Editor’s Notes
Total Results: 1697
Volume 104 : June 2019 Issue
The condensation temperatures of the elements: A reappraisal
https://doi.org/10.2138/am-2019-6852CCBY
"Wood et al. (page 844) recalculated the temperatures at which the so-called ""moderately volatile elements"" such as Zn, In, Tl, Ga, Ag, Sb, Pb, and Cl, would condense from a gas of solar composition at 10-4 bar during formation of the solar system. The calculations highlighted three areas where currently available estimates of condensation temperature could be improved. The newly calculated 50% condensation temperatures are generally similar to or, because of the improvements, lower than those of Lodders (2003). Thus, this work provides a more accurate measure of the relative volatilities of the elements at the earliest stages of planetary formation."
Estimation of radiation damage in titanites using Raman spectroscopy
https://doi.org/10.2138/am-2019-6681
Heller et al. (page 857) explore the possibilities of estimating radiation damage (-dose) in titanites using Raman spectroscopy. Raman spectra of randomly oriented titanite fragments with known thermal history were related to their -dose, calculated from the concentration of -emitting elements. The intensity-weighted mean width of all Raman bands of a spectrum is independent from orientation and proves to be the most robust measure of -dose. This approach provides a pre-selection method to optimize the range of -doses of titanite crystals to be dated by (U-Th)/He thermochronology.
The effect of incorporated carbonate and sodium on the IR spectra of A- and AB-type carbonated apatites
https://doi.org/10.2138/am-2019-6800
Yoder et al. (page 869) have explored the IR spectra of carbonated calcium and strontium apatites that contain carbonate in the channel (A-type substitution) as well as in both the channel and in place of phosphate (B-type substitution). The results show that a correlation of the band position of the high frequency A-type carbonate band with weight percent carbonate exists for the calcium apatites, whereas a correlation of the band positions of both the low and high frequency B-type carbonate bands with carbonate weight percent occurs for the strontium apatites. On the other hand, correlations of band frequencies with sodium content are weaker than those for carbonate, even though carbonate and sodium are correlated with each other in the calcium apatites. This study also confirms previous conclusions about the distribution of A and B-type carbonate for most synthetic calcium apatites formed under a wide range of temperature and pressure conditions.
Re-configuration and interaction of hydrogen sites in olivine at high temperature and high pressure
https://doi.org/10.2138/am-2019-6921
Yang et al. (page 878) carried out in situ high-temperature and high-pressure IR spectroscopic investigations on hydrogen storage sites in the natural olivine and synthetic Fe-free forsterite. The results show that hydrogen does not transfer between storage sites with increasing temperature, but displays disordering at temperatures over 600 °C. In contrast, pressure can induce re-configuration of hydrogen storage sites corresponding to the 3610 and 3579 cm–1 bands. Hydrogen storage sites also exhibit disordering at high pressure. In addition, the dehydrogenation experiments of the natural olivine indicate interactions of hydrogen storage sites. Protons released from titanium-clinohumite defects move to pure Si vacancies, and also to Mg vacancies coupling with trivalent cations. This study is of importance to understand water distribution and its impact on the upper mantle.
The ascent of water-rich magma and decompression heating: A thermodynamic analysis
https://doi.org/10.2138/am-2019-6925
Glazner (page 890) conducted a thermodynamic analysis to reevaluate the ascent of water-rich magma and decompression heating. It has long been assumed that water-saturated magmas move into the subsolidus field and freeze upon ascent. However, this assumption ignores the considerable thermal energy released by crystallization. The new analysis shows that if magma ascent is treated as an adiabatic, reversible (isentropic) process then water-saturated magma can ascend without freezing, following the solidus to shallow depth and higher temperature as it undergoes modest crystallization and vapor exsolution. Decompression heating is an alternative to magma recharge for explaining pre-eruptive reheating seen in many volcanic systems and accounts for paradoxical growth of quartz during heating events. The viscosity increase that accompanies vapor exsolution as magma rises to shallow depth explains why silicic magmas tend to stop in the upper crust rather than erupting, producing the observed compositional dichotomy between plutonic and volcanic rocks.
