Volume 98, Issue 10

The alunite supergroup of minerals is a large hydroxy-sulfate mineral group, which has seen renewed interest following their discovery on Mars. Numerous reviews exist concerning nomenclature, formation, and natural occurrence of this mineral group. Sulfate minerals in general are widely studied and their vibrational spectra are well characterized. However, no specific review concerning alunite and jarosite spectroscopy and crystal structure has been forthcoming. This review focuses on the controversial aspects of the crystal structure and vibrational spectroscopy of jarosite and alunite minerals. Inconsistencies regarding band assignments especially in the 1000-400 cm -1 region plague these two mineral groups and result in different band assignments among the various spectroscopic studies. There are significant crystallographic and magnetic structure ambiguities with regards to ammonium and hydronium end-members, namely, the geometry these two ions assume in the structure and the fact that hydronium jarosite is a spin glass. It was also found that the synthetic causes for the super cell in plumbojarosite, minamiite, huangite, and walthierite are not known.

The high-grade metamorphic metasedimentary rocks that comprise the Wollaston Domain, northern Saskatchewan, are host to numerous REE-mineralized pegmatite bodies, including the Kulyk Lake monazite-apatite-Fe(Ti)-oxide occurrence. This occurrence, which is defined by a 3-5 cm wide sinouous zone of granoblastic monazite, apatite, and titanomagnetite, is enclosed within aplitic monzonite and granitic pegmatite dikes. Monazite in this dike was studied in detail using in situ laser ablationinductively coupled plasma-mass spectrometry (LA-ICP-MS) and LA-multi-collector (MC)-ICP-MS. A combination of in situ LA-ICP-MS trace element mapping, trace-element quantification, and U-Pb dating were used to identify a significant volume of partial resorbed xenocyrstic monazite and zircon cores within the monazite-apatite-Fe(Ti)-oxide zone. This xenocrystic monazite is locally characterized by anomalously high As, V, Mo, and Eu concentrations and high (La/Yb) CN (i.e., >1000) consistent with their derivation from metalliferous black shales. The U-Pb age distribution of the inherited monazite and zircon populations matches that of the middle- to upper-Wollaston Group sedimentary succession. The latter was confirmed by in situ Sm-Nd isotope systematics measured by LA-MCICP- MS that yielded εNd (1830Ma) between -5.0 and -5.7 consistent with derivation from Wollaston Group metasediment. The crystallization of ~1830 Ma anatectic overgrowths on xenocrystic cores is indistinguishable from monazite crystallization in the aplitic monzonite dike hosting the monaziteapatite- Fe(Ti)-oxide bodies. This study reveals the potential importance of metalliferous monazite-rich lithologies in the anatectic zone to these pegmatite-hosted REE occurrences and suggests that entrainment and magmatic segregation mechanisms may have helped to concentrate monazite, apatite, and Fe(Ti)-oxide prior to final emplacement of the aplite-pegmatite dikes. Similar processes may have occurred regionally and in other high-grade metamorphic terrains worldwide that are endowed with metalliferous metasedimentary protoliths.

We present a calibration for attenuated total reflectance (ATR) micro-FTIR for analysis of H 2 O in hydrous glass. A Ge ATR accessory was used to measure evanescent wave absorption by H 2 O within hydrous rhyolite and other standards. Absorbance at 3450 cm -1 (representing total H 2 O or H 2 Ot) and 1630 cm -1 (molecular H 2 O or H 2 Om) showed high correlation with measured H 2 O in the glasses as determined by transmission FTIR spectroscopy and manometry. For rhyolite, wt%H 2 O = 245(±9)·A 3450 - 0.22(±0.03) and wt%H 2 Om = 235(±11)·A 1630 - 0.20(±0.03) where A 3450 and A 1630 represent the ATR absorption at the relevant infrared wavelengths. The calibration permits determination of volatiles in singly polished glass samples with spot size down to ~5 μm (for H 2 Orich samples) and detection limits of ~0.1 wt% H 2 O. Basaltic, basaltic andesite and dacitic glasses of known H 2 O concentrations fall along a density-adjusted calibration, indicating that ATR is relatively insensitive to glass composition, at least for calc-alkaline glasses. The following equation allows quantification of H 2 O in silicate glasses that range in composition from basalt to rhyolite: wt% H 2 O = (ω·A 3450 /ρ) + b where ω = 550 ± 21, b = -0.19 ± 0.03, ρ = density, in g/cm 3 , and A 3450 is the ATR absorbance at 3450 cm -1 . The ATR micro-FTIR technique is less sensitive than transmission FTIR, but requires only a singly polished sample for quantitative results, thus minimizing time for sample preparation. Compared with specular reflectance, it is more sensitive and better suited for imaging of H 2 O variations in heterogeneous samples such as melt inclusions. One drawback is that the technique can damage fragile samples and we therefore recommend mounting of unknowns in epoxy prior to polishing. Our calibration should hold for any Ge ATR crystals with the same incident angle (31°). Use of a different crystal type or geometry would require measurement of several H 2 O-bearing standards to provide a crystal-specific calibration.

Ancient Roman syntheses of Al-tobermorite in a 2000-year-old concrete block submerged in the Bay of Pozzuoli (Baianus Sinus), near Naples, have unique aluminum-rich and silica-poor compositions relative to hydrothermal geological occurrences. In relict lime clasts, the crystals have calcium contents that are similar to ideal tobermorite, 33 to 35 wt%, but the low-silica contents, 39 to 40 wt%, reflect Al 3+ substitution for Si 4+ in Q 2 (1Al), Q 3 (1Al), and Q 3 (2 Al) tetrahedral chain and branching sites. The Al-tobermorite has a double silicate chain structure with long chain lengths in the b [020] crystallographic direction, and wide interlayer spacing, 11.49 Å. Na + and K + partially balance Al 3+ substitution for Si 4+ . Poorly crystalline calcium-aluminum-silicate-hydrate (C-A-S-H) cementitious binder in the dissolved perimeter of relict lime clasts has Ca/(Si+Al) = 0.79, nearly identical to the Al-tobermorite, but nanoscale heterogeneities with aluminum in both tetrahedral and octahedral coordination. The concrete is about 45 vol% glassy zeolitic tuff and 55 vol% hydrated lime-volcanic ash mortar; lime formed <10 wt% of the mix. Trace element studies confirm that the pyroclastic rock comes from Flegrean Fields volcanic district, as described in ancient Roman texts. An adiabatic thermal model of the 10 m 2 by 5.7 m thick Baianus Sinus breakwater from heat evolved through hydration of lime and formation of C-A-S-H suggests maximum temperatures of 85 to 97 °C. Cooling to seawater temperatures occurred in two years. These elevated temperatures and the mineralizing effects of seawater and alkali- and alumina-rich volcanic ash appear to be critical to Al-tobermorite crystallization. The long-term stability of the Al-tobermorite provides a valuable context to improve future syntheses in innovative concretes with advanced properties using volcanic pozzolans.

