European Journal of Mineralogy最新文献

{"title":"Dislocation and disclination densities in experimentally deformed polycrystalline olivine","authors":"S. Demouchy, M. Thieme, F. Barou, B. Beausir, V. Taupin, P. Cordier","doi":"10.5194/ejm-35-219-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-219-2023","url":null,"abstract":"Abstract. We report a comprehensive data set characterizing and\u0000quantifying the geometrically necessary dislocation (GND) density in the\u0000crystallographic frame (ραc) and disclination density\u0000(ρθ) in fine-grained polycrystalline olivine deformed in\u0000uniaxial compression or torsion, at 1000 and 1200 ∘C, under a confining pressure of 300 MPa. Finite strains range from 0.11 up\u0000to 8.6 %, and stresses reach up to 1073 MPa. The data set is a selection\u0000of 19 electron backscatter diffraction maps acquired with conventional\u0000angular resolution (0.5∘) but at high spatial resolution (step\u0000size ranging between 0.05 and 0.1 µm). Thanks to analytical\u0000improvement for data acquisition and treatment, notably with the use of ATEX (Analysis Tools for Electron and X-ray diffraction)\u0000software, we report the spatial distribution of both GND and disclination\u0000densities. Areas with the highest GND densities define sub-grain boundaries.\u0000The type of GND densities involved also indicates that most olivine sub-grain\u0000boundaries have a mixed character. Moreover, the strategy for visualization also\u0000permits identifying minor GND that is not well organized as sub-grain boundaries\u0000yet. A low-temperature and high-stress sample displays a higher but less organized GND density than in a sample deformed at high temperature for a similar\u0000finite strain, grain size, and identical strain rate, confirming the action\u0000of dislocation creep in these samples, even for micrometric grains (2 µm). Furthermore, disclination dipoles along grain boundaries are identified\u0000in every undeformed and deformed electron backscatter diffraction (EBSD) map, mostly at the junction of a\u0000grain boundary with a sub-grain but also along sub-grain boundaries and at\u0000sub-grain boundary tips. Nevertheless, for the range of experimental\u0000parameters investigated, there is no notable correlation of the disclination\u0000density with stress, strain, or temperature. However, a broad positive\u0000correlation between average disclination density and average GND density per\u0000grain is found, confirming their similar role as defects producing\u0000intragranular misorientation. Furthermore, a broad negative correlation\u0000between the disclination density and the grain size or perimeter is found,\u0000providing a first rule of thumb on the distribution of disclinations. Field\u0000dislocation and disclination mechanics (FDDM) of the elastic fields due to\u0000experimentally measured dislocations and disclinations (e.g., strains/rotations and stresses) provides further evidence of the interplay\u0000between both types of defects. At last, our results also support that\u0000disclinations act as a plastic deformation mechanism, by allowing rotation\u0000of a very small crystal volume.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43192760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cation and anion ordering in synthetic lepidolites and lithian muscovites: influence of the OH ∕ F and Li ∕ Al ratios on the mica formation studied by NMR (nuclear magnetic resonance) spectroscopy and X-ray diffraction","authors":"Lara Sulcek, B. Marler, M. Fechtelkord","doi":"10.5194/ejm-35-199-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-199-2023","url":null,"abstract":"Abstract. A large number of lepidolites\u0000K(LixAl3−x)[Si2xAl4−2xO10](OH)yF2−y\u0000and Li-muscovites K(LixAl2-x/3□1-2x/3)[Si3AlO10](OH)yF2−y were synthesised by a gelling method in combination with hydrothermal\u0000syntheses at a pressure of 2 kbar and a temperature of 873 K. The nominal\u0000composition ranged between 0.0≤x≤2.0 and 0.0≤y≤2.0, i.e. from polylithionite\u0000K[Li2.0Al][Si4.0O10](OH)yF2−y over\u0000trilithionite\u0000K[Li1.5Al1.5][AlSi3.0O10](OH)yF2−y to muscovite K[Al2.0□][AlSi3.0O10](OH)yF2−y. 