a function of pressure and temperature separately. The same data collection protocol has been adopted to collect both the pressure-volume ( P - V ) and temperature-volume ( T - V ) data sets to make the measurements consistent with one another. The consistency between the two data sets allows simultaneous fitting to a single pressure-volume-temperature Equation of State (EoS), which was performed with a new fitting utility implemented in the latest version of the program EoSFit7c. The new utility performs fully weighted simultaneous fits of the P - V - T and P - K - T data using a thermal pressure EoS combined with any P - V EoS. Simultaneous refinement of our P - V - T data combined with that of K T as a function of T allowed us to produce a single P - V - T - K T equation of state with the following coefficients: V0=1664.46(5)A˚3,KTO=166.57(17)GPa andK′=4.96(7)α(300K,1bar)=2.09(2)×10−5K−1 $$ V_0 = 1664.46(5)\, {\rm\mathring A}\,^3 , K_{\text{TO}} = 166.57(17) \text{ GPa and } K'= 4.96(7)\, \rm\alpha_{(300 \;K,\; 1 {bar})} = 2.09(2) \times 10^{-5}\; K^{-1} $$ with a refined Einstein temperature (θ E ) of 512 K for a Holland-Powell-type thermal pressure model and a Tait third-order EoS. Additionally, thermodynamic properties of grossular have been calculated for the first time from crystal Helmholtz and Gibbs energies, including the contribution from phonons, using density functional theory within the framework of the quasi-harmonic approximation.

Carbonatites are rare igneous carbonate-rich rocks. Most carbonatites contain a large number of accessory oxide, sulfide, and silicate minerals. Baddeleyite (ZrO 2 ) and zircon (ZrSiO 4 ) are common accessory minerals in carbonatites and because these minerals host high concentrations of U and Th, they are often used to determine the ages of formation of the carbonatite. In an experimental study, we constrain the stability fields of baddeleyite and zircon in Ca-rich carbonate melts with different silica concentrations. Our results show that SiO 2 -free and low silica carbonate melts crystallize baddeleyite, whereas zircon only crystallizes in melts with higher concentration of SiO 2 . We also find that the zirconsilicate baghdadite (Ca 3 ZrSi 2 O 9 ) crystallizes in intermediate compositions. Our experiments indicate that zircon may not be a primary mineral in a low-silica carbonatite melt and care must be taken when interpreting zircon ages from low-silica carbonatite rocks.

Polarized FTIR spectroscopic measurements of 11 natural wolframite single crystals from different occurrences revealed the common presence of structurally bound OH groups in their crystal lattice, with potential influence on the properties of thisse geologically and technologically important group of compounds. Despite differences in the appearance of the OH absorption pattern, dependent among other on the end-member ratio, two types of “intrinsic” OH defects could be discerned from detailed studies of the pleochroic behavior of the absorption bands both at 80 K and room temperature. The accompanying chemical analyses by the electron microprobe helped to clearly identify the substitution trend W 6+ + O 2– ↔ (Nb,Ta) 5+ + OH – as the prevailing hydrogen incorporation mechanism into wolframite. The assignment of the observed IR absorption phenomena to hydrous defects was confirmed by the results of deuteration experiments and the negligible contribution of included impurities to the FTIR spectra in the OH absorption region. The results obtained in this study of natural wolframite crystals can be used to detect and analyze hydrous defects in synthetic technologically important tungstates.

Distinctive magmatic-hydrothermal, tourmaline-rich features have developed in the Heemskirk and Pieman Heads granites from western Tasmania, Australia. They are categorized as tourmaline-rich patches, orbicules, cavities, and veins, based on their distinctive morphologies, sizes, mineral assemblages, and contact relationships with host granites. These textural features occur in discrete layers in the roof zone of granitic sills within the Heemskirk and Pieman Heads granites. Tourmaline patches commonly occur below a tourmaline orbicule-rich granitic sill. Tourmaline-filled cavities have typically developed above the tourmaline-quartz orbicules in the upper layer of the white phase of the Heemskirk Granite. Tourmaline-quartz veins penetrate all exposed levels of the granites, locally cutting tourmaline orbicules and cavities. The tourmalines are mostly schorl (Fe-rich) and foitite, with an average end-member component of schorl 45 dravite 6 tsilaisite 1 uvite 0 Fe-uvite 3 foitite 31 Mg-foitite 4 olenite 10 . Element substitutions of the tourmalines are controlled by FeMg −1 , Y Al X □(R 2+ Na) −1 , and minor Y AlO(R 2+ OH) −1 (where R 2+ = Fe 2+ + Mg 2+ + Mn 2+ ) exchange vectors. Several trace elements in tourmaline have consistent chemical evolutions grouped from tourmaline patches, through orbicules and cavities, to veins. There is a progressive decrease of most transition and large ion lithophile elements, and a gradual increase of most high-field strength elements. These compositional variations in the different tourmaline-rich features probably relate to element partitioning occurring in these phases due to volatile exsolution and fluxing of aqueous boron-rich fluids that separated from the granitic melts during the emplacement of S-type magmas into the shallow crust (4 to 5.5 km). Tourmalines from the Heemskirk Granite are enriched in Fe, Na, Li, Be, Sn, Ta, Nb, Zr, Hf, Th, and rare earth elements relative to the tourmalines from the Pieman Heads Granite, but depleted in Mg, Mn, Sc, V, Co, Ni, Pb, Sr, and most transition elements. These results imply that bulk compositions of the host granites exert a major control on the chemical variations of tourmalines. The trace element compositions of tourmalines from the Sn-mineralized Heemskirk Granite are different from those of the barren Pieman Heads Granite. Trace element ratios (e.g., Zn/Nb, Co/Nb, Sr/Ta, and Co/La) and Sn concentrations in tourmaline can distinguish the productive Heemskirk Granite from the barren Pieman Heads Granite.

