Volume 107, Issue 3

The structures of cold-compressed basaltic glass were investigated at pressures up to 18 GPa using in situ X‑ray and neutron diffraction techniques to understand the physicochemical properties of deep magmas. On compression, basaltic glass changes its compression behavior: the mean O-O coordination number ( CN OO ) starts to rise while maintaining the mean O-O distance ( r OO ) above about 2–4 GPa, and then CN OO stops increasing, and r OO begins to shrink along with the increase in the mean coordination number of Al ( CN AlO ) above ~9 GPa. The change around 9 GPa is interpreted by the change in contraction mechanism from bending tetrahedral networks of glass to increasing oxygen packing ratio via the increase in CN AlO . The analysis of the oxygen packing fraction (η O ) under high pressure reveals that η O exceeds the value for dense random packing, suggesting that the oxygen-packing hypothesis recently proposed cannot account for pressure-induced structural transformations of silica and silicate glasses. The rise of the CN OO at 2–4 GPa reflects the elastic softening of fourfold-coordinated silicate glass, which may be the origin of anomalies of elastic moduli in basaltic glass at ~2 GPa previously reported by Liu and Lin (2014). The widths of both the first sharp diffraction peak and the principal peak show contrastive compression behaviors between modified silicate and silica glasses. This result suggests that modified silicate glasses represent different pressure evolutions in the intermediate- and extended-range order structures from those of silica glass, likely due to the presence of modifier cations and the resultant formations of smaller rings and cavity volume.

We show, by single-crystal diffraction studies in laser-heated diamond-anvil cells, that Ca 2 CO 4 orthocarbonate, which contains CO 4 4 − tetrahedra, can be formed already at ~20 GPa at ~1830 K, i.e., at much lower pressures than other carbonates with sp 3 -hybridized carbon. Ca 2 CO 4 can also be formed at ~89 GPa and ~2500 K. This very broad P-T range suggests the possible existence of Ca 2 CO 4 in the Earth’s transition zone and in most of the lower mantle. Raman spectroscopy shows the typical bands associated with tetrahedral CO 4 4− -groups. DFT-theory based calculations reproduce the experimental Raman spectra and indicate that at least in the athermal limit the phase assemblage of Ca 2 CO 4 + 2SiO 2 is more stable than 2CaSiO 3 + CO 2 at high pressures.

Dense hydrous magnesium silicates (DHMSs) are considered important water carriers in the deep Earth. Due to the significant effect of Fe on the stability of DHMSs, Fe-bearing Phase D (PhD) deserves much attention. However, few experiments have been conducted to determine the stability of PhD in different bulk compositions. In this study, we provide experimental constraints for the stability of PhD in the AlOOH-FeOOH-Mg 1.11 Si 1.89 O 6 H 2.22 system between 18 and 25 GPa at 1000–1600 °C, corresponding to the P-T conditions of the mantle transition zone and uppermost lower mantle. Fe 3+ -bearing PhD was synthesized from the FeOOH-Mg 1.11 Si 1.89 O 6 H 2.22 binary system with two different Fe 3+ contents. The resultant Al,Fe 3+ -bearing compositions are close to analog specimens of the fully oxidized mid-ocean ridge basalt (MORB) and pyrolite in the AlOOH-FeOOH-Mg 1.11 Si 1.89 O 6 H 2.22 ternary system. The substitution mechanism of Fe is shown to be dependent on pressure, and Fe 3+ occupies both Mg and Si sites in PhD at pressures below 21 GPa. In contrast, Fe 3+ only occupies Si site at pressures exceeding 21 GPa. The presence of Fe 3+ results in a slight reduction in the thermal stability field of PhD in the FeOOH-Mg 1.11 Si 1.89 O 6 H 2.22 system in comparison to Mg-bearing, Fe-free PhD. In contrast, Al,Fe 3+ -bearing PhD is more stable than Mg-bearing PhD in both MORB and pyrolite compositions. In this regard, Al,Fe 3+ -bearing PhD could act as a long-term water reservoir during subduction processes to the deep mantle.

