Published by De Gruyter

Volume 105 Issue 9

Issue of American Mineralogist

Contents
Journal Overview

MSA Centennial Review Paper

September 20, 2020

How American Mineralogist and the Mineralogical Society of America influenced a career in mineralogy, petrology, and plate pushing, and thoughts on mineralogy’s future role

W.G. Ernst

Page range: 1285-1296

Abstract

My geologic research began at Carleton College. I studied heavy minerals in some midcontinent orthoquartzites, publishing my very first paper in American Mineralogist in 1954. As a master’s candidate at the University of Minnesota, I investigated igneous differentiation in a diabase-granophyre sill of the Duluth Gabbro Complex. Later, in a Ph.D. program at Johns Hopkins University, I became Joe Boyd’s apprentice at the Geophysical Laboratory (GL), and for a time was phase-equilibrium god of the Na-amphiboles. Doctoral research earned me an offer of a UCLA assistant professorship as a mineralogist in 1960. There, I continued pursuing amphibole P-T stability relations in lab and field. My glaucophane phase equilibrium research would later be found to have instead crystallized Na-magnesiorichterite. However, amphibole research led me to map field occurrences of HP-LT (high P -low T ) blueschists of the Franciscan Complex. Thus, when plate tectonics emerged in the late 1960s, I was deep in the subduction zone. My recent studies focused on the petrology and geochemistry of oceanic crustal rocks, Californian calc-alkaline arcs, and coesite ± microdiamond-bearing crustal margin rocks in various parts of Eurasia. Other works treated global mineral resources and population, mineralogy and human health, and early Earth petrotectonic evolution. I tried to work on important problems, but mainly studied topics that fired my interest. For the future, I see the existential challenge facing humanity and the biosphere as the imperative to stop our overdrafting of mineral resources. This will require reaching a dynamic equilibrium between the use and replenishment of near-surface resources (i.e., nutrients) essential for life. Earth scientists are planetary stewards, so we must lead the way forward in life-supporting mineral usage, recycling, substitution, and dematerialization. In any event, sustainable development will soon return to the Earth’s Critical Zone of life because Mother Nature—the ruling terrestrial economist—abhors long-term overdrafting of resources Recently, a series of profound calamities have overwhelmed the World—the coronavirus pandemic, disruption of the global economy, and near-universal condemnation of the widespread, systemic abrogation of human rights/racial justice. Comparable challenges have emerged episodically ever since the rise of civilization. Such problems have been addressed over the millennia with varying degrees of success. However, human efforts have never achieved dynamic environmental equilibrium between consumption of Earth resources and rates of recharge. Sustainable development remains our long-term, existential threat. .

September 20, 2020

Petrographic and spectral study of hydrothermal mineralization in drill core from Hawaii: A potential analog to alteration in the martian subsurface

Wendy M. Calvin, Nicole Lautze, Joe Moore, Donald Thomas, Eric Haskins, Brandon P. Rasmussen

Page range: 1297-1305

Abstract

Continuous rock core was collected for 1764 m (5786′) on the Pohakuloa Army Training base near the center of the big island of Hawaii. The core traverses basaltic lava flows from the volcano’s shield-building phase, and perched aquifers and higher temperature groundwaters were encountered. The collected samples record water-rock interactions of basaltic materials in a setting that may be a model for groundwater interactions on Mars. We collected visible and infrared point spectra of materials in the lowest portion of the core, where alteration was noted to become more prominent. We identified three types of phyllosilicate spectral signatures and three types of zeolites. The phyllosilicates show similarity to those identified on Mars using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Based on the field survey, 25 depths were selected for sampling and petrographic analysis of thin sections. The spectral data and thin section work have a strong agreement in the types of materials identified by the two different techniques. Both the spectral and petrographic data indicate low to moderate temperature geothermal alteration occurred in the lower half of the core. The field spectra are a useful reconnaissance tool for selecting mineralogic diversity for subsequent higher resolution and more time-consuming laboratory analysis.

