Volume 98, Issue 11-12

“Roman concrete” was used as building material during Roman Imperial times for a great number of famous constructions with different functions. Well-known examples are aqueducts, for example the Pont du Gard in France and the Aqua Alexandrina in Rome, and numerous monuments such as the famous Coliseum and Pantheon in Rome. While visually less apparent today, ancient harbors also were an important part of constructions supporting the power of the Roman imperial system and were invaluable to control the Mediterranean Sea trade. The article “Unlocking the secrets of Altobermorite in Roman seawater concrete” by Jackson et al. (2013) describes the investigation of several extremely interesting samples drilled from 2000-yearold Roman maritime concretes in 11 harbors along the Mediterranean coast [the ROMACONS project 2002-2009 (Oleson et al. 2004)].

Proton diffusion in brucite was investigated by conducting hydrogen-deuterium (H-D) exchange experiments using multi-anvil high-pressure apparatuses at pressures from 3 to 15 GPa and temperatures in the range of 750-1050 K. The diffusion couple was composed of a natural proton-dominated brucite single crystal surrounded by synthesized D-doped brucite polycrystals. Micro-Raman spectroscopy was used to determine the diffusion profiles of the samples. The D/H diffusion profile across the boundary between single crystal and polycrystalline D-doped brucite showed an asymmetric pattern characterized by faster diffusion in aggregates. The D/H interdiffusion rate determined from the analysis of the single crystal side indicates that the interdiffusion rate increases with increasing H/D ratio. The H-D interdiffusion rate in the direction perpendicular to the c-axis is about 0.5 orders of magnitude higher than that in the direction parallel to the c-axis. At 3 GPa, the H-D interdiffusion coefficients [D(m 2 /s)] along and perpendicular to the c-axis of brucite at compositions of C OD norm = 0.2 in the single-crystal region were determined to be 3.30(±1.77) ×10− 11 exp[-48.2(±5.8) (kJ/mol)/ RT] and 1.43(±1.33) ×10 −9 exp[-67.5(±23.2) (kJ/mol)/RT], respectively. The H-D interdiffusion rate perpendicular to and along the c-axis increased about one order of magnitude by compression from 3 to 10 GPa, but the pressure enhancement became weaker above 10 GPa. From 10 to 15 GPa, there is almost no pressure dependence of proton diffusion for both directions. As pressure increases up to 10 GPa, enhancement of the proton migration is strongly correlated with the activation of the atomic interaction and decrease of O…O′ distance induced by compression. The positive pressure effect on the proton diffusion in brucite suggests that proton diffusion in higher-pressure hydrous phase becomes faster because of the shorter O…O′ distance.

Iron oxidation states and coordination numbers have been determined by micro-X‑ray absorption near edge spectroscopy (XANES) on the cores of a large group of microtektites from the Australasian, Ivory Coast, and North American (NA) tektite strewn field. The North American microtektites used in this study have been collected from five sites at different distances from the source crater; most have SiO 2 content between 70 and 80 wt%. Accurate analysis of the pre-edge peak energy position and integrated area allowed determination of Fe 3+ /(Fe 2+ +Fe 3+ ) ratios on all samples with an estimated error of ±0.05. Microtektites from the Australasian and Ivory Coast strewn fields show low values of the Fe 3+ /(Fe 2+ +Fe 3+ ) ratios, in fair agreement with tektites from the same strewn field. In contrast, microtektites from the North American strewn fields show a wide range of Fe 3+ /(Fe 2+ +Fe 3+ ) ratios from 0.02 to ca. 0.61. Comparison of Fe oxidation state data with chemical composition do not show any relation between Fe 3+ /(Fe 2+ +Fe 3+ ) ratios and Na, Ca, or K contents, thus suggesting that the high-Fe oxidation states are not the consequence of sea-water alteration. The difference between the Fe oxidation state of tektites and microtektites from the North American strewn fields suggests that some factors in the formation of the North American microtektites were different than for the North American tektites and for microtektites in the other strewn fields. Previous Fe oxidation state data on NA tektites strongly suggest that the wide range in Fe oxidation state we found on NA microtektites is not related to lateral heterogeneity of the target rocks. Despite a correlation between microtektite oxidation state and distance from the source crater, we maintain that Fe oxidation state is not related only to the microtektite droplet flight distance. This is in keeping with the fact that no significant variations in the Fe oxidation state have been found in microtektites from the Australasian strewn field, even for Australasian microtektites recovered in Antarctica. The Fe oxidation state in North American microtektites could be explained by interaction of melt droplets with a H 2 O-rich vapor plumes generated during the impact. These data point out that some difference must exist between the thermal histories of microtektites and tektites from the NA strewn field. Moreover, microtektites from the NA strewn field show also distinctively higher oxidation states than those from Ivory Coast or the Australasian strewn fields.

Vorlanite (CaU 6+ )O 4 [Fm3̅m, a = 5.3647(9) Å, V = 154.40(4) Å 3 , Z = 2] was found in larnite pyrometamorphic rocks of the Hatrurim formation at the Jabel Harmun locality, Judean Desert, Palestinian Autonomy. Vorlanite crystals from these larnite rocks are dark-gray with greenish hue in transmitted light. This color in transmitted light is in contrast to dark-red vorlanite [Fm3̅m, a = 5.3813(2) Å, V = 155.834(10)Å 3 , Z = 2] from the type locality Upper Chegem caldera, Northern Caucasus. Heating above 750 °C of dark-gray vorlanite from the Jabel Harmun, as well as dark-red vorlanite from Caucasus, led to formation of yellow trigonal uranate CaUO 4 . The unusual color of vorlanite from Jabel Harmun is assumed to be related to small impurities of tetravalent uranium.

