Editor’s Notes
Total Results: 1697
Volume 104 : July 2019 Issue
The quench control of water estimates in convergent margin magmas
https://doi.org/10.2138/am-2019-6735
Gavrilenko et al.’s article on page 936, “The quench control of water estimates in convergent margin magmas,” explores the limits of melt inclusions (MIs) as hydrous magma recorders in an experimental study, showing that there is a limit of dissolved H2O that mafic glassy MIs can retain. These results show there is potential bias in the glassy MI data set; they can only faithfully record pre-eruptive H2O contents in the upper-most part of the Earth’s crust where H2O-solubility is low. The current MI database cannot be used to robustly estimate the full range of arc magmas and therefore assess volatile budgets in primitive or evolved compositions. Such magmas may contain much larger amounts of H2O than currently recognized, and the diversity of magma evolutionary pathways in subduction zones is likely being significantly underappreciated.
Textural and chemical variations of micas as indicators for tungsten mineralization: Evidence from highly evolved granites in the Dahutang tungsten deposit, South China
https://doi.org/10.2138/am-2019-6796
Yin et al. (page 949) studied the “Textural and chemical variations of micas as indicators for tungsten mineralization: Evidence from highly evolved granites in the Dahutang tungsten deposit, South China.” They found that micas are effective indicators not only for the magmatic-hydrothermal evolution of granite but also for the tungsten mineralization. The texture of zoned micas and geochemical variations of micas are important for reconstructing tungsten ore-forming processes, including the enrichment and transportation of tungsten during the magmatic-hydrothermal evolution. Tungsten is unlikely to be deposited directly in the granite, and reducing fluids and fluid-rock interaction play an import role in forming large ore deposits.
A topological model for defects and interfaces in complex crystal structures
https://doi.org/10.2138/am-2019-6892
Hirth et al. (page 966) in “A topological model for defects and interfaces in complex crystal structures” introduce a tractable method for applying the topological model to characterize defects in these complex materials. They illustrate how structural groups, each with a motif containing multiple atoms, provide lattices and structures that are useful in describing dislocations and disconnections in interfaces. They illustrate the model for twinning in albite owing to its potential application for constraining the rheological properties of the crust at conditions near the brittle-plastic transition, where plagioclase is a major constituent of common rock types. The concept of structural groups makes an analysis of the twinning process easier in complex minerals and explicitly predicts the interface structure of the deformation twins.
Phoxite, (NH4)2Mg2(C2O4)(PO3OH)2(H2O)4, the first phosphate-oxalate mineral
https://doi.org/10.2138/am-2019-6991
Kampf et al. (page 973) describe the new mineral “Phoxite, (NH4)2Mg2(C2O4)(PO3OH)2(H2O)4, the first phosphate-oxalate mineral.” Phoxite is a new mineral species found in an unusual bat-guano-related, post-mining assemblage of phases in the Rowley mine, Maricopa County, Arizona, U.S.A. It is the first mineral known to contain both phosphate and oxalate groups and it possesses a novel layer structure that can be considered a “soft framework” due to strong hydrogen bonding between layers. The phase may have potential uses in agricultural applications for soil conditioning, fertilizing, and as a natural pesticide.
Crystallographic and textural evidence for precipitation of rutile, ilmenite, corundum, and apatite lamellae from garnet
https://doi.org/10.2138/am-2019-6849
Keller and Ague (page 980) investigated “Corundum, and apatite lamellae from garnet.” Multiple lines of evidence support the precipitation of rutile, ilmenite, apatite, and corundum lamellae from garnet. Crystallographic orientation relationships (COR) between inclusion and host are consistent from independent occurrences worldwide, and minerals of the same crystal system share preferred relationships. Rutile forms a COR angularly equivalent to the Widmanstätten pattern in meteorites. These COR are valuable for comparing precipitation behavior across materials and suggest lamellae are precipitates indicative of precursor garnet chemistry.
A low-aluminum clinopyroxene-liquid geothermometer for high-silica magmatic systems
https://doi.org/10.2138/am-2019-6842
Brugman and Till’s (page 996) “A low-aluminum clinopyroxene-liquid geothermometer for high-silica magmatic systems” presents a new clinopyroxene-liquid geothermometer calibrated for use with high-Fe, low-Al clinopyroxene from high-silica systems. It lowers calculated temperatures by 85 °C on average relative to a popular geothermometer (Putirka 2008, Eq. 33) and reduces the uncertainty by a factor of two (standard error of estimate ± 20 °C). When applied to natural systems, this clinopyroxene-liquid geothermometer reconciles many inconsistencies between experimental phase equilibria and preexisting geothermometry results for silicic volcanism, including those from the Bishop Tuff and Yellowstone caldera-forming and post-caldera rhyolites. Clinopyroxene is found not restricted to near-liquidus temperatures in rhyolitic systems and can be stable over a broad temperature range, often down to the solidus.