September 20, 2020

Characterizing low-temperature aqueous alteration of Mars-analog basalts from Mauna Kea at multiple scales

Brandon P. Rasmussen, Wendy M. Calvin, Bethany L. Ehlmann, Thomas F. Bristow, Nicole Lautze, Abigail A. Fraeman, Joel W. DesOrmeau

Page range: 1306-1316

Abstract

We performed a multi-scale characterization of aqueous alteration of Mars analog basaltic rock from a Mauna Kea drill core using high-resolution visible and short-wave infrared (VIS-SWIR) spectral imaging, scanning electron microscopy, X‑ray diffraction, and point VIS-SWIR spectra. Several types of smectites, zeolites, and primary minerals were identified. Mineral classes were mapped in cut sections extracted from the drill core and used to represent the range of alteration products seen in field data collected over 1000 m depth (Calvin et al. 2020). Ten distinct spectral end-members identified in the cut sections were used to map the field point spectra. Trioctahedral Fe- and Mg-rich smectites were present toward the top of the zone of analysis (972 m below the surface) and increased in abundance toward the bottom of the drill core (1763 m depth). The mineralogy demonstrates a general trend of discontinuous alteration that increases in intensity with depth, with less pervasive phyllosilicate alteration at the top, several zones of different mixtures of zeolites toward the center, followed by more abundant phyllosilicates in the lowest sections. Distinctly absent are Fe-Mg phyllosilicates other than smectites, as well as carbonates, sulfates, and Al phyllosilicates such as kaolinite or illite. Furthermore, hematite was only detected in two of 24 samples. The suite of assemblages points to aqueous alteration at low-to-moderate temperatures at neutral to basic pH in low-oxygen conditions, with little evidence of extensive surface interaction, presenting a possible analog for an early Mars subsurface environment. We also present a library of VIS-SWIR spectra of the analyzed cut sections, including both spatial averages (i.e., unweighted linear mixtures) of spectral images of each cut section and single point spectra of the cut sections. This will allow for consideration of nonlinear mixing effects in point spectra of these assemblages from natural surfaces in future terrestrial or planetary work.

Open Access September 20, 2020

Archean to Paleoproterozoic seawater halogen ratios recorded by fluid inclusions in chert and hydrothermal quartz

Ray Burgess, Sarah L. Goldsmith, Hirochika Sumino, Jamie D. Gilmour, Bernard Marty, Magali Pujol, Kurt O. Konhauser

Page range: 1317-1325

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Abstract

Past changes in the halogen composition of seawater are anticipated based on the differing behavior of chlorine and bromine that are strongly partitioned into seawater, relative to iodine, which is extremely depleted in modern seawater and enriched in marine sediments due to biological uptake. Here we assess the use of chert, a chemical sediment that precipitated throughout the Precambrian, as a proxy for halide ratios in ancient seawater. We determine a set of criteria that can be used to assess the primary nature of halogens and show that ancient seawater Br/Cl and I/Cl ratios can be resolved in chert samples from the 2.5 Ga Dales Gorge Member of the Brockman Banded Iron Formation, Hamersley Group, Western Australia. The values determined of Br/Cl ~2 × 10 -3 M and I/Cl ~30 × 10 -6 M are comparable to fluid inclusions in hydrothermal quartz from the 3.5 Ga North Pole area, Pilbara Craton, Western Australia, that were the subject of previous reconstructions of ancient ocean salinity and atmospheric isotopic composition. While the similar Br/Cl and I/Cl values indicate no substantial change in the ocean halide system over the interval 2.5–3.5Ga, compared to modern seawater, the ancient ocean was enriched in Br and I relative to Cl. The I/Cl value is intermediate between bulk Earth (assumed chondritic) and the modern seawater ratio, which can be explained by a smaller organic reservoir because this is the major control on marine iodine at the present day. Br/Cl ratios are about 30% higher than both modern seawater and contemporary seafloor hydrothermal systems, perhaps indicating a stronger mantle buffering of seawater halogens during the Archean.