1H, 19F,\u000029Si and 27Al magic-angle spinning nuclear magnetic resonance (MAS\u0000NMR) and 27Al multiple-quantum magic-angle spinning (MQMAS) NMR\u0000spectroscopy has been performed to investigate the order and/or disorder state of\u0000Si and Al in the tetrahedral layers and of Li, Al, OH and F in the\u0000octahedral layer. The synthetic mica crystals are very small, ranging from\u00000.1 to 5 µm. With increasing Al content, the crystal sizes\u0000decrease. Rietveld structure analyses on 12 samples showed that nearly all\u0000samples consist of two mica polytypes (1M and 2M1) of varying\u0000proportions. In the case of lepidolites, the 1M / 2M1 ratio depends on\u0000the Li/Al ratio of the reaction mixture. The refinement of the occupancy\u0000factors of octahedral sites shows that lepidolites (1.5≤x≤2.0)\u0000represent a solid solution series with polylithionite and trilithionite as\u0000the endmembers. In the case of the Li-muscovites (0.0≤x≤1.5),\u0000the 1M / 2M1 ratio depends on the number of impurity phases like\u0000eucryptite or sanidine depleting the reaction mixture of Li or Al. There is\u0000no solid solution between trilithionite and muscovite; instead, the\u0000Li-muscovite crystals consist of domains differing in the relative\u0000proportions of muscovite and trilithionite. The overall composition of the synthesised micas which consist of two\u0000polytypes can be characterised by 29Si, 1H and 19F MAS NMR\u0000spectroscopy. The Si/Al ratio in the tetrahedral layers and thus the content\u0000of [4]Al were calculated by analysing the signal intensities of the\u000029Si MAS NMR experiments. The Li content xest was calculated from\u0000the measured tetrahedral Si/Al ratio of the 29Si MAS NMR signals. The\u0000calculated Li contents xest of samples between polylithionite and\u0000trilithionite agree with the expected values. The F-rich samples show slightly\u0000increased values and the OH samples lower values. Lepidolites with only F\u0000(x = 1.5 to 2.0, y = 0.0), but not lepidolites with only OH (x = 1.5 to 2.0\u0000and y = 2.0), were observed after synthesis. With decreasing Li content, x≤1.2, Li-muscovites containing mostly hydroxyl (y>1.0) are\u0000formed. It was possible to synthesise fluorine containing micas with a\u0000Li content as low as 0.3 and y = 0.2 to 1.8. The 19F and 1H MAS NMR\u0000experiments reveal that F and OH are not distributed statistically but local\u0000structural preferences exist. F is attracted by Li-rich and OH by Al-rich\u0000environments. The quadrupolar coupling constant which represents the\u0000anisotropy of the Al coordination is low for polylithionite with CQ=1.5 MHz and increases to CQ","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47074832","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pleysteinite, [(H2O)0.5K0.5]2Mn2Al3(PO4)4F2(H2O)10  ⋅  4H2O, the Al analogue of benyacarite, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany","authors":"I. Grey, R. Hochleitner, Christian Rewitzer, A. R. Kampf, C. MacRae, R. Gable, W. G. Mumme, E. Keck, C. Davidson","doi":"10.5194/ejm-35-189-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-189-2023","url":null,"abstract":"Abstract. Pleysteinite,\u0000[(H2O)0.5K0.5]2Mn2Al3(PO4)4F2(H2O)10 ⚫ 4H2O, is the aluminium analogue of benyacarite, from the\u0000Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany. It was found in\u0000specimens of altered zwieselite, in association with nordgauite, fluellite,\u0000rockbridgeite, pyrite and columbite. Pleysteinite occurs as isolated and\u0000small aggregates of colourless, stubby prisms that are typically 10 to 30 µm wide and up to 100 µm long. The crystals are flattened on\u0000{010} and bounded by {111}, {100} and {001} planes. The calculated density is 2.34 g cm−3. Optically, pleysteinite crystals are biaxial (+), with α=1.566(2), β=1.580(2), γ=1.600(2) (measured in\u0000white light) and 2V(meas.) = 80(1)∘. The empirical formula from\u0000electron microprobe analyses and structure refinement is\u0000[(H2O)0.50K0.50]2(Mn1.20Mg0.49Fe0.272+Zn0.05)∑2.01(Al1.63Fe0.203+Ti0.194+)∑2.02(Al0.56Ti0.444+)\u0000(PO4)4.02[F0.58O0.31(OH)0.11]2(H2O)10 ⚫ 