Nominally hydrous high-pressure silicate phases such as the superhydrous phase B are of considerable importance for the understanding of the water-cycle between the surface and the interior of the Earth. This study tackles the controversial issue of hydrogen positions in superhydrous phase B, a phase believed to be potentially stable in cold subducting ultramafic slabs. To investigate the nature of hydrogen incorporation into the structure of superhydrous phase B, neutron powder diffraction experiments have been performed. A structural model based on Pnn2 symmetry has been used for the analysis of the data, which is consistent with earlier spectroscopic studies. Application of Fourier synthesis with subsequent analyses of difference nuclear density maps and Rietveld fits reveal two distinct positions for deuterium, at 4c (0.194, 0.052, 0.596) and at 4c (0.186, 0.119, 0.388). This unambiguously shows that deuterium lies within large channels, which are formed between the edgeshared octahedra and vertex-linked tetrahedra along the b-axis of the structure. These results contrast with recent polarized single-crystal infrared spectroscopy studies where the position of one of two H atoms was estimated to lie close to the octahedral edge of an MgO 6 octahedron, thereby leaving the large structural channel empty.

Carlfrancisite, Mn 3 2+ (Mn 2+ ,Mg,Fe 3+ ,Al) 42 (As 3+ O 3 ) 2 (As 5+ O 4 ) 4 [(Si,As 5+ )O 4 ] 6 [(As 5+ ,Si)O 4 ] 2 (OH) 42 , is a new mineral from the Kombat mine, Otavi Valley, Namibia, and occurs as curved platy aggregates ~2 cm across on a matrix of Mn arsenates and oxides. It is yellowy orange to pale yellow with a very pale-yellow streak, translucent with a vitreous to opalescent luster, and does not fluoresce under ultraviolet light. Cleavage is micaceous on {001}, and no parting or twinning was observed. Mohs hardness is 3, and carlfrancisite is brittle with a hackly fracture. The calculated density is 3.620 g/ cm 3 . Optical properties were measured with a Bloss spindle stage for the wavelength 590 nm using a gel filter. The indices of refraction are e = 1.756, w = 1.758, and it is non-pleochroic. Carlfrancisite is trigonal, space group R3̄c, a = 8.2238(2), c = 205.113(6) Å, V = 12 013.5(4) Å 3 , Z = 6, c:a = 1:24.941. The seven strongest lines in the X-ray powder-diffraction pattern are as follows: d (Å), I, (hkl): 2.826, 100, (2̄ 2 44); 2.371, 88, (2̄ 3 40, 1̄ 3 41); 1.552, 84, (1̄ 5 0); 2.676, 63, (2̄ 3 7); 3.243, 54, (0 1 56, 1̄ 2 39); 4.107, 48, (1̄ 2 0); 2.918, 47, (0 2 40). Chemical analysis by electron microprobe and crystalstructure refinement gave As 2 O 5 13.07, As 2 O 3 3.18, P 2 O 5 0.50, V 2 O 5 0.74, SiO 2 8.96, Al 2 O 3 0.78, FeO 0.22, MnO 53.25, MgO 9.37, H 2 O(calc) 8.42, sum 98.49 wt%. The H 2 O content and the valence states of As were determined by crystal-structure analysis. The empirical formula is Mn 2+ 33.55 Mg 10.39 Fe 2+ 0.14 Al 0.68 As 3+ 1.44 (Si 6.67 P 0.32 V 5+ 0.37 As 5+ 5.08 )O 54 (OH) 42 on the basis of 96 anions with (OH) = 42 apfu. The structure of carlfrancisite is closely related to that of mcgovernite and turtmannite.

Apollo 12 sample 12032,366-19 is a 21.3 mg granite fragment that is distinct from any other lunar granite or felsite. It is composed of barian K-feldspar, quartz, sodic plagioclase, hedenbergite, fayalite, and ilmenite, with trace amounts of zirconolite, baddeleyite, apatite, and merrillite. The texture of 12032,366-19 is largely a micrographic intergrowth predominantly of K-feldspar and quartz and, to a lesser extent, plagioclase and quartz. Hedenbergite, fayalite, and ilmenite are present in minor but significant quantities-6.0, 3.1, and 1.7 wt%, respectively-and are scattered throughout the feldsparquartz intergrowths. Trace amounts of Zr-bearing phases are found including zirconolite (0.6 wt%) and baddeleyite (0.04 wt%). Incompatible trace-element concentrations are high in 12032,366-19, particularly the high-field-strength elements, e.g., Zr, Sm, and Th (1500, 25, and 61 μg/g, respectively). The chondrite-normalized, rare-earth-element concentrations form a “V-pattern” that is characteristic of other lunar granitic material. By modeling 12032,366-19 as a derivative from a KREEP-like parent melt, the composition and mineral assemblage can be obtained by extended fractional crystallization combined with separation of the low-density minerals plus trapped melt components prior to final solidification. However, this model cannot quantitatively account for the relatively sodic composition of the plagioclase (An 34-50 ) and requires that the starting melt has Na 2 O of 1.2-1.4 wt%, which is higher than most KREEP compositions. Formation of this assemblage by silicate-liquid immiscibility is neither required nor indicated by petrogenetic modeling.