Compressibility of synthetic Mg-Al tourmalines to 60 GPa
https://doi.org/10.2138/am-2019-6967
Berryman et al. (page 1005) in “Compressibility of synthetic Mg-Al tourmalines to 60 GPa” established the pressure-volume equation of state of tourmaline and its room-temperature metastability to 60 GPa in a series of high-pressure single-crystal X-ray diffraction experiments. The use of synthetic tourmalines representing five distinct end-member species revealed the primary role of the octahedral sites, particularly the Z site, on tourmaline’s compressibility and its remarkable metastability. This study highlights the utility of synthetic crystals in exploring compositional and structural controls on mineral properties at high pressure.
The single-crystal elastic properties of the jadeite-diopside solid solution and their implications for the composition-dependent seismic properties of eclogite
https://doi.org/10.2138/am-2019-6990
Hao et al. (page 1016) measured “The single-crystal elastic properties of the jadeite-diopside solid solution and their implications for the composition-dependent seismic properties of eclogite.” The 13 single-crystal adiabatic elastic moduli (Cij) of a C2/c jadeite sample close to the ideal composition (NaAlSi2O6) and a natural P2/n diopside-rich omphacite sample were measured at ambient conditions by Brillouin spectroscopy. Voigt-Reuss-Hill averaging of the Cij values yields an aggregate bulk modulus, KS, = 138(3) GPa and shear modulus, G, = 84(2) GPa for jadeite. The vpvs of omphacite decrease with diopside content, though the velocity changes are small as diopside component exceeds 70%. They also found that both the isotropic vpvs, as well as the seismic anisotropy of eclogite, changed strongly with the bulk-chemical composition. The relationship between the anisotropic velocities of eclogite and the chemical composition can be a useful tool to trace the origin of the eclogitic materials in the Earth’s mantle.
Elasticity of single-crystal low water content hydrous pyrope at high-pressure and high-temperature conditions
https://doi.org/10.2138/am-2019-6897
Fan et al.’s (page 1022) “Elasticity of single-crystal low water content hydrous pyrope at high-pressure and high-temperature conditions” reports measurements of the acoustic wave velocities and density of a single-crystal, hydrous pyrope with ~900 ppmw H2O by Brillouin light scattering combined with in situ synchrotron X-ray diffraction in the diamond anvil cell up to 18.6 GPa at room temperature and up to 700 K at ambient pressure. The modeling results indicate that hydrous pyrope remains almost elastically isotropic at relevant high P-T conditions and may have no significant contribution to seismic anisotropy in the upper mantle. Furthermore, hydrogen has no significant effect on the seismic velocities and the Vp/Vs ratio of pyrope at the upper mantle P-T conditions, especially for the limited hydration level (<100 ppmw H2O) of mantle-derived garnets.
Determination of the oxidation state of iron in Mid-Ocean Ridge basalt glasses by Raman spectroscopy
https://doi.org/10.2138/am-2019-6887
Le Losq et al.’s study (page 1032) “Determination of the oxidation state of iron in Mid-Ocean Ridge basalt glasses by Raman spectroscopy” used conventional, as well as machine learning, data reduction methods to measure the iron oxidation state of Mid-Ocean Ridge Basalt (MORB) glasses, a key parameter for understanding upper mantle conditions and oceanic seafloor production, from their Raman spectra. The approaches allow evaluation of the average iron oxidation state in MORB glasses as 0.09 and to predict MORB glass chemical composition. Because Raman spectroscopy is fast, non-destructive, has microscale resolution and has the potential to be portable (e.g., the SHERLOC system that equips the Mars 2020 rover), its combination with machine learning approaches have a strong potential for analysis of materials in environments inaccessible by other conventional techniques, like Mid-Ocean ridges.
Lepageite, Mn32+(Fe73+Fe42+)O3[Sb53+As83+O34], a new arsenite-antimonite mineral from the Szklary pegmatite, Lower Silesia, Poland
https://doi.org/10.2138/am-2019-6903
Pieczka et al.’s paper (page 1043) “Lepageite, Mn2+3(Fe3+7Fe2+4)O3[Sb3+5As3+8O34]], a new arsenite-antimonite mineral from the Szklary pegmatite, Lower Silesia, Poland” presents data on a new mineral, lepageite, that is a representative of a rare mineral group of arsenite-antimonites, discovered in the Szklary LCT pegmatite in Poland. We describe its chemical composition and crystal structure and finally explain by genetic implications why arsenite-antimonite minerals are rare species in a pegmatitic environment.
High-temperature structural change and microtexture formation of sillimanite and its phase relation with mullite
https://doi.org/10.2138/am-2019-6732
Igami et al. (page 1051) investigated the “High-temperature structural change and microtexture formation of sillimanite and its phase relation with mullite.” Synchrotron X-ray diffraction experiments and transmission electron microscopy of heated sillimanite at various pressures were conducted to clarify the detailed phase relations between sillimanite and mullite. As a result, they propose a new P-T diagram for the Al2SiO5 system with the mullitization boundary and the Al/Si order parameter of sillimanite. Investigations of sillimanite/mullite based on the present results can yield new information about thermal histories in high-temperature regions that is easy to be lost in general.