September 20, 2020

Metasomatism-controlled hydrogen distribution in the Spitsbergen upper mantle

Wenting Tang, Hejiu Hui, Dmitri A. Ionov, Wei Chen, Lisha Zhang, Yongjiang Xu

Page range: 1326-1341

Abstract

Hydrogen concentrations in minerals of peridotite xenoliths in alkali basaltic rocks from Quaternary volcanoes in northwest Spitsbergen were measured using polarized Fourier transform infrared spectroscopy (FTIR) to trace the effects of geologic processes on hydrogen distribution in the continental lithospheric mantle. The mineral grains show hydrogen profiles with lower concentrations at rims suggesting diffusive hydrogen loss during the entrapment and transport of the xenoliths in magma. However, hydrogen concentrations in the centers of the grains are uniform and appear to represent hydrogen abundances in the Spitsbergen upper mantle. The olivine, orthopyroxene, and clinopyroxene contain 1–10, 130–290, and 350–560 ppm H 2 O, respectively. Hydrogen abundances away from metasomatic melt conduits recorded by Type 1 xenoliths are correlated with the concentrations of incompatible trace elements, indicating that hydrogen distribution is related to mantle metasomatism. By contrast, hydrogen near the melt conduits, recorded by Type 2 xenoliths, shows no regular correlations with incompatible trace elements (except Nb in clinopyroxene) and may be affected by fractional crystallization of amphibole in the conduits. Hydrogen contents decrease away from the melt conduits and are controlled by the interaction between the depleted host mantle and percolating metasomatic melts. Therefore, the metasomatic melt could have variably hydrated the Spitsbergen upper mantle via different processes. The H 2 O/Ce ratios of the melt in equilibrium with clinopyroxene near the metasomatic melt conduits range from 93 to 218, i.e., within the oceanic island basalt (OIB) range. This is consistent with that the metasomatic melt could have been derived from OIB-type sources evidenced by the Sr-Nd isotope compositions of the xenoliths.

September 20, 2020

Phase transformation of hydrous ringwoodite to the lower-mantle phases and the formation of dense hydrous silica

Huawei Chen, Kurt Leinenweber, Vitali Prakapenka, Martin Kunz, Hans A. Bechtel, Zhenxian Liu, Sang-Heon Shim

Page range: 1342-1348

Abstract

To understand the effects of H 2 O on the mineral phases forming under the pressure-temperature conditions of the lower mantle, we have conducted laser-heated diamond-anvil cell experiments on hydrous ringwoodite (Mg 2 SiO 4 with 1.1 wt% H 2 O) at pressures between 29 and 59 GPa and temperatures between 1200 and 2400 K. Our results show that hydrous ringwoodite (hRw) converts to crystalline dense hydrous silica, stishovite (Stv) or CaCl 2 -type SiO 2 (mStv), containing 1 wt% H 2 O together with Brd and MgO at the pressure-temperature conditions expected for shallow lower-mantle depths between approximately 660 to 1600 km. Considering the lack of sign for melting in our experiments, our preferred interpretation of the observation is that Brd partially breaks down to dense hydrous silica and periclase (Pc), forming the phase assembly Brd + Pc + Stv. The results may provide an explanation for the enigmatic coexistence of Stv and Fp inclusions in lower-mantle diamonds.

September 20, 2020

Density and sound velocity of liquid Fe-S alloys at Earth’s outer core P-T conditions

Jie Fu, Lingzhi Cao, Xiangmei Duan, Anatoly B. Belonoshko

Page range: 1349-1354

Abstract

Pressure-temperature-volume ( P - T - V ) data on liquid iron-sulfur (Fe-S) alloys at the Earth’s outer core conditions (~136 to 330 GPa, ~4000 to 7000 K) have been obtained by first-principles molecular dynamics simulations. We developed a thermal equation of state (EoS) composed of Murnaghan and Mie-Grüneisen-Debye expressions for liquid Fe-S alloys. The density and sound velocity are calculated and compared with Preliminary Reference Earth Model (PREM) to constrain the S concentration in the outer core. Since the temperature at the inner core boundary ( T ICB ) has not been measured precisely (4850~7100 K), we deduce that the S concentration ranges from 10~14 wt% assuming S is the only light element. Our results also show that Fe-S alloys cannot satisfy the seismological density and sound velocity simultaneously and thus S element is not the only light element. Considering the geophysical and geochemical constraints, we propose that the outer core contains no more than 3.5 wt% S, 2.5 wt% O, or 3.8 wt% Si. In addition, the developed thermal EoS can be utilized to calculate the thermal properties of liquid Fe-S alloys, which may serve as the fundamental parameters to model the Earth’s outer core.

September 20, 2020

Some geometrical properties of fission-track-surface intersections in apatite

Raymond Jonckheere, Carolin Aslanian, Bastian Wauschkuhn, Lothar Ratschbacher

Page range: 1355-1364

Abstract

Parallel fission-track-surface intersections identify the grains in an etched apatite mount that have been polished parallel to their prism faces and mark the orientations of their c -axes. Their lengths ( D par ) are a practical kinetic parameter that is indicative of the track annealing rate of apatite. Little is known, however, about their geometrical properties in non-prism faces. We present a model calculation of the frequency distributions of the orientations, lengths, and widths of track-surface intersections in non-prism faces. The current model does not include the efects of surface etching or measurement imprecision. However, as far as it goes, it is consistent with measurements in apatite surfaces up to 30° to the c -axis. Regardless of the model, we submit that the statistical properties of the fission-track-surface intersections have practical uses. The distribution of their orientations is characteristic of the orientation of the etched surface relative to the c -axis. The distribution of their lengths presents a possible tool for investigating track etching, in particular for evaluating the tracks added and lost through surface etching. The distribution of their widths is a potential kinetic parameter independent of surface orientation and less susceptible to the factors, such as the sampling method and surface etch rate, that produce conflicting D par values.