Although Fe-sulfate minerals occur only rarely on Earth as alteration products of sulfidic basalts or in hydrothermal systems, multiple lines of evidence point to the importance of Fe- (and other) sulfate minerals on the surface of Mars. One such martian data set comes from the MIMOS II Mössbauer spectrometers on the Mars Exploration Rovers, which acquired hundreds of spectra from the martian surface at two locations. Interpretation of those spectra has been limited by the lack of a comprehensive set of laboratory analog spectra of the broad range of naturally occurring sulfate minerals. Accordingly, this study reports Mössbauer data of 98 samples representing 47 different sulfate mineral species, all containing six- or higher-coordinated Fe. The resultant Mössbauer parameters are related to the local polyhedral environment around the Fe cation in each mineral to explain variations in spectral characteristics. Results show that the size of the coordination polyhedron is the best predictor of quadrupole splitting, which increases with both octahedral volume and mean bond length. Species within groups of structurally similar minerals are shown to have comparable spectral peaks that generally fall within small ranges. Although coordination polyhedron geometry is not necessarily unique to any particular mineral species or group, Mössbauer data can be used to help constrain mineral identifications from martian spectra. The number of mineral species is large, but the range of crystal structures and hyperfine parameters may be small, so that in many cases, individual minerals cannot be uniquely fingerprinted. Examples would include quenstedtite, coquimbite, kornelite, and lausenite, which have indistinguishable spectra, as do apjohnite, bilinite, dietrichite, and römerite. Overlap of Mössbauer parameters is a particular complication for identification of Fe 3+ -rich phases because the range of Mössbauer parameters for Fe3+ in any coordination number is so small. Previous analyses of martian Mössbauer spectra reported the presence of jarosite (Klingelhöfer et al. 2004; Morris et al. 2004) and an unspecific ferric sulfate (Morris et al. 2008). New data presented here indicate that botryogen, metasideronatrite, and slavikite exhibit Mössbauer spectra similar to those attributed to jarosite at Meridiani Planum. Fibroferrite and rhomboclase have parameters similar to those observed at Arad Samra, and copiapite and parabutlerite could be present at Tyrone Mount Darwin and Berkner Island. Unique mineral identifications are generally not possible from Mössbauer data alone, particularly for paramagnetic phases, although combining Mössbauer results with other data sets enables a greater level of confidence in constraining mineralogy. This study provides a new expansive data set for future interpretation of iron sulfates on Mars

Single-crystal diffraction of jarosite, KFe 3 3+ (SO 4 ) 2 (OH) 6 , has been undertaken at low temperatures that proxy for martian surface conditions. Room-temperature data are consistent with literature data [a = 7.2913(5), c = 17.1744(17), and V = 790.72(11) in R3̅m], while the first low-temperature data for the mineral is presented (at 253, 213, 173, and 133 K). Data collections between 297 and 133 K show strongly anisotropic thermal expansion, with the c axis much more expandable than the a axis. Much of the anisotropy is due to strong distortion of the KO 12 polyhedron, which increases by 8% between 297 and 133 K. The data sets can aid in the identification of jarosite by X‑ray diffraction of martian soils using the Curiosity Rover’s CheMin instrument.

The content and transport of fluid phases such as water into the deep Earth is of great importance not only to correlate seismological models of the planet’s interior with mineralogical models, but also for the understanding of the evolution of the solid Earth as well as the Earth’s atmosphere. This study reports on the influence of water on the structural and physical properties of olivine, which is known to be the main constituent of the upper mantle. Two hydrous olivines of composition Fo 97 Fa 3 with water content of 4883 parts per million by weight (ppmw) (SZ0407A) and 8000 ppmw (SZ0407B) were synthesized at 1250 °C and 12 GPa. Single-crystal X‑ray diffraction was used to determine unit-cell parameters of SZ0407A and SZ0407B at pressures up to 7.1 GPa at room temperature. Synchrotron powder X‑ray diffraction and Raman scattering experiments were performed on sample SZ0407A in a diamond-anvil cell to 34 GPa at room temperature. For both samples, the compressibility is the largest along the b-axis and smallest along the a-axis. Using the compression (V/Vo) vs. pressure data for sample SZ0407A to 29 GPa, in conjunction with the third-order Birch-Murnaghan equation of state, we calculate the isothermal bulk modulus and its pressure derivative as K 0 = 119.2(12) GPa and K′o = 6.6(4). Single-crystal compression data for sample SZ0407A to 7 GPa give K o = 121.5(6) GPa and K′ o = 5.7(2); and for sample SZ0407B K o = 122.2(12) GPa and K′o = 6.2(4). High-pressure Raman spectra for SZ0407A up to 34 GPa show a continuous shift of all the observed bands to higher frequency with increasing pressure; there is no indication of any first-order phase transition. However, the Raman spectra indicate subtle discontinuous changes around 22 GPa, unobserved in previously reported studies on anhydrous olivines.

The configurational changes that occur with temperature, and how these vary with composition, affect the thermodynamic and transport properties of aluminosilicate melts but are not well understood. We present here high-resolution 27 Al and 17 O NMR data on several calcium aluminosilicate glasses along two silica isopleths crossing the metaluminous (SiO 2 -CaAl 2 O 4 ) join, prepared with varying quench rates and thus with fictive temperatures spanning approximately 100 K. In all compositions, five-coordinated aluminum increases with increasing fictive temperature. For glasses along the 60 mol% SiO 2 isopleth, NBO also increases with increasing fictive temperature; this is less obvious for the glasses along the 30 mol% SiO 2 isopleth. The data suggest the mixing of bridging oxygen contributes to the magnitude of the observed temperature effect on NBO and continue to suggest the existence of multiple mechanisms that generate NBO and V Al.