High-pressure phase transitions of clinoenstatite
https://doi.org/10.2138/am-2019-6740
Lazarz et al. (page 897) conducted in situ single-crystal X-ray diffraction experiments to investigate high-pressure phase transitions of clinoenstatite (Mg2Si2O6): 1) from a low-pressure form (LPCEN, space group P21/c) to a high-pressure form (HPCEN, space group C2/c) at ~6 GPa; and 2) from HPCEN to a P21/c-structured polymorph (HPCEN2) at ~45 GPa (discovered in this work). High-pressure structure refinements of HPCEN were carried out to determine its P-V equation of state and structural evolution over an expanded pressure range relevant to pyroxene metatstability. The newly discovered HPCEN2 phase is related to the P21/c structure previously observed in diopside at 50 GPa and in clinoferrosilite at ~30-36 GPa.
Compressibility of two Na-rich clinopyroxenes: A synchrotron single-crystal X-ray diffraction study
https://doi.org/10.2138/am-2019-6658
Matrosova et al. (page 905) performed in situ high-pressure single-crystal X-ray diffraction experiments to determine compressibility of two synthetic Na-rich clinopyroxenes, a Na-Ti-pyroxene with formula (Na0.86Mg0.14)(Mg0.57Ti0.43)Si2O6 and a Na-pyroxene with composition (Na0.886Mg0.085Fe0.029)(Si0.442Mg0.390Fe0.168)Si2O6, up to 40 GPa. These phases were found to be monoclinic with the space group C2/c and exhibit KTo of 106.8(2) and 121.8(4) GPa, respectively. Na-Ti-pyroxene is more compressible than Fe-bearing Na-Mg-Si-pyroxene, likely because the FeO6 octahedron is significantly more rigid than MgO6 at high pressure. The formation of Na-rich pyroxenes in the deep mantle is related to crystallization of low-degree alkaline carbonate-silicate melts formed when the crust and mantle interact during the slab descent and its stagnation in the transition zone.
BOOK REVIEW
https://doi.org/10.2138/am-2019-B104612
This issue ends with a review by Hummer (page 914) on a textbook entitled “An Introduction to X-ray Physics, Optics, and Applications” by Carolyn MacDonald (2017), Cambridge University Press, 368 pp. The book presents a comprehensive, rigorous, but understandable explanation of X-ray physics and the many contexts in which this physics is useful in modern technologies. Hummer highly recommends this book to any student or researcher with an adequate background in physics who is seeking advanced knowledge of any system that utilizes X-rays.
Volume 104 : May 2019 Issue
Uptake and release of arsenic and antimony in alunite-jarosite and beudantite group minerals
https://doi.org/10.2138/am-2019-6591
Hudson-Edwards (p. 633) discusses research on the importance of alunite, jarosite, and beudantite group minerals as sinks for arsenic and antimony. These minerals can immobilize these elements and restrict their bioavailability in acidic, oxidizing environments. This ability to store arsenic and antimony can protect humans and other biota from their toxic effects. Aerobic and abiotic As release from alunite and natroalunite is limited, especially between pH 5 and 8. Release of As is also very limited in As-bearing jarosite, natrojarosite, and ammoniumjarosite at pH 8 due to the formation of secondary maghemite, goethite, hematite, and Fe arsenates that resorb the liberated As. Abiotic reductive dissolution of As-bearing jarosite at pH 4, 5.5, and 7 is likewise restricted by the formation of secondary green rust sulfate, goethite, and lepidocrocite that take up the As. Similar processes have been observed for the aerobic dissolution of Pb-As-jarosite (beudantite analog), with secondary Fe oxyhydroxides resorbing the released As at pH 8. Higher amounts of As are released, however, during microbial-driven jarosite dissolution. Natural jarosite has been found to contain up to 5.9 wt% Sb5+ substituting for Fe3+ in the B-site of the mineral structure. Sb(V) is not released from jarosite at pH 4 during abiotic reductive dissolution, but at pH 5.5 and 7, up to 75% of the mobilized Sb can be structurally incorporated into secondary green rust sulfate, lepidocrocite, or goethite. Further research is needed on the co-incorporation of As, Sb, and other ions in, and the uptake and release of Sb from, alunite, jarosite, and beudantite group minerals, the influence of microbes on these processes, and the long-term (>1 yr) stability of these minerals.