Open Access September 20, 2020

Thermal equation of state of post-aragonite CaCO₃-Pmmn

Mingda Lv, Jiachao Liu, Eran Greenberg, Vitali B. Prakapenka, Susannah M. Dorfman

Page range: 1365-1374

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Abstract

Calcium carbonate (CaCO 3 ) is one of the most abundant carbonates on Earth’s surface and transports carbon to Earth’s interior via subduction. Although some petrological observations support the preservation of CaCO 3 in cold slabs to lower mantle depths, the geophysical properties and stability of CaCO 3 at these depths are not known, due in part to complicated polymorphic phase transitions and lack of constraints on thermodynamic properties. Here we measured thermal equation of state of CaCO 3 - Pmmn , the stable polymorph of CaCO 3 through much of the lower mantle, using synchrotron X‑ray diffraction in a laser-heated diamond-anvil cell up to 75 GPa and 2200 K. The room-temperature compression data for CaCO 3 - Pmmn are fit with third-order Birch-Murnaghan equation of state, yielding K T0 = 146.7 (±1.9) GPa and K 0 = 3.4(±0.1) with V 0 fixed to the value determined by ab initio calculation, 97.76 Å 3 . High-temperature compression data are consistent with zero-pressure thermal expansion α T = a 0 + a 1 T with a 0 = 4.3(±0.3)×10 -5 K -1 , a 1 = 0.8(±0.2)×10 -8 K -2 , temperature derivative of the bulk modulus (∂ K T /∂ T ) P = –0.021(±0.001) GPa/K; the Grüneisen parameter γ 0 = 1.94(±0.02), and the volume independent constant q = 1.9(±0.3) at a fixed Debye temperature θ 0 = 631 K predicted via ab initio calculation. Using these newly determined thermodynamic parameters, the density and bulk sound velocity of CaCO 3 - Pmmn and (Ca,Mg)-carbonate-bearing eclogite are quantitatively modeled from 30 to 80 GPa along a cold slab geotherm. With the assumption that carbonates are homogeneously mixed into the slab, the results indicate the presence of carbonates in the subducted slab is unlikely to be detected by seismic observations, and the buoyancy provided by carbonates has a negligible effect on slab dynamics.

September 20, 2020

Structure of NaFeSiO₄, NaFeSi₂O₆, and NaFeSi₃O₈ glasses and glass-ceramics

Mostafa Ahmadzadeh, Alex Scrimshire, Lucy Mottram, Martin C. Stennett, Neil C. Hyatt, Paul A. Bingham, John S. McCloy

Page range: 1375-1384

Abstract

The crystallization of iron-containing sodium silicate phases holds particular importance, both in the management of high-level nuclear wastes and in geosciences. Here, we study three as-quenched glasses and their heat-treated chemical analogs, NaFeSiO 4 , NaFeSi 2 O 6 , and NaFeSi 3 O 8 (with nominal stoichiometries from feldspathoid, pyroxene, and feldspar mineral groups, i.e., Si/Fe = 1, 2, and 3, respectively) using various techniques. Phase analyses revealed that as-quenched NaFeSiO 4 could not accommodate all Fe in the glass phase (some Fe crystallizes as Fe 3 O 4 ), whereas as-quenched NaFeSi 2 O 6 and NaFeSi 3 O 8 form amorphous glasses. NaFeSi 2 O 6 glass is the only composition that crystallizes into its respective isochemical crystalline polymorph, i.e., aegirine, upon isothermal heat-treatment. As revealed by Mössbauer spectroscopy, iron is predominantly present as fourfold-coordinated Fe 3+ in all glasses, though it is present as sixfold-coordinated Fe 3+ in the aegirine crystals (NaFeSi 2 O 6 ), as expected from crystallography. Thus, Na-Fe silicate can form a crystalline phase in which it is octahedrally coordinated, even though it is mostly tetrahedrally coordinated in the parent glasses. Thermal behavior, magnetic properties, iron redox state (including Fe K -edge X‑ray absorption), and vibrational properties (Raman spectra) of the above compositions are discussed.