The Koktokay No. 1 pegmatite is a Li-Cs-Ta-rich granitic pegmatite located in Altai, northwestern China. Zircon is present in most textural zones of this pegmatite and in its contact zone with surrounding metagabbro. Here we describe the detailed associations of zircon with other minerals, and the internal textures and chemistry of the zircons. Most zircon grains from the contact zone have relatively low HfO 2 (<9.4 wt%), whereas the bright rim of one such grain has high HfO 2 (18.0-18.7 wt%). Zircon grains from the aplite zone contain <9.6 wt% HfO 2 , although their thin and bright rims have higher HfO 2 (10.8-13.0 wt%). Most zircon grains from the quartz-muscovite zone have complex internal textures and have HfO 2 contents of <13.0 wt%. However, zircon grains from localized, nest-like, muscovite aggregates are highly enriched in HfO 2 (up to 36.1 wt%). Zircon (sl) from the cleavelandite-quartz-spodumene zone can be divided into two types based on petrography and chemistry. One group of zircons appears to be typical magmatic zircon and are greater than 100 μm in size, closely associated with albite, and have HfO 2 contents of 13.0-19.5 wt%. The second group of zircons is typically associated with muscovite and/or spodumene, is small in size (down to a few micrometers), and may exhibit zoning or alteration textures. The HfO 2 contents of this second zircon group are 19.8-58.9 wt%, indicating the presence of hafnian zircon to zirconian hafnon. Large HfO 2 content variations of up to 34.8 wt% were also observed within single zoned crystals. We suggest that the increase of HfO 2 in the magmatic zircon from 9.4 wt% in the contact zone to 19.5 wt% in the cleavelandite-quartz-spodumene zone mainly reflects fractional crystallization of pegmatite magma. However, the occurrence of hafnian zircon and hafnon in the cleavelandite-quartz-spodumene zone is likely related to coupled Li-F fluxing effects in the pegmatite magma.

The Archaean Sittampundi Layered Magmatic Complex (SLC) of south India is interpreted as a part of the oceanic crust that formed in a suprasubduction zone setting. The assemblage corundum + anorthite + amphibole (magnesiohornblende to tschermakite to pargasite) + clinozoisite (C 1 PACz) developed in highly calcic anorthosite of the SLC at the culmination of a ca. 2.46 Ga tectonothermal event. Changing physicochemical conditions during this early Paleoproterozoic (Siderian) event produced spinel + anorthite + second generation amphibole through destabilization of corundum + first generation amphibole. Spinel retains the shape of the corundum that it replaces (spinel pseudomorphing corundum, SCP) and is surrounded by a rind of plagioclase that separates spinel from the matrix amphibole. Development of the assemblage chlorite + clinozoisite + secondary corundum after spinel + anorthite + amphibole marks the terminal metamorphic event in this area. Mass-balance calculations on pseudomorphs and modeling of preserved reaction textures show that Na, Mg, Ca, and silica were mobile during the formation of the SCP. Al and Fe were mobile at the grain scale but remained immobile in the scale of a thin section. Activity adjusted partial petrogenetic grid in the systems Na 2 O-CaO-Al 2 O 3 -SiO 2 -H 2 O (NCASH) and Na 2 O-CaO-MgO-Al 2 O 3 -SiO 2 -H 2 O (NCMASH) along with the mineralogy of the rocks that were co-metamorphosed with the anorthosite show that (1) the assemblage C 1 PACz was formed during high-pressure metamorphism (11 ± 1 kbar and 725 ± 25 °C), (2) SCP and the plagioclase rind around it were formed during exhumation of these higher pressure rocks to lower pressure (7 ± 1 kbar, 675 ± 50 °C) along a steeply decompressive retrograde P-T path, and (3) post decompression cooling and hydration at near isobaric condition triggered the formation of the chlorite-clinozoisite-secondary corundum assemblage (6-8 kbar, <620 °C). The inferred P-T path is consistent with the view that the studied area that represents Archaean oceanic crust of SSZ affinity was subducted and subsequently exhumed during the early Paleoproterozoic orogeny.

The reactivity of ultramafic rocks under hydrothermal conditions controls chemical fluxes at the interface between the internal and external reservoirs of silicate planets. On Earth, hydration of ultramafic rocks is ubiquitous and operates from deep subduction zones to shallow lithospheric environments where it considerably affects the physical and chemical properties of rocks and can interact with the biosphere. This process also has key emerging societal implications, such as the production of hydrogen as a source of carbon-free energy. To date, the chemical model systems used to reproduce olivine hydrothermal alteration lead to the formation of serpentine with sluggish reaction rates. Here, we use in situ diamond-anvil cell experiments and show that the presence of aluminum in hydrothermal fluids increases the rate of olivine serpentinization by one to two orders of magnitude. Aluminum increases the solubility of olivine and enhances the precipitation of aluminous serpentine. After two days, olivine crystals were fully transformed to aluminous serpentine under conditions typical for natural hydrothermal environments, i.e., 200 and 300 °C, 200 MPa. This result motivates a re-evaluation of the natural rates of olivine serpentinization and of olivine hydrolysis in general in a wide range of settings. This discovery also opens the potential of the serpentinization reaction for industrial scale production of hydrogen at economically feasible timescales and temperature.

Beryl’s various coloring make it a sought-after and precious gemstone. Knowledge on the physical origin behind the various colorings is essential to differentiate artificial colorings from natural ones. The blue color of the variety aquamarine has been proposed to be due to charge transfer between adjacent Fe 3+ -Fe 2+ pairs on the Al site and its adjacent 6g interstitial position, respectively. The present work presents the first experimental confirmation of such an arrangement. Single-crystal electron paramagnetic resonance (EPR) spectra of a light blue beryl (Springbok, South Africa), before, and after annealing at 800 °C, have been measured at temperatures from 25 to 295 K and reveal two Fe 3+ -Fe 3+ pairs related to an axial Fe 3+ center at the effective g = ~2.00 as well as a subordinate rhombic Fe 3+ center at g = ~4.28. Powder EPR spectra show that the intensity of the axial Fe 3+ center increases after annealing from 400 to 800 °C but becomes constant after 800 °C, whereas the rhombic Fe 3+ center is not affected by annealing. One Fe 3+ -Fe 3+ pair is the same as the one investigated previously by Edgar and Hutton (1982) and arises from Fe 3+ ions at the two nearest Al sites along the c axis. The best-fit spin Hamiltonian parameters show that the second Fe 3+ -Fe 3+ pair is also oriented parallel to the c axis and has a separation of 2.4 Å, corresponding to Fe 3+ ions at an Al site and its nearest 6g interstitial position. The increased intensities of both Fe 3+ -Fe 3+ pairs after annealing suggest their formation from Fe 3+ -Fe 2+ and Fe 2+ -Fe 2+ precursors. Modeling of synchrotron Fe K-edge X-ray absorption spectra measured on the sample annealed at 1000 °C also shows occupancies of Fe 3+ at both the Al site and the 6g interstitial position. The assignment of the rhombic Fe 3+ center to the Be site remains tentative.