Temperature-dependent single-crystal X‑ray data were collected on gismondine (GIS) Ca 4 (Al 8 Si 8 O 32 )・18H 2 O from Rio Pian del Foco, Genova province, Italy, in steps of 25 °C up to 600 °C. At room temperature, gismondine has space group P2 1 /c with a = 10.0214(1), b = 10.5997(1), c = 9.8327(1) Å, b = 92.363(1)°, V = 1043.58(2) Å 3 . This structure remained stable up to 50 °C. The dehydration behavior then divided into two different pathways depending on the sample. In the more frequent path I, the LT P2 1 2 1 2 1 structure (phase B) Ca 4 (Al 8 Si 8 O 32 ) ・12H 2 O [a = 13.6801(8), b = 10.4670(6), c = 13.8667(9) Å, V = 1985.6(2) Å 3 ] formed at 75 °C. The orthorhombic structure has a doubled volume relative to the monoclinic room-temperature structure. At 150 °C the HT P2 1 2 1 2 1 structure (phase C) with 8 H 2 O pfu [a = 13.9014(12), b = 8.9469(8), c = 13.9697(14) Å, V = 1737.5(3) Å 3 ] occurred. This phase C has strongly compressed elliptical channels with Ca ions bonding to adjacent walls. At high temperature (300 °C), the quality of the diffraction pattern in path I further degraded and became inclusive. In path II the diffraction patterns were of considerably higher quality and at 75 °C the phase LT I2/a with 16 H 2 O pfu [a = 9.790(2), b = 10.437(2), c = 9.790(2) Å, b = 90.97(3)°, V = 1000.1(4) Å 3 ] formed, changing at 150 °C to HT I2/a [at 225 °C: a = 9.434(4), b = 9.044(2) c = 9.695(2), b = 89.04(1)°, V = 827.0(4) Å 3 ] with 4 H 2 O. Above 250 °C the HT I2/a structure topotactically transformed by a reconstructive mechanism to a triclinic C1 Ca feldspar structure [a = 8.152(5), b = 12.917(5), c = 7.126(4) Å, a = 93.26(3), b = 116.37(6), g = 88.72(5)°, V = 671.2(7) Å 3 ], which does not follow Loewenstein’s (1954) rule, as the framework has ordered corner-linked AlO 4 tetrahedra. As a consequence of the GIS to Ca feldspar transformation T-O bonds within four-membered rings break and reconnect to a new framework type. The HT I2/a structure with strongly twisted double crankshaft chains acts as precursor for the feldspar formation without an intermediate X‑ray amorphous phase usually found after complete dehydration of most natural zeolites. This study reports for the first time a low-temperature topotactic transformation from gismondine to Ca feldspar and explains the highly unusual occurrence of ordered Al-O-Al clusters in this feldspar structure.

We report new observations of a clathrate mineral, melanophlogite [46SiO 2 ⋅6(N 2 ,CO 2 )⋅2(CH 4 ,N 2 )], as part of a tuffaceous layer within a sample of the 2006 natrocarbonatite lava, whose composition reflects the typical magma erupted passively at Oldoinyo Lengai throughout the last ∼50 yr. The mineral has been identified by chemical composition, micro-X‑ray diffraction, and transmitted light optical characteristics. This is the first reported occurrence of a clathrate in an igneous carbonatite, and we conjecture that this mineral may be recognized elsewhere in alteration products of natrocarbonatite ash and in particular, combeite-bearing carbonatite lithologies. Specifically, melanophlogite is a rare polymorph of SiO 2 with guest molecules (e.g., CH 4 , CO 2 , SO 2 , N 2 , OH, Xe, and Kr) within a silicate framework. It occurs in an ash pellet-rich layer within the natrocarbonatite lava, as abundant groundmass crystals and as cores of individual ash pellets, with pseudocubic and pseudohexagonal habits, ranging from 50 to 100 μm in size, with numerous inclusions of nepheline laths aligned parallel to the crystal margins. It has high-C contents (up to 2.25 wt%) and CO 2 is considered to be the guest molecule due to crystallization within an alkaline carbonatitic-CO 2 -rich environment.

Changes in the mechanisms of formation and global distribution of phyllosilicate clay minerals through 4.567 Ga of planetary evolution in our solar system reflect evolving tectonic, geochemical, and biological processes. Clay minerals were absent prior to planetesimal formation ~4.6 billion years ago but today are abundant in all near-surface Earth environments. New clay mineral species and modes of clay mineral paragenesis occurred as a consequence of major events in Earth’s evolution-notably the formation of a mafic crust and oceans, the emergence of granite-rooted continents, the initiation of plate tectonics and subduction, the Great Oxidation Event, and the rise of the terrestrial biosphere. The changing character of clay minerals through time is thus an important part of Earth’s mineralogical history and exemplifies the principles of mineral evolution