3.92H2O. Pleysteinite has orthorhombic symmetry, with space group\u0000Pbca and unit-cell parameters a = 10.4133(8) Å, b=20.5242(17) Å, c=12.2651(13) Å,\u0000V=2621.4(4) Å3 and Z=4. The crystal structure was refined\u0000using single-crystal data to wRobs=0.054 for 1692 reflections with\u0000I>3σ(I). The crystal structure contains corner-connected\u0000linear trimers of Al-centred octahedra that share corners with PO4\u0000tetrahedra to form 10-member rings parallel to (010). K+ cations and\u0000water molecules are located in the rings. Additional corner-sharing of the\u0000PO4 tetrahedra with Mn(H2O)4O2 octahedra occurs along\u0000[010] to complete the 3D framework structure.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48329195","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pervasive carbonation of peridotite to listvenite (Semail Ophiolite, Sultanate of Oman): clues from iron partitioning and chemical zoning","authors":"Thierry Decrausaz, M. Godard, M. Menzel, F. Parat, E. Oliot, Romain Lafay, F. Barou","doi":"10.5194/ejm-35-171-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-171-2023","url":null,"abstract":"Abstract. Earth's long-term cycling of carbon is regulated from\u0000mid-ocean ridges to convergent plate boundaries by mass transfers involving\u0000mantle rocks. Here we examine the conversion of peridotite to listvenite\u0000(magnesite + quartz rock) during CO2 metasomatism along the basal\u0000thrust of the Semail Ophiolite (Fanja, Sultanate of Oman). At the outcrop\u0000scale, this transformation defines reaction zones, from serpentinized\u0000peridotites to carbonated serpentinites and listvenites. Based on a\u0000detailed petrological and chemical study, we show that carbonation\u0000progressed through three main stages involving the development of replacive\u0000textures ascribed to early stages, whilst carbonate (± quartz) veining\u0000becomes predominant in the last stage. The pervasive replacement of\u0000serpentine by magnesite is characterized by the formation of spheroids,\u0000among which two types are identified based on the composition of their core\u0000regions: Fe-core and Mg-core spheroids. Fe zoning is a type feature of\u0000matrix and vein magnesite formed during the onset carbonation (Stage 1).\u0000While Fe-rich magnesite is predicted to form at low fluid XCO2 from a\u0000poorly to moderately oxidized protolith, our study evidences that the local\u0000non-redox destabilization of Fe oxides into Fe-rich magnesite is essential to\u0000the development of Fe-core spheroids. The formation of Fe-core spheroids is\u0000followed by the pervasive (over-)growth of Mg-rich spheroids and aggregates\u0000(Stage 2) at near-equilibrium conditions in response to increasing fluid\u0000XCO2. Furthermore, the compositions of carbonates indicate that most\u0000siderophile transition elements released by the dissolution of primary\u0000minerals are locally trapped in carbonate and oxides during matrix\u0000carbonation, while elements with a chalcophile affinity are the most likely\u0000to be leached out of reaction zones.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44053777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thermodynamic and structural variations along the olivenite–libethenite solid solution","authors":"J. Majzlan, Alexandra M. Plumhoff, M. Števko, G. Steciuk, J. Plášil, E. Dachs, A. Benisek","doi":"10.5194/ejm-35-157-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-157-2023","url":null,"abstract":"Abstract. Many natural secondary arsenates contain a small fraction of phosphate. In\u0000this work, we investigated the olivenite–libethenite\u0000(Cu2(AsO4)(OH)–Cu2(PO4)(OH)) solid solution as a model system\u0000for the P–As substitution in secondary minerals. The synthetic samples\u0000spanned the entire range from pure olivenite (Xlib=0) to\u0000libethenite (Xlib=1). Acid-solution calorimetry determined\u0000that the excess enthalpies are non-ideal, with a maximum at Xlib=0.6 of +1.6 kJ mol−1. This asymmetry can be described by the\u0000Redlich–Kister equation of Hex= Xoli⋅Xlib [A+B(Xoli−Xlib)], with A=6.27 ± 0.16 and B=2.9 ± 0.5 kJ mol−1.