Trends in the discovery of new minerals over the last century
https://doi.org/10.2138/am-2019-6844
Barton (p. 641) examines the social, cultural, scientific, and technological factors that affected the rate and types of the 4,046 mineral discovery reports (roughly 3/4 of all known minerals) from 1917 to the present. The number of new minerals discovered per year was steady over time from 1917 to the early 1950s, when it began a rapid increase punctuated by spikes in 1962-1969, 1978-1982, and 2008-2016, the last of which is probably still ongoing. A detailed breakdown of the technological, geographic, institutional, and other characteristics of mineral discovery demonstrates that the availability of instrumentation for a particular analytical technique has a far larger impact on the rate of its uptake in mineral discovery than the technique's invention or computer-automation. Around 2/3 of all new mineral discoveries are found in samples associated with resource exploration and exploitation, with peralkaline intrusions and volcanic fumaroles as the next most productive source of new mineral discoveries. New mineral discovery is highly concentrated in specific laboratories or work groups Interestingly, although the number of analytical techniques continues to grow, the average number of methods used to characterize new minerals has not changed significantly since 1960, and about half of new mineral descriptions are made using roughly the minimum of analyses required for a new mineral to be recognized. Although some minerals have been discredited or redefined, most of those were due to changes in nomenclature and classification, and only five cases of fraudulent mineral discovery are known. This article presents the data underlying these analyses and discusses some possible reasons for the observed trends in the rate of new mineral discovery, as well as the implications for the history (and future) of mineralogy.
Origin of milky optical features in type IaB diamonds: Dislocations, nano-inclusions, and polycrystalline diamond
https://doi.org/10.2138/am-2019-6699
Gu et al. (p. 652) investigated enigmatic milky diamonds and revealed that dislocations, nano-inclusions, and polycrystalline textures are the possible origins of their appearance. Through application of cathodoluminescence (CL), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), Gu et al. suggest dislocation loops, nano-sized inclusions (negative crystals) and/or characteristic grain boundaries of the radiating fibrous crystals are the origins for the milky appearance of the type IaB diamonds studied.
Zeolite-group minerals in phonolite-hosted deposits of the Kaiserstuhl Volcanic Complex, Germany
https://doi.org/10.2138/am-2019-6831
Spürgin et al. (p. 659) present an unconventional zeolite deposit type and discuss the geological framework as an important factor for the generation of zeolite deposits hosted in subvolcanic alkaline rocks. This work is focused on the Miocene Kaiserstuhl Volcanic Complex, Germany, which shows that economic grades of zeolitization occur in phonolites intruded into water-rich, shallow marine sediments; whereas low degrees of zeolitization are found in phonolite intruded in dry, subaerial pyroclastic strata of the volcanic edifice. Pseudomorphic replacement textures indicate that zeolites formed from magmatic feldspathoid minerals. The common sequence from Ca-Na-rich zeolites (thomsonite, mesolite, gonnardite) towards pure Na-zeolites (natrolite, analcime) is the result of closed-system alteration. The late formation of Ca-K-rich chabazite in the latter phonolite is interpreted as open-system behavior with an influx of water in equilibrium with the leucite-bearing country rock, after the main alteration phase. This work concludes that zeolite deposits may not only be found in sheet-like, often very young tuffs but also in older rocks in a different geological context.
Melting curve minimum of barium carbonate BaCO3 near 5 GPa
https://doi.org/10.2138/am-2019-6891
Dong et al. (p. 671) measured the melting point of barium carbonate (BaCO3) at pressures up to 11 GPa using the ionic conductivity and platinum (Pt) sphere methods in a multi-anvil press. The melting point decreases with pressure from 2149 ± 50 K at 3 GPa to a minimum of 1849 K at 5.5 GPa, and then it increases with pressure to 2453 ± 50 K at 11 GPa. The negative slope of the BaCO3 melting curve between 3 and 5.5 GPa indicates that the liquid is denser than the solid within this pressure range. Synchrotron X-ray diffraction measurements in a laser-heated diamond-anvil cell showed that crystalline BaCO3 transformed from the aragonite structure (Pmcn) to the post-aragonite structure (Pmmn) at 6.3 GPa and 1026 K as well as 8 GPa and 1100 K, and the post-aragonite structure remained metastable upon quenching and only reverted back to the witherite structure upon pressure release. The local minimum near 5 GPa is attributed to the triple point where the melting curve of BaCO3 meets a phase transition to the denser post-aragonite structure (Pmmn). Local minima in the melting curves of alkaline earth carbonates would lead to incipient melting of carbonated rocks in Earth's mantle.