Potassium isotopes may provide a novel approach for fingerprinting recycled sediments in the mantle due to the significant differences in K abundance and isotopic ratio between subducting sediment and the mantle. However, the behavior of K isotopes in sediments during subduction zone metamorphism is still unknown. Here we investigate K isotopic composition of a set of well-characterized high- to ultrahigh-pressure metasediments from the Schistes Lustrés nappe (western Alps), which represents marine sediments subducted down to ~90 km depth in a cold subduction zone, and their protoliths from the Lavagna nappe (Apennines, Italy). The metasediments display δ 41 K SRM 3141a values from –0.76‰ to –0.48‰, which are on average lower than the mantle value (–0.43‰) but similar to those of non-metamorphic equivalents (–0.79‰ to –0.49‰). No systemic variation of δ 41 K with metamorphic grade is observed, suggesting negligible K isotope fractionation in these sediments during prograde metamorphism. This is in accord with the limited loss of K during the entire metamorphic history as evidenced by the constancy of K/Rb and K/Cs ratios between metamorphic and non-metamorphic sediments and the absence of correlations of δ 41 K with K/Rb and K/Cs. The heterogeneous δ 41 K values of metasediments are most likely inherited from their protoliths, which experienced different degrees of chemical weathering depending on their provenances. Our results demonstrate that the variable and light K isotopic signatures in subducting sediments could be preserved to depths of at least 90 km along a cold geotherm gradient, indicating that the introduction of sediments into the mantle could produce K isotope heterogeneity in the source regions of mantle-derived lavas.

Ni and Co variations in primary martian magmas exhibit anomalous incompatible behavior, which has remained an unexplained conundrum. Because martian magmas are S-rich, and some trace metals are reported to have enhanced solubility in S-bearing magmas, we have carried out a series of experiments to evaluate the effect of high-S melts on the olivine/melt partitioning of Ni, Co, Mn, V, and Cr. Near-liquidus experiments on a synthetic primary martian mantle melt (Yamato-980459 [Y98]) were completed in a piston-cylinder apparatus at 0.75 GPa. Previous studies in S-free systems illustrate that the partition coefficients for these elements are dependent chiefly on D Mg(Ol/melt) (the partition coefficient defined as wt% Mg in olivine/wt% Mg in melt, a proxy for temperature), and were used to calibrate a predictive expression that includes the efects of temperature [i.e., D Mg(Ol/melt) ], melt composition, and oxygen fugacity. These predictive expressions are then used to isolate any efect in D M olivine/melt due to dissolved sulfur. The results show that S might have a small efect for Co, but not enough to change Co partitioning from compatible to incompatible in our experiments. The addition of a sulfur term to the D Co predictive expressions shows that nearly 8000 ppm of sulfur would be required in the melt (at liquidus temperature of Y98) for D Co to become <1. These S contents are two times higher than those of a sulfide-saturated melt at the P - T conditions of a martian mantle source region. Therefore, the anomalous incompatible behavior observed in these primary magma suites must be due to another mechanism. High temperature, oxygen fugacity, and diffusion are not viable mechanisms, but magma mixing, assimilation, or kinetic crystallization effects remain possibilities.

Gold mobilization, transfer, and concentration in the Earth’s crust are controlled by hydrothermal sulfur- and chloride-bearing fluids. Yet the exact chemical identity, structure, and stability of Au-bearing species and, in particular, the respective contributions of the sulfide (HS − ) and trisulfur ion ( S 3 ∙ − $\text{S}_{3}^{\bullet-}$ ) ligands to Au transport lack direct in situ evidence. Here we employed high energy resolution fluorescence detection X‑ray absorption spectroscopy (HERFD-XAS) on aqueous sulfate/sulfide/ S 3 ∙ − $\text{S}_{3}^{\bullet-}$ -bearing solutions at typical hydrothermal temperatures and pressures ( T = 350 °C, P = 600 bar) to reveal differences in dissolved Au spectral signatures indicative of contrasting fluid-phase Au speciation as a function of acidity and redox conditions. Combined with in situ Au solubility measurements and quantum-chemical and thermodynamic modeling, our spectroscopic data provide direct evidence for the Au(HS)S ͞3 and Au(HS)S ͞2 complexes predominant at acidic-to-neutral and alkaline conditions, respectively. Our findings thus directly confirm a recent speciation scheme for Au in aqueous S-bearing fluids established using less direct methods, and highlight an important role of the trisulfur ion in gold mobilization and concentration in hydrothermal-magmatic deposits associated with subduction zones. More generally, our results show that HERFD-XAS enables the identification of structural and coordination features in metal complexes virtually unresolvable using classical XAS techniques. By avoiding limitations of less direct techniques, our integrated high-resolution spectroscopic approach opens perspectives for studies of the speciation and solubility of gold and other metals in high T-P fluids, and potentially silicate melts, inaccessible to direct observation in nature.