Hydrogen isotope partitioning (as H 2 O and D 2 O) between silicate-saturated aqueous fluid and water-saturated aluminosilicate melt has been determined with vibrational spectroscopy (Raman and infrared) in situ with the samples at high temperature and pressure by using a hydrothermal diamondanvil cell (HDAC) for sample containment. To assess the effects of pressure and, therefore, different silicate speciation in fluids and melts, on the D/H partitioning behavior, two pressure/temperature experimental trajectories (450-800 °C/155-754 MPa, and 450-800 °C/562-1271 MPa) were used. In these temperature and pressure ranges, the fluid/melt partition coefficients are temperature (and pressure) dependent with the average enthalpy change, △H = -6.6 ± 15 kJ/mol and -10.3 ± 1.1 kJ/mol for H 2 O and D 2 O, respectively. The △H-values for the lower-pressure trajectory (and, therefore, lower fluid density) were 15-20% higher than for the higher-pressure (and higher fluid density) trajectory. The (D/H) ratios of fluids and melts, (D/H) fluid and (D/H) melt , are also temperature dependent with a small negative DH for (D/H) fluid (average: -2.4 ± 0.8 kJ/mol) and a positive △H-value for (D/H) melt (2.3 ± 1.4 kJ/mol). The (D,H) exchange equilibrium between fluid and melt is also temperature (and pressure) dependent so that for the low-density P/T trajectory, the △H = -4.2 ± 0.6 kJ/mol, whereas for the higher-density trajectory, △H = -5.4 ± 0.7 kJ/mol. The difference between the H 2 O and D 2 O fluid/melt partition coefficients and the temperature- and pressure-dependent D/H fractionation behavior in and between hydrous silicate melts and silicate-saturated aqueous fluid in part is because pressure increases with increasing temperature in the HDAC experiments and the volume difference between fluid and melt differ for H 2 O and D 2 O. In addition, the silicate speciation in fluids and melts are temperature and pressure dependent, which also leads to significantly temperature- and pressuredependent D/H fractionation within and between silicate melts and fluids at high temperature and pressure. In the Earth’s deep crust and upper mantle, hydrogen isotope partitioning between condensed phases and aqueous fluid can differ substantially from that between condensed phases and pure H 2 O because the aqueous fluid in the Earth’s interior is a concentrated silicate solution wherein the silicate speciation affects the isotope partitioning.

Using density functional theory (DFT) calculations, the occurrences and correlation of gold (Au) and arsenic (As) in pyrite were studied, and the effect of As on the structural stability of Au in pyrite (FeS 2 ) was investigated. The calculated results show that Fe is not likely to be simply substituted with Au under normal circumstances. The presence of As is very conducive to incorporating Au into the pyrite interstitial lattice site along with substitution for the S site. It is predicted that a positive correlation exists between Au and As in pyrite and that higher As concentration facilitates the incorporation of Au in pyrite. Additionally, with increasing As content, Au sits on the Fe site and the Fe is repelled into the hole. The pyrite lattice expands with the incorporation of Au and As. Antibonding interactions are found between the Au, Fe, and As atoms. The reducibility of pyrite is greatly enhanced due to the presence of Au and As. The electronic structure calculations show that substituting Au and As for S atoms does not change the pyrite p-type property and that defect energy levels are present in the conduction band. However, with increasing As concentration, incorporating the interstitial site of Au causes a change from the p-type pyrite to an n-type pyrite, and defect energy levels are mainly located in the energy band gap. The interstitial site of Au causes the pyrite to be spin-polarized at a certain As content. In addition, strong interactions are found between Fe 3d and Au 6p orbitals and between Au 5d and As 4p orbitals.

Hydrated evaporite minerals have the ability to hold large amounts of H 2 O, making them a potential source of H 2 O in cold, low-PH 2 O environments such as the surface of Mars. Many of these hydrated evaporite minerals experience a reversible change in hydration state in response to changes in temperature (T) and relative humidity (RH). Such phases may thus have the potential to interact with the martian atmosphere on a daily or seasonal basis. The Na 2 Mg(SO 4 ) 2 ·nH 2 O system was previously thought to contain three hydrated phases: a decahydrate (n = 10), konyaite (n = 5), and blödite (n = 4). We examined this system using temperature- and RH-controlled X‑ray powder diffraction (XRD) methods, as well as temperature-controlled single-crystal X‑ray diffraction. When blödite was exposed to sub-freezing conditions, T ≤ -10 °C, a new phase was produced (n = 16, 52 wt%H 2 O). Similar low-temperature behavior has been documented in the MgSO 4 ·nH 2 O system, through the presence of meridianiite (Peterson et al. 2007). The hydration and dehydration behavior of phases in the Na 2 Mg(SO 4 ) 2 ·nH 2 O system was evaluated with powder XRD from -30 to >25 °C and from ∼99 to near 0% RH, and single-crystal XRD data were collected for the n = 16 phase at -120 °C. The 16-hydrate is triclinic, space group P1̄, with unit-cell parameters a = 6.5590(12), b = 6.6277(14), c = 14.441(3) Å, α = 87.456(15)°, β = 79.682(15)°, γ = 65.847(13)°, and a unit-cell volume of 563.3(2) Å 3 . The existence of this new phase at low temperatures, its high hydration state, and its ability to form reversibly from blödite all suggest that if phases in this system exist on the martian surface, they will participate in the Mars H 2 O cycle.