September 20, 2020

Raman spectroscopic studies of O–H stretching vibration in Mn-rich apatites: A structural approach

Adam Pieczka, Bożena Gołębiowska, Piotr Jeleń, Maciej Sitarz, Adam Szuszkiewicz

Page range: 1385-1391

Abstract

The O–H stretching vibration mode in crystals of (Mn,Cl)-rich and F-poor minerals of the apatite-supergroup has been studied by micro-Raman spectroscopy. The main purpose was to check if such an analysis can provide a quick and simple method to assess the distribution of Ca and Mn together with traces of Fe + Mg ( = Mn*) on nonequivalent cationic sites in the apatite structure, especially in small and strongly heterogeneous crystals directly in thin sections. The O–H stretching vibration mode can then be treated as a useful structural probe giving information on the M2 occupants bonded to X OH. Pieczkaite, with the empirical formula (Mn 4.49 Fe 0.47 Ca 0.05 Mg 0.01 ) Σ5.01 P 2.99 O 12 [Cl 0.83 (OH) 0.17 ], displays the O–H stretching mode centered at ~3380 cm –1 , which shows that the complete replacement of Ca by Mn* at the M2 site is connected with a shift of the O–H stretching band ~192 cm –1 toward lower wavenumbers in relation to the O–H Raman band position reported for hydroxylapatite. The value is high enough to be an indicator of the M2 Mn*···OH content in any sample of Mn-enriched apatite. Studies of the fine structure of the band disclosed its dependence on (1) the local combinations of Ca and Mn* forming triplets of M2 cations bonded to the X anion, (2) the presence of OH+Cl at the two half-occupied X sites that form chemical bonds with the M2 cations varying in strength and length, and (3) the spatial geometry of the X–M2 bonds and polarizability of the monovalent X anion by varying cations in the M2M2M2 triplets. The deconvolution of the band into maximum eight component bands with constant Raman shifts opens the possibility of evaluating the averaged M2M2M2 triplet bonded to oxygen of the X OH group. If the OH/ (OH+Cl) fraction is known, the amounts of Ca and Mn* bonded to X OH can also be estimated. Application of the method to the holotype parafiniukite showed a slightly diferent distribution of Ca in M2M2M2 triplets than had been assumed from single-crystal X‑ray diffraction. However, it corroborates suggestions that in the apatite structure there may be a preference for M2 Ca to be bonded to X OH and M2 Mn* to X Cl. Our results show that the proposed method can be used as an independent tool in structural studies of Mn-rich minerals of the apatite-supergroup, providing results complementary to single-crystal X‑ray diffraction. This method can easily be adjusted to modern apatite-type nanomaterials synthesized for biomedical and various industrial applications.

September 20, 2020

Characterization of modified mineral waste material adsorbent as affected by thermal treatment for optimizing its adsorption of lead and methyl orange

Lingcheng Su, Jiajun Chen, Huada Ruan, Dongqi Chen, Xi Chen, Chiuhong Lee

Page range: 1392-1403

Abstract

Thermal treatment is one of the most common processes in mineral modification, and this process has been applied to the modification of mineral waste material to improve its adsorption ability of methyl orange (MO) and lead (Pb) in this study. The properties of modified mineral waste material (MMWM) before and after thermal modification were characterized by using the Brunauer–Emmett–Teller (BET) N 2 adsorption/desorption measurement, field emission scanning electron microscope (FESEM) coupled with energy-dispersive X‑ray (EDX), X‑ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Phase transformation was investigated related to the change in surface morphology and dehydroxylation that occurred in MMWM samples during the process of thermal treatment. To study adsorption performances of Pb and MO onto the newly modified MMWM, several experiments were carried out under different adsorption conditions and the results were determined using inductively coupled plasma optical emission spectrometry (ICP-OES) and UV-Vis spectrophotometry. The thermally treated MMWM samples showed morphological transformation and an increasing trend in BET specific surface area (SSA) up to 500 °C followed by a decreasing trend till 1000 °C. Thermal modification of MMWM successfully improved Pb adsorption from 349 to 515 mg/g, corresponding to the MMWM modified at 600 °C, and the methyl orange (MO) adsorption from 68 to 87.6 mg/g at 400 °C. The adsorptions of Pb and MO were mainly chemisorption and monolayer coverage, as the pseudo-second-order model and the Langmuir equation displayed good correlations for Pb and MO adsorption data.