The formation and shock history of ureilite meteorites, a relatively abundant type of primitive achondrites, has been debated for decades. For this purpose, the characterization of carbon phases can provide further information on diamond and graphite formation in ureilites, shedding light on the origin and history of this meteorite group. In this work, we present X‑ray diffraction and micro-Raman spectroscopy analyses performed on diamond and graphite occurring in the ureilite Yamato 74123 (Y-74123). The results show that nano- and microdiamonds coexist with nanographite aggregates. This, together with the shock-deformation features observed in olivine, such as mosaicism and planar fractures, suggest that diamond grains formed by a shock event (≥15 GPa) on the ureilitic parent body (UPB). Our results on Y-74123 are consistent with those obtained on the NWA 7983 ureilite and further support the hypothesis that the simultaneous formation of nano- and microdiamonds with the assistance of a Fe-Ni melt catalysis may be related to the heterogeneous propagation and local scattering of the shock wave. Graphite geothermometry revealed an average recorded temperature ( T max ) of 1314 °C (±120 °C) in agreement with previously estimated crystallization temperatures reported for graphite in Almahata Sitta ureilite.

We investigated the structural, vibrational, and electrical transport properties of natural kaolinite and its high-pressure polymorphs by Raman scattering and electrical conductivity measurements at 293–673 K and up to 10.0 GPa using diamond-anvil cell. Upon compression, kaolinite underwent two structural transitions from kaolinite I to kaolinite II to kaolinite III phases at pressures of 2.9 and 6.5 GPa, respectively, which was disclosed by the inflection point in the pressure-dependent Raman shifts and electrical conductivity. Upon decompression, kaolinite III directly transformed to kaolinite I at 0.8 GPa without the appearance of kaolinite II. Additionally, the influence of temperature on the structural transformation of natural kaolinite was explored by high-temperature and high-pressure electrical conductivity measurements and negative temperature-dependent transition pressure correlations were obtained. A phase diagram of natural kaolinite was established for the first time and the kaolinite I-kaolinite II and kaolinite II-kaolinite III phase transition boundaries were determined: P (GPa) = 4.298–0.00462 T (K) and P (GPa) = 8.895–0.00799 T (K), respectively. Furthermore, our acquired phase diagram can be applied to understand the stability field of high-pressure polymorphs of kaolinite in the Earth’s interior and may provide a phase transition model for other kaolin-group minerals.

The textures and geochemical characteristics of the rocks in layered intrusions potentially provide insights into the physicochemical processes that have taken place in mafic magma chambers. Diverse exsolution textures of Fe-Ti oxides in layered intrusions may record the variation of subsolidus temperature and oxygen fugacity ( f O2 ) of cooling magma chambers. Here we investigated ilmenite-hematite solid solution (Ilm ss ) relationships evident in preserved intergrowths of magnetite-rutile and ilmenite-hematite in the gabbro of the Xinjie layered intrusion. The crystallographic orientation and 3D morphology of the two intergrowth types constrain the transformation mechanism of the exsolution textures from Ilm ss . The results reveal that the interface of the ilmenite-hematite intergrowth is more energetically favorable than that of the magnetite-rutile symplectite when they are transformed from Ilm ss on cooling. The QUILF equilibria suggests that the magnetite-rutile symplectite can be transformed from Ti-rich ilmenite with Ilm ≥0.85 above 550 °C when the subsolidus T-f O2 trend is bufered by the biotite-ilmenite-feldspar-ulvöspinel (KUIlB) mineral assemblages crystallized from hydrated mafic magmas. The magnetite-rutile symplectite may be used as a unique texture indicator of magma hydration in the evolution history of terrestrial, martian, and lunar magmas.

Single crystals of Al-free, ferromagnesian jefbenite up to 200 μm in size have been synthesized at 15 GPa and 1200 °C in a 1200 tonne multi-anvil press from a starting composition in the forsteritefayalite-magnetite-water system. This phase has the approximate formula Mg 2.62 Fe 20.87+ Fe 31.63+ Si 2.88 O 12 and is observed to coexist with a Ca-free clinopyroxene plus what appears to be quenched melt. The crystal structure has been refined from single-crystal X‑ray difraction data and is similar to that determined for natural Al-bearing jeffbenite, Mg 3 Al 2 Si 3 O 12 , reported from inclusions in superdeep diamonds. The structure is a tetragonal orthosilicate in space group I 4̅2 d with a = 6.6449(4) Å, c = 18.4823(14) Å, and is structurally more closely related to zircon than to garnet. The T2 site is larger than T1, shares an edge with the M2 octahedron, and incorporates significant Fe 3+ . Because of the tetrahedral incorporation of trivalent cations, jeffbenite appears to be compositionally distinct from garnet. Previous speculations that the phase may only occur as a retrograde decompression product from bridgmanite are not supported by its direct synthesis under transition zone conditions. The phase has a calculated density of 3.93 g/cm 3 , which is indistinguishable from a garnet of comparable composition, and is a possible component in the mantle transition zone under oxidizing conditions or with Al-rich compositions.