To use structural hydroxyl (OH) concentrations preserved in volcanic phenocrysts to constrain magmatic water contents prior to eruption, it is first necessary to understand the diffusive behavior of hydrogen in plagioclase. In this study, diffusion coefficients for a natural OH-bearing plagioclase feldspar (Ab 66 An 31 Or 3 ) are determined from a series of integrated loss heating experiments performed at 800-1000 °C and 1 atm under air, nitrogen gas, and a CO 2 -H 2 mixture at the FMQ oxygen buffer. Hydrogen diffusion is found to be isotropic within analytical error. Using a one-dimensional diffusive loss model for an infinite slab, the diffusion behavior for hydrogen in plagioclase is described by the diffusion parameters log D0 = -1.62 ± 0.31 (m 2 /s) and Ea = 266 ± 77 kJ/mol, and log D 0 = -0.97 ± 0.35 (m 2 /s) and Ea = 278 ± 90 kJ/mol for experiments only conducted under nitrogen gas. Nearly complete (83-97%) loss of OH from the andesine was achieved in 900 and 1000 °C heating series, except for the 900 °C FMQ buffer experiment in which only 64% of the total OH was lost after 21.6 days of cumulative heating. The diffusion rates of hydrogen in the plagioclase after 800-1000 °C are similar to interpolated diffusion rates for sodium diffusion in An 30 feldspar, implying that Na + and H + both diffuse via Frenkel defects involving the large cation sites and interstitial ions. The diffusion coefficient (D) values for hydrogen in plagioclase are lower than most reported diffusion data for hydrogen in nominally anhydrous minerals, and are most similar to D reported for pure forsterite, unaffected by iron redox reactions. Based on the hydrogen diffusion parameters in this study, a 1 mm spherical plagioclase phenocryst experiencing dehydration under lowered water activity during ascent and eruption at 800 °C retains 50% of its initial OH concentration after 34 days. At 900 and 1000 °C, a 1 mm phenocryst retains 50% of its initial OH concentration after only 1.3 days and 0.25 day, respectively. OH concentrations in plagioclase are therefore most indicative of magmatic water contents during the latest stages of ascent and eruption.

This study investigates the potential use of confocal micro-Raman spectroscopy for the quantification of CO 2 in geologically relevant glass compositions. A calibration is developed using a wide range of both natural and synthetic glasses that have CO 2 dissolved as carbonate (CO 3 2- ) in the concentration range from 0.2 to 16 wt%. Spectra were acquired in the 200 and 1350 cm -1 frequency region that includes the ν 1 Raman active vibration for carbonate at 1062-1092 cm -1 and the intensity of this peak is compared to various other peaks representing the aluminosilicate glass structure. The most precise and accurate calibration is found when carbonate peaks are compared to aluminosilicate spectral features in the high-frequency region (HF: 700-1200 cm -1 ), which can be simulated with several Gaussian peaks, directly related to different structural species in the glass. In some samples the “dissolved” CO 3 2- appears to have two different Raman bands, one sharper than the other. This may be consistent with previous suggestions that CO 3 2- has several structural environments in the glass, and is not related to any precipitation of crystalline carbonate from the melt during quenching. The calibration derived using the HF peaks appears linear for both the full range of glass composition considered and the range of CO 2 concentrations, even when multiple carbonate peaks are involved. We propose the following, compositionally independent linear equation to quantify the CO 2 content in glass with micro-Raman spectroscopy wt% CO 2 = 15.17 × CO 3 /HF where CO 3 /HF is the area ratio of the fitted ν 1 carbonate peak(s) at 1062-1092 cm -1 to the remaining area of the fitted aluminosilicate envelope from 700-1200 cm -1 . This is similar to the Raman calibration developed for water, but is complicated by the overlapping of these two fitted components. Using error propagation, we propose the calibration accuracy is better than ±0.4 wt% CO 2 for our data set. The ν 1 Raman peak position for carbonate is not constant and appears to be correlated with the density of the melt (or glass) in some way rather than the chemical composition.

Electronic spin transitions of iron in the Earth’s mantle minerals are of great interest to deep-Earth researchers because their effects on the physical and chemical properties of mantle minerals can significantly affect our understanding of the properties of the deep planet. Here we have studied the electronic spin states of iron in ringwoodite (Mg 0.75 Fe 0.25 ) 2 SiO 4 using synchrotron Mössbauer spectroscopy in a diamond-anvil cell up to 82 GPa. The starting samples were analyzed extensively using transmission and scanning electron microscopes to investigate nanoscale crystal chemistry and local iron distributions. Analyses of the synchrotron Mössbauer spectra at ambient conditions reveal two non-equivalent iron species, (Fe 2+ ) 1 and (Fe 2+ ) 2 , which can be attributed to octahedral and tetrahedral sites in the cubic spinel structure, respectively. High-pressure Mössbauer measurements show the disappearance of the hyperfine quadrupole splitting (QS) of the Fe 2+ ions in both sites at approximately 45-70 GPa, indicating an electronic high-spin (HS) to low-spin (LS) transition. The spin transition exhibits a continuous crossover nature over a pressure interval of ~25 GPa, and is reversible under decompression. Our results here provide the first experimental evidence for the occurrence of the spin transition in the spinel-structured ringwoodite, a mantle olivine polymorph, at high pressures.

Tuite, γ-Ca 3 (PO 4 ) 2 , is regarded as an important phosphate mineral in the deep mantle playing a crucial role as a host for rare earth elements, large ion lithophile elements, and phosphorus. In this study we report the thermoelastic properties of synthetic γ-Ca 3 (PO 4 ) 2 at simultaneously high pressures and temperatures of up to 35.4 GPa and 1300 K, respectively, as determined by means of in situ energydispersive X‑ray diffraction in a large-volume multi-anvil apparatus. The pressure-volume-temperature data obtained for γ-Ca 3 (PO 4 ) 2 were fitted by the high-temperature Birch-Murnaghan equation of state to yield V 2 = 447.4(4) Å 3 , K T0 = 100.8(18) GPa, K′ T0 = 5.74(13), (∂KT/∂T) P = -0.020(1) GPa/K, and α T = 3.26(18) × 10 -5 + 1.76(24) × 10 -8 T. In addition, fitting the present data to the Mie-Grüneisen-Debye equation of state gives γ 0 = 1.35(6), Θ 0 = 944(136) K, and q = 0.37(29). Based on the thermoelastic properties obtained in our study, the density profiles of γ-Ca 3 (PO 4 ) 2 tuite along typical cold and hot slab geotherms were calculated and are compared with those of the coexisting silicate minerals in subducting mid-ocean ridge basalt.

Atmospheric carbon is critical for maintaining the climate and life equilibrium on Earth. The concentration of this carbon is controlled by the deep carbon cycle, which is responsible for the billion year-scale evolution of the terrestrial carbon reservoirs of the planet. Understanding the crystal chemistry and physical properties of carbonates at mantle conditions is vital as they represent the main oxidized carbon-bearing phases in the Earth’s mantle. Here we present data on the crystal chemistry and physical properties of rhodochrosite at high pressure. Rhodochrosite (MnCO 3 ) exhibits a series of high-pressure transitions between 15 and 30 GPa and at 50 GPa at ambient temperature as observed by in situ Raman spectroscopy, X‑ray diffraction (XRD), and X‑ray emission spectroscopy (XES). A transition is observed to begin at 15 GPa and complete at 30 GPa, which may be due to several possibilities: modifications in the magnetic order, changes in the compression mechanism, and/or a structural transition resulting from disorder. We also observed a first-order phase transition of MnCO 3 at 50 GPa, which is not accompanied by any changes in the electronic spin state. These results highlight the unique behavior of MnCO 3 , which we found to be quite different from other common carbonates such as siderite, magnesite, and calcite.