September 20, 2020

Morin-type transition in 5C pyrrhotite

Charles R.S. Haines, Giulio I. Lampronti, Wim T. Klooster, Simon J. Coles, Sian E. Dutton, Michael A. Carpenter

Page range: 1404-1411

Abstract

We report the discovery of a low-temperature spin-flop transition in 5 C pyrrhotite at ~155 K that is similar to those seen in hematite at 260 K and FeS (troilite) at 440 K. The 5 C crystal was produced by annealing a 4 C pyrrhotite crystal at 875 K to produce a change in the vacancy-ordering scheme that developed during cooling. The 5 C structure is confirmed by single-crystal X‑ray diffraction and the stoichiometry and homogeneity by electron microprobe and SEM BSE mapping. Resonant ultrasound spectroscopy (RUS), heat capacity, and magnetization measurements from room temperature down to 2 K are reported. The transition is marked by a steep change in elastic properties at the transition temperature, a peak in the heat capacity, and weak anomalies in measurements of magnetization. Magnetic hysteresis loops and comparison with the magnetic properties of 4 C pyrrhotite suggest that the transition involves a change in orientation of moments between two different antiferromagnetic structures, perpendicular to the crystallographic c- axis at high temperatures and parallel to the crystallographic c- axis at low temperatures. The proposed structures are consistent with a group theoretical treatment that also predicts a first-order transition between the magnetic structures.

September 20, 2020

The formation of marine red beds and iron cycling on the Mesoproterozoic North China Platform

Dongjie Tang, Jianbai Ma, Xiaoying Shi, Maxwell Lechte, Xiqiang Zhou

Page range: 1412-1423

Abstract

Marine red beds (MRBs) are common in sedimentary records, but their genesis and environmental implications remain controversial. Genetic models proposed for MRBs variably invoke diagenetic or primary enrichments of iron, with vastly different implications for the redox state of the contemporaneous water column. The Xiamaling Formation (ca. 1.4 Ga) in the North China Platform hosts MRBs that offer insights into the iron cycling and redox conditions during the Mesoproterozoic Era. In the Xiamaling MRBs, well-preserved, nanometer-sized flaky hematite particles are randomly dispersed in the clay (illite) matrix, within the pressure shadow of rigid detrital grains. The presence of hematite flake aggregates with multiple face-to-edge (“cardhouse”) contacts indicates that the hematite particles were deposited as loosely bound, primary iron oxyhydroxide flocs. No greenalite or other ferrous iron precursor minerals have been identified in the MRBs. Early diagenetic ankerite concretions hosted in the MRBs show non-zero I/(Ca+Mg) values and positive Ce anomalies (>1.3), suggesting active redox cycling of iodine and manganese and therefore the presence of molecular oxygen in the porewater and likely in the water column during their formation. These observations support the hypothesis that iron oxyhydroxide precipitation occurred in moderately oxygenated marine waters above storm wave base (likely <100 m). Continentally sourced iron reactivated through microbial dissimilatory iron reduction, and distal hydrothermal fluids may have supplied Fe(II) for the iron oxyhydroxide precipitation. The accumulation of the Xiamaling MRBs may imply a slight increase of seawater oxygenation and the existence of long-lasting adjacent ferruginous water mass.

September 20, 2020

A multi-methodological study of kernite, a mineral commodity of boron

G. Diego Gatta, Alessandro Guastoni, Paolo Lotti, Giorgio Guastella, Oscar Fabelo, Maria Teresa Fernandez-Diaz

Page range: 1424-1431

Abstract

Kernite, ideally Na 2 B 4 O 6 (OH) 2 ∙3H 2 O, is a major constituent of borate deposits and one of the most important mineral commodities of B. The chemical composition and crystal structure of kernite from the Kramer Deposit (Kern County, California) were investigated by a suite of analytical techniques (i.e., titrimetric determination of B content, gravimetric method for Na, ion selective electrode for F, high- T mass loss for H 2 O content, inductively coupled plasma atomic emission spectroscopy for REE and other minor elements, elemental analysis for C, N, and H contents) and single-crystal X‑ray (at 293 K) and neutron (at 20 K) diffraction. The concentrations of more than 50 elements were measured. The general experimental formula of the kernite sample used in this study is Na 1.99 B 3.99 O 6 (OH) 2 ∙3.01H 2 O. The fraction of other elements is, overall, insignificant: excluding B, kernite from the Kramer Deposit does not act as geochemical trap of other technologically relevant elements (e.g., Li, Be, or REE). The X‑ray and neutron structure model obtained in this study confirms that the structure of kernite is built up by: two (crystallographically independent) triangular BO 2 OH groups and two tetrahedral BO 4 groups, which share corner-bridging O atoms to form threefold rings, giving chains running along [010], and NaO 4 (OH)(OH 2 ) and NaO 2 (OH)(OH 2 ) 3 polyhedra. Positional disorder of two H sites of H 2 O molecules was observed by the neutron structure refinement and corroborated by the maximum-entropy method calculation, which consistently provided a model based on a static disorder, rather than a dynamic one. The H-bonding network in the structure of kernite is complex, pervasive, and plays a primary role on its structural stability: the majority of the oxygen sites are involved in H-bonding, as donors or as acceptors . The potential utilizations of kernite, as a source of B (B 2 O 3 ~50 wt%), are discussed, on the basis of the experimental findings of this study.