\u0000Three-dimensional electron diffraction analysis on the intermediate member\u0000with Xlib=0.5 showed that there is no P–As ordering, meaning\u0000that the configurational entropy (Sconf) can be calculated as\u0000-R(Xoliln⁡Xoli+Xlibln⁡Xlib). The excess vibrational entropies\u0000(Svibex), determined by relaxation calorimetry, are\u0000small and negative. The entropies of mixing (Sconf+Svibex) also show asymmetry, with a maximum near\u0000Xlib=0.6. Autocorrelation analysis of infrared spectra\u0000suggests local heterogeneity that arises from strain relaxation around\u0000cations with different sizes (As5+ / P5+) in the intermediate\u0000members and explains the positive enthalpies of mixing. The length scale of\u0000this strain is around 5 Å, limited to the vicinity of the tetrahedra in\u0000the structure. At longer length scales (≈15 Å), the strain is\u0000partially compensated by the monoclinic–orthorhombic transformation. The\u0000volume of mixing shows complex behavior, determined by P–As\u0000substitution and symmetry change. A small (0.9 kJ mol−1) drop in\u0000enthalpies of mixing in the region of Xlib=0.7–0.8 confirms\u0000the change from monoclinic to orthorhombic symmetry.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45145174","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mckelveyite group minerals – Part 2: Alicewilsonite-(YCe), Na2Sr2YCe(CO3)6  ⋅  3H2O, a new species","authors":"I. Lykova, R. Rowe, G. Poirier, H. Friis, K. Helwig","doi":"10.5194/ejm-35-143-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-143-2023","url":null,"abstract":"Abstract. The new mckelveyite group mineral alicewilsonite-(YCe),\u0000ideally Na2Sr2YCe(CO3)6 ⋅ 3H2O, was found\u0000at Mont Saint-Hilaire, Quebec, Canada, and subsequently at the Saint-Amable\u0000sill, Quebec, Canada, and the Khibiny Massif, Kola Peninsula, Russia.\u0000Alicewilsonite-(YCe) crystals are commonly hemimorphic pseudotrigonal and\u0000pseudohexagonal and show barrel-shaped, saucer-shaped, spindle-shaped,\u0000cone-shaped, columnar, tabular, and platy habits. They are usually up to 2–3 mm in size with some larger crystals reaching 2–3 cm. The crystals often\u0000form stacked or parallel growth aggregates and rosettes.\u0000Alicewilsonite-(YCe) colour varies from pale yellow to yellow, lemon yellow,\u0000green yellow, orange-yellow, pale green to green, pale grey to grey, green\u0000grey, beige, and colourless. The streak is white; the lustre is vitreous.\u0000The cleavage is fair to indistinct, parallel to (001). The Mohs hardness is\u00003. Dcalc is 3.37 g cm−3. Alicewilsonite-(YCe) is optically biaxial\u0000(+), with α=1.554(3), β=1.558(3), γ=1.644(2), 2V (calc.) = 26∘, 2V (meas.) = 20(3)∘ (589 nm).\u0000The IR spectrum is reported. The\u0000composition (wt %, average of six analyses) is Na2O 7.42, CaO 0.72,\u0000SrO 21.49, BaO 1.41, Y2O3 8.52, La2O3 5.93,\u0000Ce2O3 9.52, Pr2O3 0.59, Nd2O3 1.75,\u0000Sm2O3 0.46, Gd2O3 0.83, Dy2O3 1.65,\u0000Ho2O3 0.34, Er2O3 1.21, Yb2O3 0.64, CO2\u000029.33, H2O 6.13, total 97.94. The empirical formula of the holotype\u0000calculated on the basis of six cations is\u0000Na2.11Ca0.11Sr1.83Ba0.08Y0.67(Ce0.51La0.32Pr0.03Nd0.09Sm0.02Gd0.04\u0000Dy0.08Ho0.02Er0.06Yb0.03)Σ1.20(CO3)5.88 (H2O)3.00.\u0000The mineral is triclinic,\u0000P1, a=9.0036(6) Å, b=9.0175(6) Å, c=6.7712(5) Å, α=102.724(2)∘, β=116.398(2)∘, γ=60.003(2)∘, V=426.46(5) Å3,\u0000and Z=1. The strongest\u0000reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are\u00006.07(31)(001), 4.372(100)(120, 2‾1‾1, 11‾0), 4.037(25)(1‾11, 1‾2‾1, 210),\u00003.201(25)(121, 2‾1‾2, 11‾1),\u00002.831(67)(1‾12, 1‾2‾2, 211, 1‾21, 21‾0), 2.601(39)(030, 3‾3‾1,3‾01), 2.236(24)(2‾4‾1, 2‾21,\u00004‾2‾1). 2.019(23)(003, 2‾22, 2‾4‾2‾, 420). 1.9742(24)(032, 3‾03,\u00003‾3‾3, 331, 03‾2, 301). The crystal\u0000structure, solved and refined from single-crystal X-ray diffraction data\u0000(R1=0.055), is of the weloganite type.