The element selenium has become a considerable environmental concern due its accumulation in aquifers on the one hand and the high radiotoxicity of its long-lived isotope 79 Se on the other hand. Se(VI) is the most mobile of the various Se cations. This study deals with the interaction of Se(VI) with rock-forming minerals (carbonates) to better understand how to mitigate the potential environmental hazards of Se. The effect of Se(VI) on the cystallization of CaCO 3 at room temperature was studied using the silica hydrogel method. The CaCO 3 crystals obtained were characterized by X‑ray powder diffraction, scanning electron microscopy and electron microprobe. The presence of Se(VI) in the growth medium has a clear effect on the polymorph selection of CaCO 3 , promoting the formation of vaterite and inhibiting that of aragonite. Se(VI) also affects the characteristics of calcite crystals, which show progressively more elongated habits and smaller sizes with increasing Se(VI) concentration in the growth medium. The effect of Se(VI) on both the polymorphic crystallization of CaCO 3 and the characteristics of calcite crystals shows features strikingly similar to those of other tetrahedral anionic groups like S(VI) and Cr(VI). This similarity extends to the amount of Se incorporated into the structure of the different CaCO 3 polymorphs, with calcite having Se contents up to 1200 ppm, vaterite up to 500 ppm, and aragonite growing virtually Se-free. The role of Se(VI) on the crystallization of CaCO 3 is discussed taking into consideration the physicochemical conditions in the growth medium at nucleation, which were modeled using the PHREEQ code for low-temperature aqueous geochemistry. The possible effect of the incorporation of the Se(VI) on the relative stability and, by extension, on the solubility of CaCO 3 polymorphs is also discussed.

The stability of clay minerals is an important factor in assessing the durability of containment barriers for deep waste storage. In that context, the complete thermodynamic data set of three 2:1 ferro-magnesian clay minerals have been determined at 1 bar and from 2 to 520 K, using calorimetric methods. The studied clay samples were, respectively, the Na-saturated saponite Sap-Ca-1, Na 0.394 K 0.021 Ca 0.038 (Si 3.569 Al 0.397 Fe 3+ 0.034 )(Mg 2.948 Fe 2+ 0.021 Mn 0.001 )O 10 (OH) 2 , the Ca-saturated nontronite NAu-1, Ca 0.247 K 0.020 (Si 3.458 Al 0.542 )(Mg 0.066 Fe 3+ 1.688 Al 0.268 Ti 0.007 )O 10 (OH) 2 , and the Ca-saturated Santa Olalla vermiculite, Ca 0.445 (Si 2.778 Al 1.222 )(Al 0.192 Mg 2.468 Fe 3+ 0.226 Fe 2+ 0.028 Ti 0.018 Mn 0.007 )O 10 (OH) 2 . The standard enthalpies of formation were obtained by solution-reaction calorimetry at 298.15 K. The heat capacities were measured between 2 and 520 K, using low-temperature adiabatic calorimetry, heat-pulse calorimetry, and differential scanning calorimetry. The standard entropies and the Gibbs free energies of formation at 298.15 K have been calculated from these values. Finally, the equilibrium constants at 298.15 K have been determined. A comparison between these experimental data and estimated values obtained from prediction models available in the literature enabled the most usual calculation methods available to date to be assessed for each thermodynamic property.

Far-infrared spectroscopy and X‑ray powder diffraction Rietveld structure refinement for the hydrothermal synthetic muscovite series, (a) KAl 3 (Si 3-y Ge y )O 10 (OH,OD) 2 , (b) KGa 3 (Si 3-y Ge y )O 10 (OH,OD) 2 , and (c) K(Al 3-x Ga x )Ge 3 O 10 (OH,OD) 2 , where x = 0.0-3.0, y = 0.0-3.0, and the muscovite-tobelite series, (d) [K 1-A (NH 4 ,ND 4 ) A ]Al 3 Si 3 O 10 (OH,OD) 2 , where A = 0.0-1.0, indicate that there is a complete solid-solution in each series. In the 200-50 cm -1 far-infrared region, four kinds of bands are observed: two bands due to octahedral deformation coupled with OH deformational vibrations between 240 and 130 cm -1 , an in-plane tetrahedral torsional band between 175 and 130 cm -1 , an interlayer I-O inner stretching band, and an I-O outer stretching band. The weak and broad 140 cm -1 band is assigned to K-O inner stretching and the strong broad 110 cm -1 band to K-O outer stretching in muscovite. The broad 175 cm -1 band is (NH 4 /ND 4 )-O inner stretching and the 140 cm -1 broad strong band is (NH 4 /ND 4 )-O outer stretching in tobelite. With increasing Ga→Al substitution, the I-O inner and I-O outer stretching bands shift to lower frequency, while with increasing Ge→Si substitution, the I-O inner stretching band shifts to higher frequency; the I-O outer stretching bands do not change as a function of composition.

The partitioning of phosphorus between olivine and melt was measured by conducting partitioning experiments within the system Mg 2 SiO 4 -Ca 2 Al 2 Si 2 O 9 -NaAlSi 3 O 8 -Mg 3 (PO 4 ) 2 , using olivines crystallized with cooling rates in the range 1 to 10 °C/h. Partition coefficients, D P ol/melt , vary from 0.05 to 1.41 and are strongly influenced by melt composition, with high partition coefficients observed for more polymerized melts. Correlations between elemental abundances in the olivines demonstrate that phosphorus substitutes on a near one for one basis for Si, charge-balanced by Mg vacancies; no correlation between P and Al concentration in the olivine was observed. A complete understanding of the controls on D P ol/melt is required to model quantitatively the zoning of P in olivine that has recently been shown to be a common feature of igneous olivine crystals. The strong melt compositional dependence observed in this study implies that both changing concentrations of P in the melt during fractionation, and changing values of D P ol/melt can contribute to core-to-rim variations in P when the surface composition of a growing olivine crystal is in equilibrium with the melt. The common observation of zones in natural olivines where high P is correlated with high Al and Cr must be explained by processes other than equilibrium growth and, as suggested previously, such zones are probably related to solute trapping during episodes of rapid growth.