A plausible origin of the seismically observed mid-lithospheric discontinuity (MLD) in the subcontinental lithosphere is mantle metasomatism. The metasomatized mantle is likely to stabilize hydrous phases such as amphiboles. The existing electrical conductivity data on amphiboles vary significantly. The electrical conductivity of hornblendite is much higher than that of tremolite. Thus, if hornblendite truly represents the amphibole varieties in MLD regions, then it is likely that amphibole will cause high electrical conductivity anomalies at MLD depths. However, this is inconsistent with the magnetotelluric observations across MLD depths. Hence, to better understand this discrepancy in electrical conductivity data of amphiboles and to evaluate whether MLD could be caused by metasomatism, we determined the electrical conductivity of a natural metasomatized rock sample. The metasomatized rock sample consists of ~87% diopside pyroxene, ~9% sodium-bearing tremolite amphibole, and ~3% albite feldspar. We collected the electrical conductivity data at ~3.0 GPa, i.e., the depth relevant to MLD. We also spanned a temperature range between 400 to 1000 K. We found that the electrical conductivity of this metasomatized rock sample increases with temperature. The temperature dependence of the electrical conductivity exhibits two distinct regimes. At low temperatures <700 K, the electrical conductivity is dominated by the conduction in the solid state. At temperatures >775 K, the conductivity increases, and it is likely to be dominated by the conduction of aqueous fluids due to partial dehydration. The main distinction between the current study and the prior studies on the electrical conductivity of amphiboles or amphibole-bearing rocks is the sodium (Na) content in amphiboles of the assemblage. Moreover, it is likely that the higher Na content in amphiboles leads to higher electrical conductivity. Pargasite and edenite amphiboles are the most common amphibole varieties in the metasomatized mantle, and our study on Na-bearing tremolite is the closest analog of these amphiboles. Comparison of the electrical conductivity results with the magnetotelluric observations constrains the amphibole abundance at MLD depths to <1.5%. Such a low-modal proportion of amphiboles could only reduce the seismic shear wave velocity by 0.4–0.5%, which is significantly lower than the observed velocity reduction of 2–6%. Thus, it might be challenging to explain both seismic and magnetotelluric observations at MLD simultaneously.

Isotopic fractionation has been linked to the lattice vibrations of materials through their phonon spectra. The Lamb-Mössbauer factor ( fLM ) has the potential to provide information about the lattice vibrations in materials. We constrain the temperature evolution of the fLM of γ- and ε-Fe at in situ high- P-T conditions between 1650 K and the melting point. We find that the vibrations of γ- and ε-Fe can be described using a quasiharmonic model with a pressure- and temperature-dependent Debye temperature computed from the measured fLM . From the Debye temperature, we derive the equilibrium isotopic fractionation β-factor of iron. Our results show that the quasiharmonic behavior of metallic iron would lower the value of lnβ Fe 57/54 by 0.1‰ at 1600–2800 K and 50 GPa when compared to the extrapolation of room temperature nuclear resonant inelastic X‑ray scattering data. Our study suggests that anharmonicity may be more prevalent in Fe metal than in lower mantle minerals at 2800 K and 50 GPa, a relevant condition for the core formation, and the silicate mantle may be isotopically heavy in iron.

Studies of the submarine alteration of basaltic glass may improve the understanding of crust-seawater interactions and the oceanic elemental cycle. Natural alteration processes such as the palagonitization of basaltic glass are complex, and their elucidation is crucial to the understanding of fluid-rock interactions. This study involves major and trace element and isotope mapping of a submarine-altered basaltic glass grain and reveals sequential development of alteration textures toward the grain core through the transition between unaltered glass and palagonite. The conversion from basaltic glass to palagonite in a low-temperature submarine environment results in enrichment in B, Rb, K, Li, H 2 O, U, Nb, Th, Ti, Cu, Ta, Zr, Hf, Ni, Sc, Fe, Cr, Pb, and Zn; and depletion in Si, Mg, Al, Sr, Na, Co, rare-earth elements, Ca, P, and V (in order of decreasing distribution coefficient). The glass-palagonite interface region has the highest high field strength element (HFSE) and Fe-Ti contents but the lowest Mg content, indicating that the Fe-Ti phases that host HFSE were precipitated first during initial palagonitization. At the same time, an inferred exchange of oxygen occurred, based on variation in δ 18 O, with values increasing from basaltic glass to palagonite. However, initial palagonite compositions were afected by subsequent precipitation and/or incorporation/adsorption of additional compounds such as Mg(OH) 2 scavenged from pore water.