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43803131","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mckelveyite group minerals – Part 1: Nomenclature and new data on donnayite-(Y)","authors":"I. Lykova, R. Rowe, G. Poirier, G. Giester, Kelsie Ojaste, H. Friis","doi":"10.5194/ejm-35-133-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-133-2023","url":null,"abstract":"Abstract. The mckelveyite group consisting of seven carbonate\u0000minerals – mckelveyite-(Y), ewaldite, weloganite, donnayite-(Y),\u0000alicewilsonite-(YCe), alicewilsonite-(YLa), and bainbridgeite-(YCe) – is\u0000formally established. The general formula of the minerals is\u0000A3B3(CO3)6 ⋅ 3H2O, where A= Na, Ca, Y, and Zr\u0000and B= Sr, Ba, Ce, and La. Different order–disorder modifications are known\u0000resulting in triclinic, monoclinic, hexagonal, and trigonal minerals with\u0000essentially the same structure. Re-examination of donnayite-(Y) type\u0000specimens shows that the original description contains data collected on two\u0000different species: donnayite-(Y) and alicewilsonite-(YCe). Donnayite-(Y),\u0000NaCaSr3Y(CO3)6 ⋅ 3H2O, was found in only one\u0000specimen out of seven – CMNMC 39396 – housed at the Canadian Museum of\u0000Nature, Ottawa. This specimen becomes the holotype of donnayite-(Y). The\u0000crystal structure of donnayite-(Y) was solved and refined to R1= 0.055 for 3366 reflections with I>2σ(I). Donnayite-(Y) is\u0000shown to have a weloganite-type structure confirming its place in the\u0000mckelveyite group.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49580136","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CO2 diffusion in dry and hydrous leucititic melt","authors":"Lennart Koch, B. Schmidt","doi":"10.5194/ejm-35-117-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-117-2023","url":null,"abstract":"Abstract. Using the diffusion couple technique, diffusion of\u0000CO2 in a leucititic melt from the Colli Albani Volcanic District in\u0000Italy was investigated at temperatures between 1200 and 1350 ∘C\u0000in an internally heated pressure vessel at 300 MPa. To examine the effect of\u0000dissolved H2O in the melt, experiments were performed for a nominally\u0000dry melt (0.18 ± 0.03 wt % H2O) and for a hydrous melt\u0000containing 3.36 ± 0.28 wt % H2O. Diffusion experiments were run\u0000for 40 to 120 min and terminated by rapid quench. CO2 concentration\u0000profiles were subsequently measured via attenuated total reflection\u0000Fourier transform infrared spectroscopy (ATR-FTIR) and fitted with error\u0000functions to obtain individual diffusion coefficients. For the anhydrous and hydrous sample series, seven diffusion coefficients\u0000were determined each. Diffusivity was found to increase exponentially with\u0000temperature for both melts following an Arrhenius behaviour. The Arrhenius\u0000equation for the nominally dry leucititic melt is described by log⁡DCO2=-1.44(±0.24)⋅10000T-1.95(±1.59), where DCO2 is the diffusion coefficient in m2 s−1 and T is the\u0000temperature in K. In the experimental temperature range, H2O has an\u0000accelerating effect on CO2 diffusion. At 1200 ∘C,\u0000diffusivity increases from 1.94 × 10−12 m2 s−1 in\u0000the dry melt to 1.54 × 10−11 m2 s−1 in the hydrous\u0000melt. The Arrhenius equation for the leucititic melt containing 3.36±0.28 wt % H2O is given by log⁡DCO2=-1.09(±0.30)⋅10000T-3.41(±1.99). The activation energies for CO2 were determined to be 275 ± 47 kJ mol−1 for the anhydrous melt and 209 ± 58 kJ mol−1 for the\u0000hydrous melt. The high CO2 activation energy in the leucititic melt indicates that\u0000the diffusion might be partly attributed to the carbonate species. At high\u0000magmatic temperatures above 1200 ∘C, CO2 diffusivity in the\u0000leucititic melt is only slightly lower than CO2 diffusion in rhyolitic\u0000and basaltic melts, suggesting that CO2 diffusion in natural melts is\u0000relatively independent from the bulk melt composition at such temperatures.\u0000CO2 diffuses slower than other volatile components such as halogens and\u0000H2O in depolymerized silicate melts. Thus, a fractionation of volatiles\u0000can occur during magma ascent and degassing. The experimental data on\u0000CO2 diffusion can be used for modelling the degassing mechanisms of\u0000ultrapotassic mafic melts.