Tricalcium aluminate (cement clinker phase), gypsum, katoite, ettringite, and calcium monosulfoaluminate hydrate (abbreviated as kuzelite) are the major minerals in the hydration reaction of tricalcium aluminate in the presence of gypsum and have critical impacts on the kinetics and thermodynamics of early-age cement hydration mechanisms. Here, spectroscopic analysis of these minerals is conducted using scanning transmission X-ray microscopy (STXM). Their Ca L 2,3 -edge near edge X-ray absorption fine structure (NEXAFS) spectra are measured and correlated to the known Ca coordination environments. The results indicate that these minerals have unique Ca environments that can be differentiated from one another based on the intensities and positions of the absorption peaks at 346.5–348.5 and 350.5–351.5 eV. It is concluded that Ca in tricalcium aluminate (cubic and orthorhombic polymorphs) and katoite is in cubic-like coordination with negative 10 Dq , whereas Ca is in an octahedral-like coordination with positive 10 Dq in ettringite, gypsum, and kuzelite. For tricalcium aluminate, the Ca atoms in both polymorphs are in similar chemical environments with slightly more distortion in the orthorhombic polymorph. As a common issue in STXM experiments, absorption saturation of NEXAFS spectra is also investigated. It is demonstrated that the optical density difference between pre- and post-edge absorption levels provides a reliable indication of the sample thickness in the systems studied. The present work provides a reference for the STXM study of the calcium (sulfo)aluminate reactions in cement hydration and natural aqueous environments, and in the former case, provides a more complete understanding of a system that may serve as a low-C alternative to Portland cement.

Fluorwavellite (IMA2015-077), Al 3 (PO 4 ) 2 (OH) 2 F·5H 2 O, the F analog of wavellite, is a new mineral from the Silver Coin mine, Valmy, Iron Point district, Humboldt County, Nevada, and the Wood mine, 5 miles NE of Del Rio, Cocke County, Tennessee; at both occurrences it is a low-temperature secondary mineral. Fluorwavellite is essentially identical to wavellite in appearance and physical properties. Optically, fluorwavellite is biaxial positive, with α = 1.522(1), β = 1.531(1), and γ = 1.549(1) (white light). Electron microprobe analyses (average of nine for each co-type locality) provided the empirical formulas Al 2.96 (PO 4 ) 2 (OH) 1.98 F 1.02 ·5H 2 O (+0.12 H) for the Silver Coin mine and Al 2.98 (PO 4 ) 2 (OH) 2.11 F 0.89 ·5H 2 O (+0.06 H) for the Wood mine. Fluorwavellite is orthorhombic, Pcmn , with the cell parameters determined on a Wood mine crystal: a = 9.6311(4), b = 17.3731(12), c = 6.9946(3) Å, V = 1170.35(11) Å 3 , and Z = 4. The five strongest lines in the X-ray powder diffraction pattern are [ d obs in Å ( I ) ( hkl )]: 8.53 (100) (020,110); 5.65 (26) (101); 3.430 (28) (141,012); 3.223 (41) (240); and 2.580 (28) (331,161,232). The structure of fluorwavellite ( R 1 = 3.42% for 1248 F o > 4σ F reflections) is the same as that of wavellite, differing only in having one of the two independent hydroxyl sites replaced by F. A survey of F contents in wavellite-fluorwavellite from the five most common genetic types of occurrence (fluid expulsion, hydrothermal ore alteration, pegmatite phosphate alteration, residual carbonate weathering, and sedimentary leached zone) shows that F content, and the occurrence of wavellite vs. fluorwavellite, does not correlate with the type of the occurrence. It is more likely related to the fluid activity of Al, P, and F, with pH probably being an important factor. The role that wavellite and fluorwavellite play in sequestering F in the environment may be significant.