Traces of water in mantle minerals strongly influence mantle melting and viscosity that, in turn, governs large-scale processes like mantle convection, plate tectonics, and the stabilization of cratons. One way of estimating the mantle’s water content is by analyzing mantle xenoliths brought to the Earth’s surface. A major problem in estimating the mantle’s water budget from xenoliths arises from decompression-induced water loss during uplift. Mantle-derived xenoliths from numerous occurrences worldwide have been investigated with respect to water. However, little is known about water in the mantle beneath most parts of Europe and Asia. This study presents water contents for mantle olivine from Germany, Austria, Mongolia, and Nigeria and suggests a possibility to assess water loss. It also addresses the question whether or not water contents are related to olivine composition and/or the presence of coexisting amphibole. The highest water concentrations are present in olivine from the Eifel, Germany (up to 21 ppm H 2 O), whereas the Fichtelgebirge xenoliths, Germany, reveal the lowest contents (<1 ppm). All water-bearing olivines show three dominant infrared absorption bands: bands at 3572, 3525, and 3560 cm -1 and weaker bands at 3485, 3542, and 3597 cm -1 . The peaks at 3572 and 3525 cm -1 are ascribed to Ti-related substitutions of H. Additional peaks, related to H substitutions involving trivalent cations, occur in the 3300-3400 cm -1 range. However, their intensity does not correlate with the content of trivalent cations. The olivines show a pronounced correlation of Al + Cr and Ca implying that incorporation of Al and Cr is governed by pressure and temperature and primarily attributed to Tschermak’s substitution. This study confirms that a coupled substitution involving Ti is the most important mode of water storage in shallow upper mantle olivine. The Ti content and the fraction of water bound to “Ti defects” are related and support the substitution model Ti 4+ + 2H + = Mg 2+ + Si 4+ . Hence, the Ti content is a useful proxy to estimate the maximum amount of water incorporated by this substitution-providing a tool to approximate the degree of water loss. Five of the investigated olivines provide evidence for no or very little water loss. Their water content of 16-21 ppm is presumably typical for the depleted uppermost mantle. Twelve samples with <1-15 ppm may have lost between 36 and >80% of their original water. Olivine from amphibole-bearing spinel peridotite has relatively low water contents as well as low amounts of Ca, Al, Cr, Ti, and V. Particularly low Ca, Al, and Cr contents suggest fluid infiltration, amphibole formation, and re-equilibration of the whole assemblage at comparably low pressure and/or temperature and may explain the low water content of olivine. Infrared spectra with dominant peaks in the 3200-3300 cm -1 range (spectrum type E) are confined to olivine from amphibole-bearing peridotite.

The melting temperature of materials is an important thermodynamic property. Despite the importance of kaolinite, one of the most common clay minerals on the Earth’s surface, its thermal and melting behavior is poorly understood. We apply here the Z-method to determine the melting temperature (T m ) and the limit of superheating (TLS) of kaolinite. The T m is found at 1818 K (8.85 GPa), and T LS at 1971 K (6.8 GPa). The diffusion coefficient for all atoms has been calculated in a broad temperature range. The calculated characteristics and, in particular, their dependence on temperature have confirmed the solid-liquid transition and strongly support the calculated melting point. In addition, some computed quantities, such as the radial distribution function, coordination numbers and mean-square displacement, were used to confirm the liquid state of kaolinite from the melting temperature as well as at other temperatures in the liquid branch. The diffusion coefficient for different atoms has been calculated throughout the isochore. These quantities and in particular their evolution under temperature have confirmed the solid-liquid states of kaolinite and the presence of the melting point. The latter quantity constitutes the first ever melting simulation of a clay mineral with close agreement to the experimental one.

Darrellhenryite, Na(LiAl 2 )Al 6 (BO 3 ) 3 Si 6 O 18 (OH) 3 O, a new member of the tourmaline supergroup (related to the alkali-subgroup 4), is a new Li-bearing tourmaline species, which is closely related to elbaite through the substitution Y Al W 0.5 O 1 Y Li W - 0.5 (OH) -1 . It occurs in a complex (Li-bearing) petalite-subtype pegmatite with common lepidolite, Li-bearing tourmalines, and amblygonite at Nová Ves near Český Krumlov, southern Bohemia, Moldanubian Zone, Czech Republic. This zoned pegmatite dike cross-cuts a serpentinite body enclosed in leucocratic granulites. Pink darrellhenryite forms columnar crystals (sometimes in parallel arrangement) up to 3 cm long and up 2 cm thick, associated with albite (var. cleavelandite), minor quartz, K-feldspar, petalite, rare polylithionite, and locally rare pollucite. The optical properties and the single-crystal structure study (R1 = 0.019) of darrellhenryite are consistent with trigonal symmetry, w = 1.636(2), e = 1.619(2), birefringence: 0.017, space group R3m, a = 15.809(2), c = 7.089(1) Å, V = 1534.4(4) Å 3 , and Z = 3. The chemical analysis, in combination with the results from the single-crystal structure refinement, gives the formula X (Na 0.58 Ca 0.01 □ 0.41 ) 1.00 Y (Li 1.05 Al 1.95 ) 3.00 Z Al 6 (BO 3 ) 3 T (Si 6 O 18 ) V (OH) 3 W (O 0.66 F 0.34 ) 1.00 , which can be simplified to an ideal formula of Na(LiAl 2 ) Al 6 (BO 3 ) 3 Si 6 O 18 (OH) 3 O. The strongest lines of the powder pattern [d in Å (I, hkl)] are 4.180 (39, 211), 3.952 (54, 220), 3.431 (73, 012), 2.925 (100, 122), 2.555 (90, 051), 2.326 (42, 511), 2.029 (42, 223), 2.021 (42, 152), 1.901 (50, 342), 1.643 (49, 603). The density is D meas = 3.03(3) g/cm 3 , D calc = 3.038 g/ cm 3 . Darrellhenryite is considered to have crystallized in Li- and B-rich but F-moderate environments in complex pegmatites; no influence of higher activity of O on the darrellhenryite formation is implied from its mineral assemblage. The name is for Darrell J. Henry, Professor of Geology at the Louisiana State University, Baton Rouge, U.S.A., an expert on the mineralogy, petrology, crystal chemistry, and nomenclature of tourmaline-supergroup minerals.