The effect of coordination changes on the bulk moduli of amorphous silicates: The SiO2-TiO2 system as a test case
https://doi.org/10.2138/am-2019-6729
Williams et al. (p. 679) demonstrate that packing changes in glasses have little influence on how glasses compact under pressure through their study of the elasticity of a sequence of SiO2-TiO2 glasses at high pressures and temperatures. The effect of changing Ti content on the bulk moduli of these glasses is monotonic, and no systematic effect of possible coordination changes is observed. In contrast, there is an apparent decrease in the pressure derivative of the bulk modulus above ~3 wt% TiO2. This change occurs at a similar composition to that at which a transition from predominantly 5-fold to 4-fold of Ti has been proposed to occur in these glasses. This shift in the pressure derivative of the bulk modulus is attributed to a stiffening of the equation of state for these glasses generated by the substitution of 5-fold Ti species relative to TiO4 units. These results provide rationales for the onset of coordination changes producing a minimal change in the equation of state of silicate melts/glasses, and for bulk moduli determined at ambient pressure producing relatively accurate silicate melt volumes even within liquids that have begun to undergo coordination changes. Thus, this study supports the general validity of the single equation of state formulations that describe the densities of silicate melts through the transition zone and shallow upper mantle.
Energetics of ethanol and carbon dioxide adsorption on anatase, rutile, and γ-alumina nanoparticles
https://doi.org/10.2138/am-2019-6797
Wu et al. (p. 686) explored the thermodynamics of interaction between nano oxides and small gas molecules by gas adsorption calorimetry to investigate the energetics of ethanol and carbon dioxide adsorbed on surfaces of nanoscale anatase, rutile, and γ-alumina particles. The measured zero-coverage adsorption enthalpies per mole of gas adsorbed are -97.7, -107.3, and -84.4 kJ/mol for C2H5OH on anatase, rutile, and γ-Al2O3, respectively. The corresponding values for CO2 adsorption are -61.6, -47.4 and -47.1 kJ/mol. The results indicate the ethanol adsorption is generally more exothermic than carbon dioxide and water adsorption. The isotherm and differential enthalpies show type II isotherms and step-wise patterns for ethanol adsorption in all three oxides. However, CO2 adsorption shows simple continuous isotherms and energetics that suggest dominantly physical adsorption occurred. The repeated adsorption cycle shows that ethanol adsorption on these nanoparticles is partially reversible at room temperature. This thermodynamic evidence indicates that ethanol and similar organics may protect mineral oxide surfaces from reaction with aqueous solutions, which may affect crystal growth, dissolution, and biomineralization.
The effect of oxidation on the mineralogy and magnetic properties of olivine
https://doi.org/10.2138/am-2019-6829
Knafeic et al. (p. 694) investigated the effect of olivine oxidation on its magnetic properties using a time series of 1 bar oxidation experiments at 600 °C and 900 °C. They found rapid olivine oxidation and alteration at both 600 and 900 °C, forming magnetite and hematite associated with a change from paramagnetic to ferromagnetic behavior after oxidation. Magnetite and hematite nucleated along dislocations and impurities in the crystal structure, along with surface coatings and within cracks in the crystals. Fresh, unaltered mantle xenoliths containing magnetite have been interpreted as having formed in cold tectonic regimes in the mantle, rather than through oxidation during or after the ascent. Mantle xenoliths rapidly ascend through the mantle with estimates of ascent of up to 90 km/hour (3 GPa/hour) based on the diffusion profile of water in mantle olivine. The rates correspond to xenoliths ascending through the mantle over hours and not days or weeks. Our results show that olivine oxidation and alteration can occur in days to weeks at 600°C and within minutes at 900 °C. Therefore, if the xenolithic material is transported to the surface in a cold magma (at temperatures less than or equal to 600 °C), then the time scale of ascent is likely not long enough for oxidation to cause magnetite formation or a ferromagnetic signature to occur. However, if the material is transported in a hot oxidized basaltic magma (with temperatures greater than or equal to 900 °C), then oxidation can cause magnetite formation and a ferromagnetic signature.