In this study, solubility experiments on sodium tetraborate (NaB 4 O 7 ·10H 2 O, borax) are conducted in NaCl solutions up to 5.0 m at room temperature (22.5 ± 1.5 °C). In combination with solubility data of sodium tetraborate in Na 2 SO 4 solutions from the literature, the solubility constant (log K sp ) for sodium tetraborate for the following reaction Na 2 B 4 O 7 ·10H 2 O = 2Na+ + 4B(OH) 4 - + 2H + + H 2 O (l) is determined as -24.80 ± 0.10 based on the Pitzer model. In conjunction with the relevant Pitzer parameters, based on the above log Ksp for borax, and log b1 (0.25 ± 0.01) evaluated from the literature for the following complex formation reaction Na + + B(OH) 4 - = NaB(OH) 4 (aq) a thermodynamic model with high precision is established for the Na + -B(OH) 3 -Cl - -SO 4 2- system at high-ionic strengths up to saturation of halite (NaCl), mirabilite (Na 2 SO 4 ·10H 2 O), and thenardite (Na 2 SO 4 ). The model is validated by comparison of model predicted equilibrium compositions for the assemblages of borax alone, borax + halite, borax + mirabilite, borax + halite + thenardite, and borax + mirabilite + thenardite in the mixtures of NaCl+Na 2 SO 4 to ionic strengths of 8.0 m, with independent experimental values from the literature. The differences in concentrations of major ions, e.g., Na+, Cl - , and SO 4 2- , between model predicted and experimental values are generally <0.5%. The difference for total boron concentrations is <0.05 m with an error <25%. The revised thermodynamic model is applied to the potential recovery of borax from boronenriched brines via evaporation at 25 °C, using the two brines from China as examples. The reaction path calculations suggest that the brine from the Zhabei Salt Lake in Xizang (Tibet) Autonomous Region, is suitable to recovery of borax via evaporation at 25 °C, whereas the brine from the western Sichuan Province, although it is enriched in boron, is not suitable to extraction of boron as borax, but is suitable to extraction of potassium as sylvite, via evaporation at 25 °C.

Bone remodeling and tooth enamel maturation are biological processes that alter the physicochemical features of biominerals with time. However, although the ubiquity of bone remodeling is clear, why is well-crystallized bone mineral systematically replaced by immature nanocrystalline inorganic material? In enamel, a clear evolution is also seen from the first mineral formed during the secretory stage and its mature well-crystalline form, which then changes little in the adult tooth. This contribution provides the thermodynamic basis underlying these biological phenomena. We determined, for the first time, the energetics of biomimetic apatites corresponding to an increasing degree of maturation. Our data point out the progressive evolution of the enthalpy (ΔHf°) and free energy (ΔGf°) of formation toward more negative values upon maturation. Entropy contributions to ΔGf ° values remained small compared to enthalpy contributions. ΔHf° varied from -12 058.9 ± 12.2 to -12 771.0 ± 21.4 kJ/mol for maturation times increasing from 20 min to 3 weeks, approaching the value for stoichiometric hydroxyapatite, -13 431.0 ± 22.7 kJ/mol. Apatite thermodynamic stability increased as its composition moved toward stoichiometry. These findings imply diminishing aqueous solubility of calcium and phosphate ions as well as decreased surface reactivity. Such thermodynamically driven maturation is favorable for enamel maturation since this biomineral is intended to resist external aggressions such as contact with acids. In contrast, maintaining a metastable highly reactive and soluble form of apatite is essential to the effective participation of bone as a source of calcium and phosphate for homeostasis. Therefore our data strongly suggest that, far from being trivial, the intrinsic thermodynamic properties of apatite mineral represent a critical driving force for continuous bone remodeling, in contrast to current views favoring a purely biologically driven cycle. These thermodynamic data may prove helpful in other domains relating, for example, to apatite-based biomaterials development or in the field of (geo)microbiology.

Lizardite, being one of three serpentine minerals is of considerable interest in connection with understanding the geological processes occurring at subduction zones where serpentinized ocean floor is recycled into the Earth’s mantle. The crystal structure, elasticity, and vibrational properties of lizardite under pressure were determined using first-principles techniques. Above 10 GPa, a stable and a metastable structures were obtained. The hydrogen bond geometry of the stable structure indicates the disappearance of hydrogen bonds above 10 GPa, whereas the metastable structure does not show any noticeable change of the hydrogen bond strength throughout the pressure range up to 20 GPa. At 10 GPa, a very sudden softening of the elastic constants was observed for the stable structure, which is associated with a slight change in the compressibility of the c axis. This elastic softening causes a sudden reduction in the seismic velocities vP and vφ by about 16 and 24%, respectively. These velocities then steeply increase with further compression. Shear velocity vS, on the other hand, gradually decreases with pressure and then abruptly increases about 14% at 10 GPa. The calculated OH stretching frequencies also increase suddenly at -10 GPa. Previous Raman measurement reported that the highest OH stretching frequencies also increase steeply above 6 GPa. Therefore, there is a possibility that this elastic anomaly can be observed experimentally at about 6 GPa.

Understanding effects of non-hydrostatic pressure on phase transitions in minerals relevant to the Earth’s mantle is important to translate the observable seismic signals to not directly observable mineralogical models for the deep Earth. SiO 2 can occur as a free phase in subducting slabs, which contain sedimentary layers and/or mid-ocean-ridge basalts. In this study, we report on the effect of deviatoric strain on the pressure-induced phase transition in SiO 2 and its consequences on the seismic signal. The acoustic velocity in polycrystalline stishovite across the post-stishovite phase transition was measured by Brillouin scattering in the pure SiO 2 system at room temperature under deviatoric stress. High-pressure synchrotron X‑ray diffraction data were also collected at SPring-8. A linear fit to the symmetry-breaking strain values and the pressure of the transverse velocity minimum indicate a transition pressure between 25 and 35 GPa, which is about 20 GPa lower than that under hydrostatic conditions. The transverse velocity dropped by about 3% at around 25 GPa in this study. This is much smaller than the prediction from ab initio calculations that a transverse velocity reduces by ~60% at around 50 GPa under hydrostatic conditions. The results of the present study indicate that the deviatoric stress lowers the transition pressure and reduces the acoustic velocity change associated with the post stishovite phase transition. Sedimentary and mid ocean ridge basalt (MORB) layers in a subducting slab are likely sites for finding stishovite and its high-pressure polymorphs in the deep earth. Seismic observations of deep earthquakes occurring in subducting slabs indicate the existence of considerable stress in down-going slabs. This study suggests that nonhydrostatic deviatoric stress is one of the possible reasons for the absence of general seismic features that can be directly related to the poststishovite phase transition in subducting slabs at 1500 km depth. The phase transition of stishovite under deviatoric stress, which occurs at shallower depths, can affect the local seismic scattering structures and the rheological behavior of a subducting slab in the mid-lower mantle region.