There is a great abundance of sedimentary dolomite in the Proterozoic and Lower Paleozoic, but examples of primary dolomite are scarce in the Cenozoic. This discrepancy suggests a poorly understood but dramatic shift in the geochemical system that inhibited dolomite formation. Previous research on microbial-mediated dolomite formation demonstrated that microbial activity could promote disordered dolomite precipitation through the catalytic role of polysaccharides. However, the microbial-mediated model cannot explain some of the Precambrian dolomite for which there is no evidence of microbial origin. Here, we present an abiotic mechanism with dissolved silica catalyzed dolomite precipitation that provides new insight into this long-lasting “dolomite problem.” In this study, we demonstrate that the presence of 1–2 mM of aqueous Si(OH) 4 in high Mg:Ca ratio solutions at room temperature will promote disordered dolomite precipitation (with up to 48.7 mol% MgCO 3 ) and inhibit aragonite formation. Dissolved silica in solution also promotes Mg incorporation into the Ca-Mg carbonates. Dissolved silica possesses low-dipole moment and dielectric constant similar to hydrogen sulfide, dioxane, polysaccharide, and exopolymeric substances (EPS), which are catalysts in previously established room-temperature dolomite synthesis. The molecules with low-dipole moment adsorbed on the dolomite surface can lower the dehydration energy barrier of a surface Mg 2+ -water complex and promote dolomite nucleation and growth. This study provides a new model for abiotic sedimentary dolomite formation, which is likely to be responsible for the significant amount of primary dolomite in Earth history.

In situ high-pressure and high-temperature X-ray diffraction studies on magnesiochromite, MgCr 2 O 4 , and a natural chromite, (Mg,Fe)(Al,Cr) 2 O 4 , using a laser-heated diamond-anvil cell technique were performed at pressures to ~45 GPa. Our results on MgCr 2 O 4 at ~15 GPa showed temperature-induced dissociation of MgCr 2 O 4 to Cr 2 O 3 +MgO below ~1500 K and formation of modified ludwigite (mLd)-type Mg 2 Cr 2 O 5 +Cr 2 O 3 above ~1500 K. Above 20 GPa, only a single phase with the CaTi 2 O 4 -type structure of MgCr 2 O 4 was observed at 1400–2000 K. A second-order Birch-Murnaghan fit to pressure-volume data for the CaTi 2 O 4 -type phase of MgCr 2 O 4 yields zero-pressure volume ( V 0 ) = 264.4(8) Å 3 and bulk modulus ( K 0 ) = 185.4(4) GPa, and for the CaTi 2 O 4 -type structure of natural (Mg,Fe)(Al,Cr) 2 O 4 yields V 0 = 261(1) Å 3 and K 0 = 175.4(2) GPa. A second-order Birch-Murnaghan fit to pressure-volume data of mLd-type Mg 2 Cr 2 O 5 yields V 0 = 338.9(8) Å 3 and K 0 = 186.5(6) GPa. The obtained high-pressure phase relations of chromite spinels can be used as an indicator for shock pressure in impact rocks and meteorites. The bulk moduli of the high-pressure phases of MgCr 2 O 4 and FeCr 2 O 4 can help develop a thermodynamic model for Mg and Fe end-member spinels in the upper mantle and transition zone.

Thick sequences of silicic ignimbrites contain complex emplacement and cooling histories, often masking contacts between ignimbrite flow packages. Mineralogical and textural variations in these sequences are primarily a function of emplacement temperature and cooling time. Here, we focus on the use of the silica polymorph tridymite to understand the association of vapor-phase crystallization and devitrification within ignimbrite flow packages. As opposed to the common occurrence of cristobalite, the restricted domains in which we observe tridymite may provide more relevant constraints for interpreting post-emplacement devitrification and vapor-phase alteration. This study examines sections through the Whakamaru (New Zealand), Bishop (U.S.A.), and Grey’s Landing (U.S.A.) ignimbrites by combining textural observations with measurements of density, groundmass crystallinity, and the distribution and proportion of tridymite to cristobalite. The rheomorphic Grey’s Landing ignimbrite represents a high-temperature end-member scenario, with widely distributed tridymite (up to 20%) resulting from a high-magmatic temperature and rapid devitrification in a low-porosity deposit. In the welded Whakamaru and Bishop ignimbrites, metastable tridymite (up to 13%) is concentrated along boundaries between flow packages. Here tridymite is interpreted to crystallize in transient permeable zones, forming during vapor-phase alteration prior to compaction, where upper denser-welded flow materials serve as vapor seals. Our results suggest that tridymite may link the initial cooling and welding history of ignimbrites to vapor-phase alteration and devitrification, and may serve as a potential mineralogical fingerprint of depositional contacts, important for consideration of lateral transport of fluids in geothermal reservoirs.