Letter

September 20, 2020

Si-rich Mg-sursassite Mg₄Al₅Si₇O₂₃(OH)₅ with octahedrally coordinated Si: A new ultrahigh-pressure hydrous phase

Luca Bindi, Mark D. Welch, Aleksandra A. Bendeliani, Andrey V. Bobrov

Page range: 1432-1435

Abstract

The crystal structure of a new high-pressure hydrous phase, Si-rich Mg-sursassite, of ideal composition Mg 4 Al 5 Si 7 O 23 (OH) 5 , that was produced by sub-solidus reaction at 24 GPa and 1400 °C in an experiment using a model sedimentary bulk composition, has been determined by single-crystal X‑ray diffraction. The phase was found to be topologically identical to Mg-sursassite, Mg 5 Al 5 Si 6 O 21 (OH) 7 , and has space group P 2 1 / m and lattice parameters a = 8.4222(7), b = 5.5812(3), c = 9.4055(9) Å, β = 106.793(8)°, V = 423.26(6) Å 3 , and Z = 1. The empirical formula determined by electron microprobe analysis of the same crystal as was used in the X‑ray experiment is [Mg 3.93(3) Fe 0.03(1) ] S3.96 [Al 4.98(3) Cr 0.04(1) ] S5.02 Si 7.02(4) O 23 (OH) 5 , with hydroxyl content implied by the crystal-structure analysis. The most significant aspect of the structure of Si-rich Mg-sursassite is the presence of octahedrally coordinated Si. Its structural formula is M1,VIIMg2 M2VIMg22+ M3,VI(Al0.5Si0.5)2 M4,VIAl2 M5,VIAl2T1,IVSi2 T2,IVSi2 T3,IVSi2 O23(OH)5.$^{M1,\text{VII}}M{{g}_{2}}{{\,}^{{{M}_{2}}\text{VI}}}\text{Mg}{{_{2}^{2+}}^{\,M3\text{,VI}}}{{\left( \text{A}{{\text{l}}_{\text{0}\text{.5}}}\text{S}{{\text{i}}_{\text{0}\text{.5}}} \right)}_{2}}{{\,}^{M4\text{,VI}}}\text{A}{{\text{l}}_{2}}{{\,}^{{{M}_{5}}\text{,VI}}}\text{A}{{\text{l}}_{2}}^{T1\text{,IV}}\text{S}{{\text{i}}_{\text{2}}}{{\,}^{T2\text{,IV}}}\text{S}{{\text{i}}_{2}}{{\,}^{T3\text{,IV}}}\text{S}{{\text{i}}_{2}}\,\,{{\text{O}}_{\text{23}}}{{\left( \text{OH} \right)}_{\text{5}}}.$Si-rich Mg-sursassite joins the group of hydrous ultrahigh-pressure phases with octahedrally coordinated Si that have been discovered by experiment, and that may play a significant role in the distribution and hosting of water in the deep mantle at subduction zones. The reactions defining the stability of Si-rich Mg-sursassite are unknown, but are likely to be fundamentally diferent from those of Mg-sursassite, and involve other ultrahigh-pressure dense structures such as phase D, rather than phase A.

September 20, 2020

Inherited Eocene magmatic tourmaline captured by the Miocene Himalayan leucogranites

Jinsheng Han, Pete Hollings, Fred Jourdan, Yunchuan Zeng, Huayong Chen

Page range: 1436-1440

Abstract

The Miocene Cuonadong leucogranites in the easternmost section of the Tethyan Himalaya, Southern Tibet, are characterized by two types of tourmaline. Tourmaline occurs as needle-like crystals in the two-mica ± tourmaline granites (Tur G) and large patches in the pegmatites (Tur P). Both the granite and the pegmatites yield Miocene ages (ca. 20 Ma) based on monazite U(-Th)-Pb dating, whereas 40 Ar/ 39 Ar geochronology of the coarse-grained tourmalines (Tur P) crosscut by pegmatite veins yielded an Eocene mini-plateau age of 43 ± 6 Ma. Major element concentrations of tourmaline indicate that both Tur P and Tur G belong to the schorl group with a magmatic origin, but trace elements such as V indicate that they are not cogenetic. Boron isotopes suggest that Tur P (average –9.76‰) was derived from typical crustal sources, whereas Tur G (average –7.65‰) contains relatively more mafic input. The capture of Eocene tourmaline by the Miocene leucogranites at Cuonadong suggests that the crustally derived Eocene magmatism may have occurred in the southern Tethyan Himalaya. Identification of the inherited magmatic tourmaline (Tur P), although not common, challenges the current application of tourmaline chemistry to the investigation of magmatic-hydrothermal systems.