The thermoelastic behavior and structural evolution of a natural levyne-Ca [(Ca 7.8 Na 2.2 K 1.1 ) Σ11.1 Al 20.0 Si 34.2 O 108 ⋅51.5H 2 O; R3m; a = 13.377(4) Å, c = 22.870(1) Å, V = 3544.1(3) Å 3 ] were studied by both T-resolved synchrotron X‑ray powder diffraction (SR-XRPD) between room temperature and 800 °C, and by conventional-source high-temperature single-crystal X‑ray diffraction (SC-XRD). Above 230 °C, water loss and reallocation of extraframework cations induce the straining and consequent breaking of T-O-T bridges in the D6R, with resulting migration of tetrahedral cations to new tetrahedral sites. The new tetrahedra share an edge with the previously occupied tetrahedra. This phenomenon gives rise to a new topology, which coexists to about 40%, with the original one. The new framework consists of a sequence of a novel zeolitic cage (described as a 20-hedron formed by fourteen 6mR and six 4mR) and two consecutive cancrinite cages along [0001]. This topology, which is reported in the database of the hypothetical zeolite structures as 166_2_293, belongs to the ABC-6 family and can be described by the following sequence of 6-rings: ABCBCACAB, to be compared with that of levyne AABCCABBC. In the new topology the extraframework cations are distributed over 3 new sites: one at the center of the 6mR ⊥ [0001] shared by the two cancrinite cages, one near the center of the 6mR ⊥ [0001] at the base of the new cage, and a last one in a 6mR window of the new cage. The 8mR bidimensional channel system originally present in levyne is therefore absent in the new topology and hence molecular diffusion is likely to be partially hindered in the dehydrated form. The phase transition is not completely reversible, at least in the short term, as only partial rehydration was demonstrated

X-ray diffraction Rietveld structure refinement and mid- and far-infrared spectral studies have been done on Ga-for-Al and Ge-for-Si substituted synthetic clintonites (Cln), CaMg 2 (Al 4-x Ga x )(Si 1-y Ge y ) O 10 (OH,OD) 2 (x = 0.0-4.0, y = 0.0-1.0). Rietveld analyses indicate that there is complete solid-solution in both the (Al 4-x Ga x )Si-, (Al 4-x Ga x )Ge-clintonite series. With increasing Ga-for-Al, the mean tetrahedral bond-length, <T-O>, and mean tetrahedral basal oxygen separation, < [4] O bas -O bas > increase, whereas the octahedral and interlayer parameters, the tetrahedral rotation angles (α), and the dimensional misfits (D) vary little. With increasing Ga-for-Al substitution in the Si-series the broad OH and OD stretching bands shift downward from 3607 to 3529 cm -1 and from 2671 to 2620 cm -1 , respectively. For the Ge-series samples, the OH and OD stretching bands shift downward from 3610 to 3523 cm -1 and from 2667 to 2611 cm -1 , respectively. According to the data of the curve fitting analysis, both the OH and OD-stretching bands are modeled by at least three broad [wider than 37 cm -1 of full-width at half height (FWHH)] I bands (M1M2M2 = MgMgAl 3+ /MgMgGa 3+ ) and a narrow (FWHH = 23-33 cm -1 ) and weak N band (M1M2M2 = MgMgMg) on the highest frequency side. In some samples, a very weak and broad V (one vacant M site) band at the lowest frequency region is observed. Tetrahedral Si-O, Al-O, and Ga-O stretching bands lie in fairly discrete regions, which are at 1030-830, 880-760, and 790-640 cm -1 , respectively. However, the band regions for both the tetrahedral Al-O and Ge-O stretching as well as the Ge-O and Ga-O stretching bands closely overlap each other. In the 720-500 cm -1 region, Si-O-Al, Al-O-Al, Si-O-Ga, Al-O-Ge, Al-O-Ga, Ge-O-Ga, and Ga-O-Ga deformational bands (tetrahedral-chain bending and “breathing” modes) are observed to overlap strongly. Around 300 and 200 cm -1 one observes the Ca-O inner and Ca-O outer stretching bands, respectively, which show a slight downward frequency shift (-7 cm -1 per Ga apfu) with Ga-for-Al substitution.

Calaverite, krennerite, and sylvanite are Au-Ag-tellurides with close compositions and related crystal structures. Previous experimental studies show that both calaverite and sylvanite transform to porous “mustard” gold under hydrothermal conditions; however the transformation of sylvanite follows a complex reaction path with several intermediary products, contrasting with the simple replacement of calaverite by gold. Here we report results of an experimental study of the transformation of krennerite, a phase with Ag contents intermediate between those of calaverite and sylvanite. Krennerite was replaced by Au-Ag alloy under all experimental conditions explored (160 to 220 °C; pH T ~ 3 and 9; varying availability of oxygen). No reaction was observed at the same temperature under dry conditions. The replacement was pseudomorphic and the resulting Au-Ag alloy was porous, consisting of worm-like aggregates with diameters ranging from 200 nm to 1 μm. The replacement of krennerite proceeds via an interface coupled dissolution-(re)precipitation (ICDR) reaction mechanism. Tellurium is lost to the bulk solution as Te(IV) complexes, and may precipitate away from the dissolution site. In contrast, Au-Ag alloy precipitates locally near the krennerite dissolution site. Overall, the hydrothermal alteration of krennerite is very similar to that of calaverite, but differs from the alteration of sylvanite, for which multi-step reaction paths led to complex products and textures under similar conditions. These striking differences are driven by the competition between solid-state reactions and ICDR reaction in sylvanite. This reflects the fact that a metastable, Ag-rich calaverite nucleates on sylvanite during the early steps of its dissolution, as a result of the close relationship between the structures of these two minerals and the enrichment in Au, Ag, and Te in solution at the reaction front. In contrast, for calaverite and krennerite, no such phase precipitates, and both minerals are transformed in a pseudomorphic manner into Au-Ag alloy.