The formation process of myrmekites in granitic rocks can help us to understand the mass transfer between minerals and hydrothermal fluids during the deuteric stage. The Toki granite, central Japan, has three types of myrmekites. Type A myrmekite is defined as a single layer. Type B myrmekite shows a composite texture consisting of two layers, namely, a myrmekite layer and an albite (Ab)-rich layer that is free of vermicular quartz. Type C has a composite texture with the following three layers: two myrmekite layers separated by one Ab-rich layer. Micropores are found in these myrmekites in the undeformed granite, which enable quantitative determinations of the volume decrease during myrmekite formation by measurement of the area of micropores. The areal relationship between the micropores and vermicular quartz in the myrmekites exhibited a high correlation (R 2 = 0.8352), thus indicating that the genesis of the micropores is evidently related to myrmekite formation. We derived the reaction equations for myrmekite formation based on the singular value decomposition method. The matrices for singular value decomposition involve the following volume factors: volume change during the reaction and volume ratios of the product minerals. The singular value decomposition indicates that the myrmekites are produced through the consumption of plagioclase and K-feldspar with an inflow of H 4 SiO 4 , Na + , and H + from the hydrothermal fluid, accompanied by an outflow of Al 3+ , Ca 2+ , and K + into the fluid, which constitute essential mass transfers during myrmekite formation. The diference of pH in the hydrothermal fluid and inflow amounts of H 4 SiO 4 and Na + can explain the reason why micropores occur in the myrmekites but not in the Ab-rich rim (layer); the smaller inflow of H 4 SiO 4 and Na + from the hydrothermal fluid with lower pH conditions yielded micropore production during myrmekitization, and the larger inflow of H 4 SiO 4 and Na + from the hydrothermal fluid with higher pH conditions yielded the formation of the Ab-rich rim (layer) with few micropores. The sequential variations in the chemical characteristics of the hydrothermal fluid during the sub-solidus conditions were characterized by a gradual decrease in H 4 SiO 4 (Si 4+ ), Fe 2+ , Mn 2+ , Mg 2+ , and Na + and a gradual increase in Ca 2+ , K + , H + , and F – .

Pink euclase of gem quality and centimeter size, presenting an unusual pink-orange coloration and a pink to orange pleochroism, was discovered near Livramento de Nossa Senhora, in Bahia State, Brazil. The origin of the pink coloration has been investigated using several spectroscopic techniques: UV-Vis-NIR spectroscopy, electron paramagnetic resonance (EPR), luminescence, and X‑ray absorption near edge structure (XANES). The coloration is mainly due to the presence of Mn 3+ substituted to octahedral Al 3+ that causes an intense split band at about 18 500 and 21 000 cm −1 . The crystal field splitting D q , crystal field stabilization energy (CFSE), and Racah parameter B for Mn 3+ are 2055.5 cm −1 , 147 kJ/mol, and 886 cm −1 , respectively. The Mn 3+ molar extinction coefficient varies as a function of polarization, between 23 and 55 L.mol − 1 ·cm −1 . An additional absorption band, near 24 000 cm −1 , together with the rising background toward the UV, tentatively assigned to the O → Fe 3+ OMCT, contributes to the pink-orange hue. The in-situ UV-Vis-NIR spectra on heating up to 500 °C show a color change toward an intense, stable pink color. CIE colorimetric parameters demonstrate that the color of the investigated euclase remains in the pink domain before and after heat treatment. In the absence of Mn 2+ , shown by EPR and luminescence, the presence of Mn 3+ evidences oxidative formation conditions due to contamination of the hydrothermal fluids by the surrounding host rock.