Nizamoffite, ideally Mn 2+ Zn 2 (PO 4 ) 2 (H 2 O) 4 , is a new mineral from the Palermo No.1 pegmatite in North Groton, Grafton County, New Hampshire, U.S.A. It formed as the result of secondary alteration of primary triphylite and associated sphalerite. The crystals occur as colorless prisms up to 1 mm in length and 0.5 mm in diameter. The prisms are elongated and lightly striated parallel to [001] and exhibit the forms {100}, {010}, {230}, {011}, {031}, and {111}. The mineral is transparent and has a white streak, vitreous luster, Mohs hardness of about 3½, brittle tenacity, irregular fracture, and three cleavages: perfect on {010}, good on {100}, and fair on {001}. The measured and calculated densities are 3.00(1) and 2.961 g/cm 3 , respectively. It is optically biaxial (-), α = 1.580(1), β = 1.590(1), γ = 1.591(1) (white light), 2V meas = 28(1)°, and 2V calc = 35°. Nizamoffite exhibits strong dispersion, r < v. The optical orientation is X = a, Y = c, Z = b, and the mineral is nonpleochroic. Electron-microprobe analyses (average of 10), with H 2 O calculated on structural grounds, provided: CaO 0.20, MgO 0.61, MnO 15.80, ZnO 33.34, Fe 2 O 3 2.81, Al 2 O 3 0.10, P 2 O 5 32.05, H 2 O 15.95, total 100.23 wt%. The empirical formula (based on 12 O atoms) is: (Mn 2+ 0.99 Ca 0.02 ) Σ1.01 (Zn 1.82 Fe 3+ 0.12 Mg 0.07 ) Σ2.01 (P 1.00 O 4 ) 2 (H 1.96 O) 4 . The mineral dissolves readily in cold, dilute HCl. Nizamoffite is orthorhombic, Pnma, with the unit-cell parameters: a = 10.6530(4), b = 18.4781(13), c = 5.05845(15) Å, V = 995.74(8) Å 3 , and Z = 4. The eight strongest lines in the X‑ray powder diffraction pattern are [d obs in Å(I)(hkl)]: 9.27(71)(020); 4.62(37)(040,220); 4.43(24)(111); 3.424(52)(240,221); 2.873(100)(241); 2.644(36)(400,331); 2.540(33)(420,161,002); and 1.953(36)(281). Nizamoffite is isostructural with hopeite. The structure (R 1 = 1.7% for 1014 F o > 4σF) contains corner-sharing zigzag chains of ZnO 4 tetrahedra along [001]. The chains are connected by corner sharing with PO 4 tetrahedra to form sheets parallel to {010}. Three of the four PO 4 vertices link to ZnO 4 tetrahedra in the sheet, while the fourth links to an octahedron between the sheets. Each octahedron links to one tetrahedron from each of two adjacent sheets, thereby linking the sheets in the [010] direction. The octahedron contains Zn in hopeite and Mn in nizamoffite.

Mcalpineite has been found in the Gambatesa mine (eastern Liguria, Italy). It occurs in a quartz vein mainly as yellowish green earthy crusts consisting of poorly crystallized mcalpineite intergrown with an unidentified Cu-Te phase, as well as quite pure aggregates of well euhedral emerald green crystals (individually reaching up to 50 μm), associated with black fragments of paratellurite (TeO 2 ) and weissite (Cu 2-x Te). The chemical formula of this rare mineral, found at the McAlpine mine (typelocality; California, U.S.A.) and at the Centennial Eureka mine (Utah, U.S.A., co-type locality), was originally given Cu 3 TeO 6 ·H 2 O. X‑ray powder diffraction and selected-area electron diffraction data of mcalpineite are in good agreement with those of synthetic Cu 3 TeO 6 . In addition no evidence for structural OH group was detected by micro-Raman analysis carried out on samples from Gambatesa, Centennial Eureka, and McAlpine (co-type sample) mines. Taking into account structural, topological, and experimental evidence, the crystal structure and chemical composition of mcalpineite must be revised: the mineral crystallizes in the Ia3̄ space group and the correct chemical formula is Cu 3 TeO 6 .

Rossiantonite, ideally Al 3 (PO 4 )(SO 4 ) 2 (OH) 2 (H 2 O) 10 ·4H 2 O, triclinic (space group P1̄), a = 10.3410(5), b = 10.9600(5), c = 11.1446(5) Å, a = 86.985(2), b = 65.727(2), g = 75.064(2)°, V = 1110.5(1) Å 3 , Z = 2, is a new mineral from the Akopan-Dal Cin cave system in the Chimanta massif (Guyana Shield, Venezuela). The mineral occurs as small (≤0.15 mm) and transparent crystals in a white to slightly pink fine-grained sand, filling spaces between boulders of weathered quartz sandstone. Associated phases are gypsum, sanjuanite, rare alunite, quartz and micro-spherules of amorphous silica. Rossiantonite is colorless with a white streak and vitreous luster. The mineral is brittle with irregular to sub-conchoidal fracture and it shows a poorly developed cleavage. Rossiantonite is biaxial and not pleochroic, with mean refractive index of 1.504. The calculated density is 1.958 g/cm 3 . Electron microprobe analyses, with H 2 O measured by thermogravimetric analysis, provided the following empirical formula based on 28 O apfu: Al 2.96 Fe 0.03 P 1.01 S 2 H 30.02 O 28 . The five strongest lines in the X‑ray powder diffraction pattern, expressed as d (Å), I, (hkl) are: 4.647, 100, (210); 9.12, 56, (100); 4.006, 53, (220); 8.02, 40, (110); 7.12, 33, (011). The crystal structure, refined using 3550 unique reflections to R = 0.0292, is built of PO 4 and AlO 6 polyhedral rings, creating complex chains parallel b by sharing the OH-OH edge belonging to the Al(3) polyhedron. Three symmetrically independent Al sites can be identified, namely: Al(1), Al(2), and Al(3). Tetrahedral sites, occupied by P, share all their apexes with AlO 6 octahedra. Unshared octahedral apexes are occupied by water molecules. Four additional water molecules are placed in between the previously identified chains. Two oxygen tetrahedra, occupied by S atoms, are connected along the chains by means of weak hydrogen bonding. The rossiantonite structure shows similarities with minerals belonging to the sanjuanite-destinezite group.