By using a diamond-anvil cell (DAC) with laser heating technology, a cubic perovskite polymorph of SrSiO 3 has been synthesized at - 38 GPa and 1500-2000 K for the first time. The P-V data of this new phase give ambient temperate elastic constants of V 0 = 49.18(5) Å 3 , K0 = 211(3) GPa, respectively, when they are fitted against the Birch-Murnaghan equation of state with a fixed K0′ at 4. On decompression, the SrSiO 3 cubic perovskite phase becomes unstable at - 6.2 GPa and disappears completely at - 4.7 GPa. The transformed product can be considered as an amorphous phase with a minor amount of small sized crystals in the amorphous matrix. First principle calculations predicted structural properties of both the cubic and the six-layer-repeated hexagonal perovskite polymorphs of SrSiO 3 in good agreement with experimental results. The experimental and theoretical results indicate that the larger Sr 2+ cation can substitute the Ca 2+ cation and enter into the lattice of the cubic perovskite phase of CaSiO 3 at lower mantle conditions with only a small lattice strain. These results indicate that Sr can be hosted in cubic perovskite CaSiO 3 found as inclusions in diamonds originating from the lower mantle

This paper addresses the problem of magnetite nanoparticle size distributions in magnetotactic bacteria. The methods described in the paper can be used to determine the origin of natural magnetite nanoparticle samples. We analyzed 36 histograms related to bacterial, inorganic, and biomimetic nanoparticle sizes. Using statistical software we concluded that the size of the nanoparticles in cultured magnetotactic bacteria follows an extreme value distribution. Magnetite in uncultured samples can be treated as a two-component mixture containing extreme value and/or log-normally distributed nanoparticles. Analysis of the time-dependent formation of bacterial magnetite revealed that the magnetite size distribution transforms from the initial log-normal (young bacterial culture) through normal-like toward the extreme value distribution (evolved culture). It seems that at a certain moment during bacterial magnetite formation, the bacterial system starts to behave as a closed system. The closing of the system must be followed by another unknown process, because restriction of the nutrient supply into magnetosomes is insufficient for the generation of the extreme value distribution. Based on our analysis, approximately 50% of the magnetite particles in the martian meteorite ALH 84001 follow an extreme value distribution

The structures of K-rich feldspar, (K>Na)AlSi 3 O 8 , are currently described as “ideal” crystals with periodic average structures from Bragg diffraction maxima obtained by reciprocal-space techniques. Polymorphism is explained by variable substitutional disorder of framework Si and Al cations in tetrahedral T sites, and positional disorder of cavity alkali cations in a single M site. Here, highresolution magic angle spinning multinuclear magnetic resonance spectroscopy, leading to 29 Si, 27 Al, and 23Na spectra at 9.4 as well as 27 Al, 39 K, and 23 Na spectra at 19.6 T, has been used to investigate the “real” structures along the order-disorder series of K-feldspar crystals. The “ideal” and “real” structure coincides only in the perfectly long-range ordered triclinic end-member of the low-microcline structure. Long-range disordered structures (either with monoclinic or triclinic symmetry by X‑ray diffraction) show non-random disorder at the medium-range scale, triclinic-like distortions with four sets of T sites for framework atoms, two sets of M sites for alkali atoms, and Al-O-(K,Na) multi-site correlations by NMR spectroscopy. The K-feldspar structures can be described by a medium-range structure using the number of Al atoms per four-membered rings of tetrahedra, with “…-2-0-2-0-…” chains for microcline and orthoclase where the Al-occupancies t 1 O > t 2 m > t 2 O ≈ t1m, and with “…-1-1-1-1-…” chains for valencianite and sanidine, in which t 1 O > t 2 m ≈ t 2 O ≈ t 1 m. Framework cations respect Loewenstein’s rule (Al-O-Al avoidance), as well as some additional constraints of charge dispersion involving deficiency of Si atoms in Q 4 (4Si,0Al), (1Si,3Al), and (0Si,4Al) environments, constraints which are particularly strong in valencianite. These “real” structure features cannot be described by “ideal” structures owing to the lack of resolving power of the reciprocal-space techniques.