Memorial of Paul Brian Moore 1940–2019
https://doi.org/10.2138/am-2019-m690
Hawthorne et al. (page 1062) in their “Memorial of Paul Brian Moore 1940–2019” remember one of the most prolific mineralogists of the 20th century and highlight his contributions to our science.
Volume 104 : June 2019 Issue
Why scientists should study chess
https://doi.org/10.2138/am-2019-Ed104611
This issue of American Mineralogist starts with an interesting and thoughtful Editorial by the former Editor Keith Putirka (page 785): Why scientists should study chess.
Neither antigorite nor its dehydration is “metastable”
https://doi.org/10.2138/am-2019-6957
In a “highlights and breakthroughs” article, Ferrand (page 788) comments on the paper “Kinetics of antigorite dehydration: Rapid dehydration as a trigger for lower-plane seismicity in subduction zones” by Liu et al. (2019, Vol. 104, no. 2, pages 282-290). The study by Liu et al. confirms that antigorite dehydration is fast enough to trigger brittle failure under subduction conditions. The dehydration was found to involve two dehydroxylation mechanisms, allowing better understanding of the two-step antigorite destabilization observed in high-pressure experiments.
Geothermometry of the western half of the Central Metasedimentary Belt, Grenville Province, Ontario, and its implications
https://doi.org/10.2138/am-2019-6757
Dunn et al. (page 791) performed calcite-graphite carbon isotope thermometry on 150 marble samples from the western Central Metasedimentary Belt (CMB) of the Ontario segment of the Grenville Province, which represents the deeply eroded and exposed core of a major mountain chain that existed one billion years ago. The obtained data show a gradual increase in the peak metamorphic temperature from <500 °C in the Tudor Township area in the east to >700 °C along the western margin of the CMB. These results refine our understanding of orogenic buildup and collapse in the Grenville, including the styles of deformation of crystalline rocks in continental crust. The authors also found unusually high carbon isotope ratios (13C/12C) in the sample which provides a useful chemical marker to correlate rocks that formed in similar marine settings at around the same time roughly 1.3 billion years ago, well before the large mountain-building event.
An evolutionary system of mineralogy: Proposal for a classification of planetary materials based on natural kind clustering
https://doi.org/10.2138/am-2019-6709CCBYNCND
"In his Roebling Medal Paper, Hazen (page 810) describes a classification of planetary materials based on natural kind clustering. Minerals reveal the nature of the co-evolving geosphere and biosphere through billions of years of Earth history. Mineral classification systems have the potential to elucidate this rich evolutionary story; however, the present mineral taxonomy, based as it is on idealized major element chemistry and crystal structure, lacks a temporal aspect and thus cannot reflect planetary evolution. A complementary evolutionary system of mineralogy based on the quantitative recognition of ""natural kind clustering"" for a wide range of condensed planetary materials with different paragenetic origins (best revealed through the data-driven methods of cluster analysis) has the potential to amplify, though not supersede, the present classification system."
The composition and mineralogy of rocky exoplanets: A survey of >4000 stars from the Hypatia Catalog
https://doi.org/10.2138/am-2019-6787
Putirka and Rarick (page 817) survey the compositions and mineralogy of >4000 nearby stars from the Hypatia Catalog (the most compositionally broad of such collections) to determine whether such exoplanets might be geologically similar to Earth. They find that most exoplanets will have rocky compositions that are similar to Earth and so most exoplanets might exhibit plate tectonics, and so might also be Earth-like in other respects, for example, by harboring life.
New insights into the zircon-reidite phase transition
https://doi.org/10.2138/am-2019-6827
Stangarone et al. (page 830) used density functional theory (DFT) simulations of the structures of zircon and reidite (polymorphs of ZrSiO4) to show that above 20 GPa zircon undergoes a displacive phase transition to a new polymorph (space group I-42d) which may trigger the reconstructive transformation to reidite. Thus, this study provides new insights into the zircon-reidite transition, which may be induced by shock in meteorite impacts. The results clarify the discrepancies between previous observations on natural and experimental samples.
The effects of contrasting Ti and Al activities on Mn/Fe systematics in pyroxene from lunar mare basalts
https://doi.org/10.2138/am-2019-6875
Papike et al. (page 838) investigated the effects of contrasting Ti and Al activities on Mn/Fe systematics in pyroxene from lunar mare basalts. In terms of using Mn/Fe ratios for determining planetary parentage and the reasons for dispersion in this trend for each body, variation in oxygen fugacity appears to be the most important factor for Martian basalts. For lunar mare basalts, however, high Ti activity in the melting zone and the melts, and crystallization sequence differences among high-Ti, low-Ti, and very low-Ti basalts account for almost all of the observed dispersion in the Mn/Fe ratios. This study gives important insight into the challenges of establishing planetary parentage by use of Mn/Fe ratios in lunar pyroxene, and explores the effects of crystallization sequence (order of appearance on liquidus) on this parameter.
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