Phase, morphology, elemental composition, and formation mechanisms of biogenic and abiogenic Fe-Cu-sulfide nanoparticles: A comparative study on their occurrences under anoxic conditions
https://doi.org/10.2138/am-2019-6848
Mansor et al. (p. 703) investigated metal sulfide nanoparticles (NPs) because they are present in the environment and are important in controlling the availability of bio-essential and toxic metals in environmental remediation and in resource recovery. Characterizing the basic attributes of these NPs is the first step in understanding their behaviors in various processes. Experiments were performed in the presence and absence of the sulfate-reducer Desulfovibrio vulgaris to elucidate biological controls on NP formation. First, the single-metal end-member NPs were determined by precipitation in a solution containing either aqueous Fe(II) or Cu(II). Limited differences are observed between biogenic and abiogenic precipitates aged for up to one month; the Fe-only experiments resulted in 4-10 nm mackinawite (FeS) NPs that aggregate to form nanosheets up to ~1,000 nm in size, while the Cu-only experiments resulted in mixtures of covellite (CuS) NPs comprised of < 10 nm fine nanocrystals, 20-40 x 6-9 nm nanorods and ~ 30 nm nanoplates. The crystal sizes of biogenic mackinawite and covellite are respectively larger and smaller than their abiogenic counterparts, indicating a mineral-specific response to biological presence. Structural defects are observable in the fine nanocrystals and nanorods of covellite in both biogenic and abiogenic experiments, indicative of intrinsic NP instability and a formation mechanism via particle attachment. In contrast, covellite nanoplates are defect-free, indicating high stability and potentially rapid recrystallization following particle attachment. Mixed-metal sulfide NPs were precipitated at variable initial aqueous Fe-to-Cu ratios (2:1, 1:1 and 1:5). With increasing ratios of Fe-to-Cu, Fe-rich covellite, nukundamite (Cu5.5FeS6.5), chalcopyrite (CuFeS2), and Cu-rich mackinawite are formed. The Fe-rich covellite NPs are larger (100-200 nm) than covellite precipitated in the absence of Fe, indicating a role for Fe in promoting crystal growth. Chalcopyrite and nukundamite are formed through incorporation of Fe into precursor covellite NPs while retaining the original crystal morphology, as confirmed by doping a covellite suspension with aqueous Fe(II), resulting in the formation of chalcopyrite and nukundamite within days. Additionally, in the biological systems we observe the recrystallization of mackinawite to greigite (Fe3S4) after six months of incubation in the absence of Cu, and the selective formation of chalcopyrite and nukundamite at lower initial Fe-to-Cu ratios compared to abiotic systems. These observations are consistent with NP precipitation that ise influenced by the distinct (sub)micro-environments around bacterial cells. Comparative TEM analyses indicate that the synthetic NPs are morphologically similar to NPs identified in natural environments, opening ways to studying behaviors of natural NPs using experimental approaches.
Static compression of B2 KCl to 230 GPa and its P-V-T equation of state
https://doi.org/10.2138/am-2019-6779
Tateno et al. (p. 718) determined the pressure-volume-temperature (P-V-T) relationship of the B2 (CsCl-type) phase of KCl at 9-61 GPa at 1500-2600 K and up to 229 GPa at room temperature using synchrotron X-ray diffraction measurements in a laser-heated diamond-anvil cell (DAC). The nonhydrostatic stress conditions inside the sample chamber were critically evaluated based on the platinum pressure marker. With thermal annealing by laser after each pressure increment, the deviatoric stress was reduced to less than 1% of the sample pressure even at the multi-Mbar pressure range. The obtained P-V-T data were fitted to the Vinet equation of state with the Mie-Grüneisen-Debye model for thermal pressure. The thermal pressure of KCl was found to be as small as ~10 GPa even at 3000 K at any given volume, which is only half of that of common pressure markers (i.e. Pt, Au, or MgO). Such a low thermal pressure validates the use of a KCl pressure medium as a pressure marker at high temperatures.