The structure and the polarized infrared absorption spectrum of OH-defects in wadsleyite (β-Mg 2 SiO 4 ) are studied, at 0 and 15 GPa, by first-principles calculations based on density functional theory (DFT). Four types of OH-defects are considered: fully protonated magnesium vacancies, fully protonated silicon vacancies, silicon vacancies compensated by a magnesium cation and two protons, and OH-defects associated with the migration of a silicon cation to a normally vacant site, as reported by Kudoh and Inoue (1999). The results suggest that the main absorption band constituted by a doublet (3326 and 3360 cm -1 ) corresponds to at least two types of OH-defects involving M3 vacancies with protonation of the O1-type O atoms along the O1...O4 edges. The main contribution of the less intense band at 3581 cm -1 is likely related to the partial protonation of a silicon vacancy (protonation of the O3-type oxygen) associated with the migration of the silicon cation to the Si2 site. This assignment is consistent with several experimental constraints: wavenumber and pleochroism of infrared OH-stretching bands, pressure-dependence of the band wavenumber, evidence from X‑ray diffraction of magnesium vacancies in M3 site, and increase of the b/a axial ratio with water content. The integrated absorption coefficients of the corresponding OH-defects are also calculated and thus complement the set of data obtained previously for forsterite and ringwoodite. Absorption coefficients of wadsleyite computed at 0 and 15 GPa indicate that for a precise quantification of the hydrogen content in in situ experiments, one must consider higher absorption coefficients than those determined at 0 GPa after quench. It is also shown that a single theoretical relation can account for the three Mg 2 SiO 4 polymorphs at 0 GPa: K int = 278.7 ± 18.1 (3810 ± 465 - x), where K int is the integrated molar absorption coefficient of the OH stretching modes and x is the average wavenumber in cm -1 . Absorption coefficients are significantly lower than the general calibrations, the use of which would lead to an underestimation of the water concentrations

Nanometric (<0.02, 0.02-0.05, 0.05-0.1, 0.1-0.2 mm) illite fractions were separated from Kbentonite samples from northwestern Georgia, and studied by X‑ray diffraction, oxygen and hydrogen isotope geochemistry, and K-Ar dated to more tightly constrain the tectono-thermal history of the Appalachian orogeny. Their XRD patterns are very similar for a given sample with respect to the peak shapes and positions. They are ordered illite-smectite mixed layers with only small variations in the relative proportions of illite and smectite interlayers. The illite crystal thickness distributions also are very homogeneous across the various size fractions of the same sample, but crystallite thickness varies from sample to sample. It can be concluded from the a-b2 diagram that illitization occurred in all fractions by simultaneous nucleation and crystal growth, except for one sample. In that sample, a period of growth without nucleation was detected on top of the nucleation and growth episode. The K-Ar ages organize into two isochrons, the first at 319.9 ± 2.0 Ma with an initial 40 Ar/ 36 Ar ratio of 271 ± 66 Ma, and the second at 284.9 ± 1.2 Ma with an initial 40 Ar/ 36 Ar ratio of 310 ± 44. One data point above the older isochron and three between the two isochrons suggest a detrital contamination for the former separate and a possible further generation of nanoparticles for the three others. The samples with the older crystallization age consist of illite and illite-rich mixed-layers, and those with the younger age contain smectite-rich mixed-layers without illite, or illite-enriched illite-smectite mixed-layers. The K-Ar ages fit the age trends published previously for similar K-bentonites with regional age patterns between 240 and 270 Ma in the southwestern region, between 270 and 300 Ma in the central zone and the southern Appalachians, and between 315 and 370 Ma in the northernmost. Each of the two generations of illite crystals yields very consistent δ 18 O (V-SMOW) values at 17 ± 1‰ for the older and at 21 ± 1‰ for the younger. If crystallization temperatures of the nanometric illite were between 100 and 200 °C, as suggested by microthermometric determinations, the hydrothermal fluids had δ 18 O values of 4 ± 1‰ in the Dalton district and of 8 ± 1‰ in the Lafayette, Trenton, and Dirtseller districts at 100 °C, and of 11 ± 1 and 15 ± 1‰ in the same locations at 200 °C, probably because the water-rock isotope exchanges at elevated temperature occurred in rock-dominated systems. The d18O of the fluids remained unchanged during local crystal growth, but varied depending on the geographic location of the samples and timing of illitization. The δD (V-SMOW) values of the different size fractions do not provide consistent information; they range from -70 to -45‰ for most nanometric and micrometric fractions (V-SMOW), but with no apparent coherent pattern. Nanometric illite-rich crystals from K-bentonite that underwent tectono-thermal alteration yield constant ages, constant clay mineralogy, constant crystallite size distributions for all of the nucleating and growing illite-type crystals of each sample, as well as constant δ 18 O values implying constant fluid chemistry, all pointing to geologically sudden crystallization

A detailed morphological, crystal-chemical, and structural characterization of erionite from the type locality of Durkee, Oregon, has been carried out by combining field emission scanning electron microscopy (FESEM) and laboratory parallel-beam transmission X‑ray powder diffraction (XRPD). According to the crystal-chemical formula (Na 5.38 K 1.99 Mg 0.24 )[Al 7.66 Si 28.34 O 72.09 ]·29.83H 2 O, the sample has been classified as erionite-Na. The Rietveld refinement has indicated that the extraframework cations are located at three Ca1, Ca2, and Ca3 sites, the first one containing all available Mg. Moreover, the absence of the additional K2 site found in both dehydrated erionite and erionite-K has been demonstrated for this erionite sample. Furthermore, our results revealed the absence of Fe and Ca although previous investigations have reported the presence of a variable content of both these elements in erionite samples from Durkee. This is relevant information because it is well known from amphibole asbestos that Fe 2+ has been claimed to be one of the causes of carcinogenesis by participating in Fenton chemistry and producing free radicals.

Phase relations in the system Na 2 CO 3 -CaCO 3 have been studied in the compositional range, X(Na 2 CO 3 ), from 100 to 10 mol%, at 6.0 GPa and 900-1400 °C. Below 1100 °C, the system has three intermediate compounds: Na 4 Ca(CO 3 ) 3 , Na 2 Ca 3 (CO 3 ) 4 , and Na 2 Ca 4 (CO 3 ) 5 . The Na 4 Ca(CO 3 ) 3 and Na 2 Ca 3 (CO 3 ) 4 compounds melt congruently slightly above 1200 and 1300 °C, respectively. The eutectics were established at 70 and 52 mol% near 1200 °C and at 21 mol% near 1300 °C. The Na 2 Ca 4 (CO 3 ) 5 compound decomposes to the Na 2 Ca 3 (CO 3 ) 4 + aragonite assembly at 1100 °C. Maximum solid solution of CaCO 3 in Na 2 CO 3 is 6-8 mol% at 1100-1300 °C. Melting of Na 2 CO 3 occurs between 1350 and 1400 °C. Na solubility in aragonite does not exceed the detection limit (<0.5 mol%). Aragonite remains a liquidus phase at 1300 and 1400 °C.