Tourmaline occurs widely within Dayishan ore field, Nanling Range, and is associated with magmatic-hydrothermal rare metal mineralization. Four types of tourmaline are recognized: (1) tourmaline in coarse-grained monzogranite (Tur-G1); (2) tourmaline in medium–fine-grained monzogranite (Tur-G2); (3) tourmaline aggregates associated with muscovite in greisen (Tur-Gr), showing a yellow core (Tur-Gry) and blue rim (Tur-Grb); and (4) quartz-vein-hosted tourmaline (Tur-V). In this study, we performed systematic investigations of in situ boron isotopic and elemental compositions of tourmalines in different granite, greisen, and quartz veins by EPMA and LA-MC-ICP-MS. Results show that almost all tourmalines exhibit schorl compositional affinity with extremely low Ca contents, high Fe/(Fe+Mg), and the calculated X-site occupancies in tourmalines show their affinities to the alkali group. Substitution processes of major element variations are dominantly caused by MgFe −1 , FeAl −1 , (Ca,Mg)(□ –1 ,Al –2 ), and R(Na,Mg) –1 exchange vectors. Based on geochemistry and petrology, Tur-G1, Tur-G2, and Tur-Gry precipitated from a boron-rich melt, while Tur-Grb and Tur-V crystallized from hydrothermal fluid. Many trace element concentrations overlap and most are <10 ppm. The significantly higher contents of Sn and Zn and positive Eu anomaly reflect the influence of an external fluid. Magmatic tourmalines fall into a narrow range of δ 11 B values between –15.58 and –14.09‰, indicating a single boron source of the granitic magma. Hydrothermal tourmalines display slightly lighter B isotopic compositions (–16.31 to –14.91‰), which are consistent with precipitation from externally derived fluids with lighter boron. Based on the isotopic and chemical compositional evidence, Sn and Zn may come from the host rock rather than granite.

A new organic mineral species, lazaraskeite, ideally Cu(C 2 H 3 O 3 ) 2 with two polytypes M 1 and M 2 , was discovered in the high elevation of the Santa Catalina Mountains, north of Tucson, Arizona, U. S.A. Both lazaraskeite- M 1 and -M 2 occur as euhedral individual crystals (up to 0.20 × 0.20 × 0.80 mm) or aggregates, with the former being more equant crystals and the latter bladed crystals elongated along the c axis. Associated minerals include chrysocolla, malachite, wulfenite, mimetite, hydroxylpyromorphite, hematite, microcline, muscovite, and quartz. Both polytypes are greenish-blue in transmitted light, transparent with white streak, and a vitreous luster. They are brittle and have a Mohs hardness of ~2; cleavage is perfect on {101}. No parting or twinning was observed. The measured and calculated densities are 2.12(2) and 2.138 g/cm 3 , respectively, for lazaraskeite- M 1 and 2.10(2) and 2.086 g/cm 3 for lazaraskeite- M 2 . Optically, lazaraskeite- M 1 is biaxial (−), with α = 1.595(3), β = 1.629(8), γ = 1.645(5), 2 V meas = 69(2)°, 2 V cal = 67°. Lazaraskeite- M 2 is also biaxial (−), with α = 1.520(5), β = 1.578(6), γ = 1.610(5), 2 V meas = 73(2)°, 2 V cal = 70°. Lazaraskeite is insoluble in water or acetone. An electron microprobe analysis for Cu and an Elemental Combustion System equipped with mass spectrometry for C yielded an empirical formula, based on 6 O apfu, Cu 1.01 (C 1.99 H 2.99 O 3 ) 2 for lazaraskeite- M 1 and Cu 1.01 (C 1.98 H 3.00 O 3 ) 2 for lazaraskeite- M 2 . The measured δ 13 C ‰ values are –37.7(1) and –37.8(1) for lazaraskeite- M 1 and -M 2 , respectively. Both lazaraskeite- M 1 and -M 2 are monoclinic with the same space group P 2 1/n . The unit-cell parameters are a = 5.1049(2), b = 8.6742(4), c = 7.7566(3) Å, β = 106.834(2)°, V = 328.75(2) Å 3 for M 1 and a = 5.1977(3), b = 7.4338(4), c = 8.8091(4) Å, β = 101.418(2)°, V = 333.64(3) Å 3 for M 2 . Lazaraskeite- M 1 is the natural analog of synthetic bis(glycolato)copper(II), Cu(C 2 H 3 O 3 ) 2 . Its crystal structure is characterized by layers made of octahedrally coordinated Cu 2+ cations and glycolate (C 2 H 3 O 3 ) – anionic groups. These layers, parallel to (101), are linked together by the strong hydrogen bonds (O-H···O = 2.58 Å). The CuO 6 octahedron is highly distorted, with four equatorial Cu-O bonds between 1.92 and 1.94 Å and two axial bonds at 2.54 Å. Lazaraskeite- M 2 has the same topology as lazaraskeite- M 1 and possesses all structural features of the low-temperature phase transformed from lazaraskeite- M 1 at 220 K (Yoneyama et al. 2013). The major differences between the two polytypes of lazaraskeite include: (1) M 1 has b > c , with β = 106.8°, whereas M 2 has b < c , with β = 101.4°; (2) the CuO 6 octahedron in M 1 is more elongated and distorted than in M 2 ; and (3) there is a relative change in the molecular orientation between the two structures. Lazaraskeite represents the first organic mineral that contains glycolate. Not only does its discovery imply that more glycolate minerals may be found, but also suggests that glycolate minerals may serve as a potential storage for biologically fixed carbon.