Geochemical characteristics of lawsonite blueschists in tectonic mélange from the Tavşanlı Zone, Turkey: Potential constraints on the origin of Mediterranean potassium-rich magmatism
https://doi.org/10.2138/am-2019-6818
Wang et al. (p. 724) studied the petrology, mineralogy, and geochemistry of lawsonite blueschists from the Tavşanli zone in NW Turkey - one of the best-preserved blueschist terranes in the world. The blueschist samples contain lawsonite + sodic amphibole + phengite + chlorite + titanite + apatite ± aragonite ± quartz ± relict igneous pyroxene ± Mn-rich garnet and opaque phases. Lawsonite is a significant repository for Sr, Pb, Th, U, and REE, whereas phengite carries the most LILE; titanite hosts the highest Nb and Ta as well as considerable amounts of HFSE, and apatite strongly controls Sr. Two groups of blueschists with different origins were identified: one from enriched continent-derived terrigenous sediments and another from MORB-like submarine basalts. Lawsonite in blueschists with the enriched origin exhibits strong Th/La fractionation, raising the possibility of the involvement of blueschist facies mélange to explain the origin of Mediterranean potassium-rich magmatism, because similarly high Th/La ratios are also observed in the Mediterranean potassium-rich lavas. We propose that subduction-induced tectonic imbrication took place entirely at shallow depths (less than 80 km), giving rise to newly formed lithosphere where oceanic and continental crustal materials, sediments, strongly depleted peridotite blocks and metamorphic rocks are all imbricated together, and in which many of the compositional characteristics of the lawsonite blueschist are sequestered. Subsequent melting of the fertile and enriched components in this new lithosphere would result in the generation of potassium-rich post-collisional mafic magmas with diagnostic geochemical affinities.
Origin of vesuvianite-garnet veins in calc-silicate rocks from part of the Chotanagpur Granite Gneiss Complex, East Indian Shield: The quantitative P-T-XCO2 topology in parts of the system CaO-MgO-Al2O3-SiO2-H2O-CO2 (+Fe2O3, F)
https://doi.org/10.2138/am-2019-6811
Dey et al. (p. 744) studied a calc-silicate rock from part of the Chotanagpur Granite Gneiss Complex (CGGC), East India, that contains veins and patches of vesuvianite (F: 2.3-3.9 apfu, Fe3+: 1.7-2.1 apfu) and garnet (Gr71-80Alm12-17Adr1-9) proximal to amphibole-bearing quartzo-feldspathic pegmatitic veins. The vesuvianite-garnet veins are both parallel to, and cross-cutting, the gneissic banding of the host calc-silicate rock. Two contrasting mineralogical domains that are rich in garnet and vesuvianite respectively develop within the vesuvianite-garnet veins. Textural studies support the view that the garnet- and vesuvianite-rich domains preferentially develop in the clinopyroxene- and plagioclase-rich layers of the host calc-silicate rocks respectively. Some of the vesuvianite-rich domains of the veins develop the assemblage vesuvianite + quartz + calcite +anorthite (as a result of the reaction diopside + quartz + calcite + anorthite = vesuvianite) which was deemed metastable in the commonly used qualitative isobaric T-XCO2 topology in the system CaO-MgO-Al2O3-SiO2-H2O-CO2 (CMASV). Using an internally consistent thermodynamic database, quantitative petrogenetic grids in the P-T and isobaric T-XCO2 spaces were computed in the CMASV system. The influence of the non-CMASV components (e.g., Na, Fe3+, F) on the CMASV topologies are discussed using the published a-X relations of the minerals. This study shows topological inversion in the isobaric T-XCO2 space, which is primarily dependent upon the composition of the vesuvianite. The quantitative CMASV topologies presented in this study successfully explain the stabilities of the natural vesuvianite-bearing assemblages, including the paradoxical assemblage vesuvianite + quartz + calcite + anorthite. Application of the activity-corrected CMASV topology suggests that infiltration of F-bearing oxidizing aqueous fluids into the calc-silicate rocks developed the vesuvianite-garnet veins in the studied area. A genetic link between quartzo-feldspathic pegmatites and the vesuvianite-garnet veins seems plausible. This study demonstrates controls of topological inversion in the complex natural system, owing to which, certain mineral assemblages that are deemed metastable in one set of reaction geometries can develop in nature.
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