Phase relations in the Na 2 CO 3 -MgCO 3 system have been studied in high-pressure high-temperature (HPHT) multi-anvil experiments using graphite capsules at 6.0 ± 0.5 GPa pressures and 900-1400 °C temperatures. Sub-solidus assemblages are represented by Na 2 CO 3 +Na 2 Mg(CO 3 ) 2 and Na2Mg(CO 3 ) 2 +MgCO 3 , with the transition boundary near 50 mol% MgCO 3 in the system. The Na 2 CO 3 -Na 2 Mg(CO 3 ) 2 eutectic is established at 1200 °C and 29 mol% MgCO 3 . Melting of Na 2 CO 3 occurs between 1350 and 1400 °C. We propose that Na 2 Mg(CO 3 ) 2 disappears between 1200 and 1250 °C via congruent melting. Magnesite remains as a liquidus phase above 1300 °C. Measurable amounts of Mg in Na 2 CO 3 suggest an existence of MgCO 3 solid-solutions in Na 2 CO 3 at given experimental conditions. The maximum MgCO 3 solubility in Na-carbonate of about 9 mol% was established at 1100 and 1200 °C. The Na 2 CO 3 and Na 2 Mg(CO 3 ) 2 compounds have been studied using in situ X‑ray coupled with a DIA-type multi-anvil apparatus. The studies showed that eitelite is a stable polymorph of Na 2 Mg(CO 3 ) 2 at least up to 6.6 GPa and 1000 °C. In contrast, natrite, γ-Na 2 CO 3 , is not stable at high pressure and is replaced by β-Na 2 CO 3 . The latter was found to be stable at pressures up to 11.7 GPa at 27 °C and up to 15.2 GPa at 1200 °C and temperatures at least up to 800 °C at 2.5 GPa and up to 1000 °C at 6.4 GPa. The X‑ray and Raman study of recovered samples showed that, under ambient conditions, β-Na 2 CO 3 transforms back to γ-Na 2 CO 3 . Eitelite [Na 2 Mg(CO 3 ) 2 ] would be an important mineral controlling insipient melting in subducting slab and upwelling mantle. At 6 GPa, melting of the Na 2 Mg(CO 3 ) 2 +MgCO 3 assemblage can be initiated, either by heating to 1300 °C under “dry” conditions or at 900-1100 °C under hydrous conditions. Thus, the Na 2 Mg(CO 3 ) 2 could control the solidus temperature of the carbonated mantle under “dry” conditions and cause formation of the Na- and Mg-rich carbonatite melts similar to those found as inclusions in olivines from kimberlites and the deepest known mantle rock samples-sheared peridotite xenoliths (190-230 km depth).

In this paper we have presented a detailed response to Ertl et al. (2012a) who, in a paper in volume 97 (year 2012), pages 1402-1416, this journal, claim evidence for limitations of Fe 2+ and Mn 2+ occupancy at the Z site of the tourmaline structure. They also propose a model by which the <Z-O> distance of tourmaline varies as a function of its <Y-O> and <T-O> bond lengths. We have examined their conclusions and find that a different distribution of cations over the Y and Z sites gives better agreement with the extensive experimental information available. In fact, on the basis of crystalstructure refinements, Mössbauer spectroscopy, optical absorption spectroscopy, bond-valence theory, ionic radius concept and literature, the occurrence of Fe 2+ at the Z site of tourmaline is well supported. Conversely, existing experimental data does not provide indisputable evidence for the occurrence of Mn 2+ at the Z site. Despite this, there is no evidence for inductive effects of Y Mn 2+ on <Z-O>, and the proposed effects must be regarded as speculative. Statistical analysis shows that the <ZAl-O> average value is 1.906(2) Å, which is consistent with the observed values of <ZAl-O> at the 99% confidence limit (within 3σ) in tourmalines with the Z site fully occupied by Al. Consequently, the proposed inductive effect of <Y-O> and <T-O> on <Z-O> can be ruled out.

A spiked (with REE, V, Sc) martian basalt Yamato 980459 (Y98) composition was used to synthesize olivine, spinel, and pyroxene at 1200 °C at five oxygen fugacities: IW-1, IW, IW+1, IW+2, and QFM. These run products were analyzed by electron microprobe, ion microprobe, and X‑ray absorption nearedge spectroscopy to establish four oxybarometers based on vanadium partitioning behavior between the following pairs of phases: V spinel-melt, V/(Cr+Al) spinel-melt, olivine-melt, and spinel-olivine. The results for the spinel-melt, olivine-melt, and V/(Cr+Al) spinel-melt are applicable for the entire oxygen fugacity range while the spinel-olivine oxybarometer is only applicable between IW-1 and IW+1. The oxybarometer based on V partitioning between spinel-olivine is restricted to basalts that crystallized under low oxygen fugacities, some martian, all lunar, as well as samples from 4 Vesta. The true potential and power of the new spinel-olivine oxybarometer is that it does not require samples representative of a melt composition or samples with some remnant of quenched melt present. It just requires that the spinel-olivine pairs were in equilibrium when the partitioning of V occurred. We have applied the V spinel-olivine oxybarometer to the Y98 meteorite as a test of the method.