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45155594","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of Fe–Fe interactions and X-site vacancy ordering on the OH-stretching spectrum of foitite","authors":"E. Balan, G. Radtke, C. Fourdrin, L. Paulatto, H. A. Horn, Y. Fuchs","doi":"10.5194/ejm-35-105-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-105-2023","url":null,"abstract":"Abstract. The OH-stretching infrared absorption spectrum of a tourmaline sample close\u0000to the foitite end-member is interpreted in the light of the density\u0000functional theory (DFT) modeling of iron-bearing Y3Z6 clusters in\u0000tourmaline. The iron-bearing clusters reflect the Al-rich and Na-deficient\u0000character of foitite and contain either two Fe2+ and one Al3+ or\u0000one Fe2+ and two Al3+ ions at the Y sites. The clusters are\u0000embedded in a tourmaline host structure with dravite composition. For the\u0000iron dimer models, the structural and vibrational properties corresponding\u0000to the ferromagnetic (FM) or anti-ferromagnetic (AFM) arrangement of the\u0000iron spins and the effect of vacancy ordering along the [001] axis are\u0000considered. A significant difference in the relaxed structure of the FM and\u0000AFM clusters is observed, stemming from the electron delocalization and\u0000Fe–Fe bonding interactions in the FM cluster. These bonding interactions are\u0000not allowed in the AFM cluster. In this case, the valence electrons with\u0000opposite spins remain separately localized on the two Fe atoms. The AFM\u0000configuration is more stable than the FM one in the theoretical models,\u0000provided that the description of the on-site Coulomb repulsion in Fe(3d)\u0000orbitals is improved within the DFT + U framework. Based on the theoretical\u0000results, the two bands at 3630 and 3644 cm−1 in the vibrational spectra\u0000of iron-rich and Na-deficient tourmalines are assigned to WOH groups\u0000associated with YFe22+YAl3+ environments with an\u0000AFM coupling of Fe ions and surrounded by one and two vacant X sites,\u0000respectively. The two major VOH bands of the experimental spectrum are\u0000interpreted on the same basis, and these interpretations are extrapolated to\u0000Mn-bearing tourmalines.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49237599","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Whiteite-(CaMnFe), a new jahnsite-group mineral from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria","authors":"R. Hochleitner, Christian Rewitzer, I. Grey, W. G. Mumme, C. MacRae, A. R. Kampf, E. Keck, R. Gable, A. Glenn","doi":"10.5194/ejm-35-95-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-95-2023","url":null,"abstract":"Abstract. Whiteite-(CaMnFe),\u0000CaMn2+Fe22+Al2(PO4)4(OH)2 ⋅ 8H2O, is a new whiteite-subgroup member of the jahnsite group from the\u0000Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany. It was found in\u0000vugs in an altered feldspar area of a specimen composed predominantly of\u0000rockbridgeite, with hureaulite and relic triphylite. Other associated\u0000minerals in small vugs in the specimen were strengite and laueite.\u0000Whiteite-(CaMnFe) occurs as sprays and clusters of colourless to pale\u0000yellow, rod-like crystals, with diameters of typically 10 to 50 µm\u0000and lengths up to ∼ 500 µm. The crystals are flattened\u0000on {001} and elongated along [010]. The measured\u0000density is 2.80(2) g cm−3. Optically, whiteite-(CaMnFe)\u0000crystals are biaxial (+), with α=1.608(3), β=1.612(3), γ=1.624(3) and 2V(meas.) = 59(1)∘. The\u0000empirical formula from electron microprobe analyses and structure refinement\u0000is\u0000(Ca0.70Mn0.30)Mn(Fe1.232+Mn0.49Mg0.29Zn0.06)(Al1.88Fe0.123+)(PO4)3.96(OH)2(H2O)8.\u0000Whiteite-(CaMnFe) is monoclinic, P2 /a, a=14.925(5), b=7.0100(14), c=10.053(2) Å, β=111.31(2)∘, V=979.9(4) Å3 and Z=2. The crystal structure was refined using\u0000single-crystal data to wRobs=0.052 for 1613 reflections with I>3σ(I). Site occupancy refinements confirm the ordering\u0000of dominant Ca, Mn and Fe2+ in the X, M1 and M2 sites, respectively, of\u0000the general jahnsite-group formula\u0000XM1M22M32(H2O)8(OH)2(PO4)4.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49035447","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}