Bilihe is a porphyry gold deposit located in the northern margin of the North China Craton (NCC), Inner Mongolia, China. Different stages of quartz are well developed at this deposit. To document the history of quartz deposition, the fluid evolution and gold precipitation events of the deposit and the detailed oxygen isotope signatures of quartz from Bilihe were studied using high-resolution secondary ion mass spectroscopy (SIMS), then integrated with scanning electron microscope-cathodoluminescence (SEM-CL) and fluid inclusion microthermometry. The SEM-CL features show that the hydrothermal veins at Bilihe have a complex growth history, with multiple generations of quartz developed in each set of veins. Fluid inclusions in diferent quartz stages yield variable homogenization temperatures, ranging from 178 °C to above 600 °C. These quartz stages exhibit variable δ 18 O values of 3.5–15.4‰, corresponding to δ 18 O fluid ranging from –8.7 to 12.0‰. There are two abnormal peaks of δ 18 O quartz and δ 18 O fluid values occurring in a sub-generation of A type veins and auriferous-banded quartz veins, suggesting that the vein quartz may have experienced sporadic disequilibrium oxygen fractionation with water when crystallizing, thus resulting in local 18 O-enrichment. The overall δ 18 O fluid values, which show a gradual decrease from early to late stages, suggest a progressive decrease in the proportion of magmatic hydrothermal fluids. The relationship between quartz textures and gold occurrence shows that gold precipitated twice at Bilihe. The first precipitation in the UST quartz may have resulted from rapid cooling and indicates that the addition of meteoric water was not necessary for gold precipitation, whereas the progressive incursion of meteoric water probably had a significant efect on the second gold precipitation event.

Xenolithic corundum aggregates in Cretaceous mafic pyroclastics from Mount Carmel contain pockets of silicate melts with mineral assemblages [SiC (moissanite), TiC, Ti 2 O 3 (tistarite), Fe-Ti-Zr silicides/phosphides] indicative of magmatic temperatures and oxygen fugacity ( f O2 ) at least 6 log units below the iron-wüstite buffer (ΔIW ≤ –6). Microstructural evidence indicates that immiscible, carbon-rich metallic (Fe-Ti-Zr-Si-P) melts separated during the crystallization of the silicate melts. The further evolution of these metallic melts was driven by the crystallization of two main ternary phases (FeTiSi and FeTiSi 2 ) and several near-binary phases, as well as the separation of more evolved immiscible melts. Reconstructed melt compositions fall close to cotectic curves in the Fe-Ti-Si system, consistent with trapping as metallic liquids. Temperatures estimated from comparisons with experimental work range from ≥1500 °C to ca. 1150 °C; these probably are maximum values due to the solution of C, H, P, and Zr. With decreasing temperature ( T ), the Si, Fe, and P contents of the Fe-Ti-Si melts increased, while contents of Ti and C decreased. The increase in Si with declining T implies a corresponding decrease in f O2 , probably to ca. ΔIW-9. The solubility of P in the metallic melts declined with T and f O2 , leading to immiscibility between Fe-Ti-Si melts and (Ti,Zr)-(P,Si) melts. Decreasing T and f O2 also reduced the solubility of C in the liquid metal, driving the continuous crystallization of TiC and SiC during cooling. The lower- T metallic melts are richer in Cr, and to some extent V, as predicted by experimental studies showing that Cr and V become more siderophile with decreasing f O2 . These observations emphasize the importance of melt-melt immiscibility for the evolution of magmas under reducing conditions. The low f O2 and the abundance of carbon in the Mt. Carmel system are consistent with a model in which differentiating melts were fluxed by fluids that were dominated by CH 4 +H 2 , probably derived from a metal-saturated sublithospheric mantle. A compilation of other occurrences suggests that these phenomena may commonly accompany several types of explosive volcanism.