Open Access September 20, 2020

Memorial of F. Donald Bloss 1920–2020

Mickey E. Gunter

Page range: 1441-1442

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Open Access September 20, 2020

Book Review

Keith Daniel Putirka

Page range: 1443-1444

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About this journal

Objective
American Mineralogist: Journal of Earth and Planetary Materials (Am Min), is the flagship journal of the Mineralogical Society of America (MSA), continuously published since 1916. Am Min is home to some of the most important advances in the Earth Sciences. Our mission is a continuance of this heritage: to provide readers with reports on original scientific research, both fundamental and applied, with far reaching implications and far ranging appeal. Topics of interest cover all aspects of planetary evolution, and biological and atmospheric processes mediated by solid-state phenomena. These include, but are not limited to, mineralogy and crystallography, high- and low-temperature geochemistry, petrology, geofluids, bio-geochemistry, bio-mineralogy, synthetic materials of relevance to the Earth and planetary sciences, and breakthroughs in analytical methods of any of the aforementioned.

For the complete Scope & Mission of Am Min click here

Topics

Planetary evolution
Biological and atmospheric processes mediated by solid-state phenomena
Mineralogy
Crystal chemistry
High- and low-temperature geochemistry
Biomineralization
Geofluids
Bio-geochemistry
Bio-mineralogy
Synthetic materials
Mineral Physics
Crystallography
Crystal structure
Martian rock and soil
Raman spectroscopy
Petrology
Planetary materials
Infrared spectroscopy

Article formats
Original, fundamental and applied research articles

Information on Submission Process

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Volume 105 Issue 9

Issue of American Mineralogist

How American Mineralogist and the Mineralogical Society of America influenced a career in mineralogy, petrology, and plate pushing, and thoughts on mineralogy’s future role

Abstract

Petrographic and spectral study of hydrothermal mineralization in drill core from Hawaii: A potential analog to alteration in the martian subsurface

Abstract

Characterizing low-temperature aqueous alteration of Mars-analog basalts from Mauna Kea at multiple scales

Abstract

Archean to Paleoproterozoic seawater halogen ratios recorded by fluid inclusions in chert and hydrothermal quartz

Abstract

Metasomatism-controlled hydrogen distribution in the Spitsbergen upper mantle

Abstract

Phase transformation of hydrous ringwoodite to the lower-mantle phases and the formation of dense hydrous silica

Abstract

Density and sound velocity of liquid Fe-S alloys at Earth’s outer core P-T conditions

Abstract

Some geometrical properties of fission-track-surface intersections in apatite

Abstract

Thermal equation of state of post-aragonite CaCO3-Pmmn

Abstract

Structure of NaFeSiO4, NaFeSi2O6, and NaFeSi3O8 glasses and glass-ceramics

Abstract

Raman spectroscopic studies of O–H stretching vibration in Mn-rich apatites: A structural approach

Abstract

Characterization of modified mineral waste material adsorbent as affected by thermal treatment for optimizing its adsorption of lead and methyl orange

Abstract

Morin-type transition in 5C pyrrhotite

Abstract

The formation of marine red beds and iron cycling on the Mesoproterozoic North China Platform

Abstract

A multi-methodological study of kernite, a mineral commodity of boron

Abstract

Si-rich Mg-sursassite Mg4Al5Si7O23(OH)5 with octahedrally coordinated Si: A new ultrahigh-pressure hydrous phase

Abstract

Inherited Eocene magmatic tourmaline captured by the Miocene Himalayan leucogranites

Abstract

Memorial of F. Donald Bloss 1920–2020

Book Review

Thermal equation of state of post-aragonite CaCO₃-Pmmn

Structure of NaFeSiO₄, NaFeSi₂O₆, and NaFeSi₃O₈ glasses and glass-ceramics

Si-rich Mg-sursassite Mg₄Al₅Si₇O₂₃(OH)₅ with octahedrally coordinated Si: A new ultrahigh-pressure hydrous phase