Abstract. A natural sample of Fe-bearing paramontroseite (V0.84Fe0.19Al0.03O2; a = 4.8960(14), b = 9.395(3), c = 2.9163(5) Å, V = 134.14(6) Å3; space group Pbnm) from Prachovice mine (Czech Republic) was investigated to shed light on cation partitioning and behavior upon heating. XRD experiments showed that V and Fe are not vicariant of one another, as V occupies the octahedral site at (0.09, 0.14, 0.25), whereas Fe enters a tetrahedral site at (0.41, 0.06, 0.25), the latter expected to be empty in the ideal structure. Thermal expansion is anisotropic, leading to the following β coefficients: -2.0×10-5, 3.0×10-5, 0.8×10-5 and 1.8×10-5 ∘C−1 for a, b, c and V, respectively. At T higher than 350 ∘C, V undergoes oxidation, from [4+] to [5+], and paramontroseite decomposes into Fe-tetrapolyvanadate (Fe2V4O13) and V-pentoxide (V2O5). µ-Raman spectroscopy analyses confirmed that paramontroseite is sensitive to heating: the crystal surface invested by the laser beam degrades very quickly, leading to the phases revealed by diffraction measurements. There is no evidence for the formation at high T of a rutile-type phase, as we observed for iso-structural ramsdellite MnO2.
摘要含铁副斜长辉石(v0.84 fe0.19 al0.030 o2;= 4.8960 (14), b = 9.395 (3), c = 2.9163 (5), V = 134.14 (6) A3;研究了来自捷克共和国prachovice矿的空间群Pbnm)，以揭示其在加热时的阳离子分配和行为。XRD实验表明，在理想结构中，V和Fe不是相互替换的，V在(0.09,0.14,0.25)处占据八面体位置，而Fe在(0.41,0.06,0.25)处进入四面体位置，四面体位置为空。热膨胀是各向异性的，导致β系数如下:-2.0×10-5, 3.0×10-5, 0.8×10-5 and1.8×10-5对a, b, C和V分别是C−1。在T大于350°C时，V发生从[4+]到[5+]的氧化，副斜锰矿分解成四多钒酸铁(Fe2V4O13)和五氧化钒(V2O5)。微拉曼光谱分析证实，顺滑石对加热很敏感:激光束注入的晶体表面降解得非常快，导致衍射测量显示的相。没有证据表明在高温度下形成金红石型相，而我们在等结构的ramsdellite MnO2中观察到这一点。
{"title":"Fe-bearing vanadium dioxide–paramontroseite: structural details and high-temperature transformation","authors":"N. Curetti, A. Pavese","doi":"10.5194/ejm-35-373-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-373-2023","url":null,"abstract":"Abstract. A natural sample of Fe-bearing paramontroseite\u0000(V0.84Fe0.19Al0.03O2; a = 4.8960(14), b = 9.395(3),\u0000c = 2.9163(5) Å, V = 134.14(6) Å3; space group Pbnm) from\u0000Prachovice mine (Czech Republic) was investigated to shed light on cation\u0000partitioning and behavior upon heating. XRD experiments showed that V and Fe\u0000are not vicariant of one another, as V occupies the octahedral site at (0.09, 0.14, 0.25), whereas Fe enters a tetrahedral site at (0.41, 0.06, 0.25), the\u0000latter expected to be empty in the ideal structure. Thermal expansion is\u0000anisotropic, leading to the following β coefficients: -2.0×10-5, 3.0×10-5, 0.8×10-5 and\u00001.8×10-5 ∘C−1 for a, b, c and V,\u0000respectively. At T higher than 350 ∘C, V undergoes oxidation, from\u0000[4+] to [5+], and paramontroseite decomposes into Fe-tetrapolyvanadate\u0000(Fe2V4O13) and V-pentoxide (V2O5). µ-Raman\u0000spectroscopy analyses confirmed that paramontroseite is sensitive to heating:\u0000the crystal surface invested by the laser beam degrades very quickly,\u0000leading to the phases revealed by diffraction measurements. There is no\u0000evidence for the formation at high T of a rutile-type phase, as we observed\u0000for iso-structural ramsdellite MnO2.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":"1 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71223816","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}
Yanjuan Wang, F. Nestola, Huai-kun Li, Z. Hou, M. Pamato, D. Novella, Alessandra Lorenzetti, Pia Antonietta Antignani, P. Cornale, J. Nava, G. Dong, Kai Qu
Abstract. We have investigated a suite of natural diamonds from the kimberlite pipe of the Changma Kimberlite Belt, Mengyin County, Shandong Province, China, with the aim of constraining pressures and temperatures of formation. Here we report the non-destructive investigation of an olivine inclusion still entrapped within a lithospheric diamond by single-crystal X-ray diffraction. We were able to refine anisotropically its crystal structure to R1= 1.42 % using ionized scattering curves; this allows estimation of the composition of the olivine as Mg1.82Fe0.18SiO4. This composition corresponds to a calculated unit-cell volume equal to V= 292.70 Å3 at room temperature and pressure. We have validated the above-calculated composition and unit-cell volume by releasing the inclusion from the diamond host, resulting in a consistent composition calculated using non-destructive methods of Mg1.84Fe0.16SiO4 and V= 292.80 ± 0.07 Å3. Considering that the unit-cell volume of the olivine still inside its diamond host is V= 289.7 ± 0.2 Å3, we calculated a residual pressure Pinc= 1.4 ± 0.1 GPa with respect to the released crystal and Pinc= 1.3 ± 0.2 GPa with respect to the volume calculated from the “composition” indirectly retrieved by the structure refinement under ambient conditions. The two values of Pinc overlap within experimental uncertainty. We performed Fourier transform infrared (FTIR) analysis on the diamond host in order to calculate its mantle residence temperature, Tres, which resulted in a value of 1189 ∘C (for an assumed diamond age of 3 Ga) and 1218 ∘C (for an age of 1 Ga), with an average Tres equal to 1204 ± 15 ∘C. Using the most up-to-date pressure–volume–temperature equations of state for olivine and diamond, the residual pressure Pinc= 1.4 ± 0.1 GPa and average residence temperature of the diamond host Tres= 1204 ∘C, we retrieved a pressure of entrapment Ptrap= 6.3 ± 0.4 GPa. Using the non-destructive approach and relative Pinc = 1.3 GPa, we obtained a perfectly overlapping Ptrap= 6.2 GPa, within experimental uncertainty. This entrapment pressure corresponds to depths of about 190 ± 12 km. These results demonstrate that for high-quality crystal structure data measured on inclusions still trapped within diamond hosts, even a non-destructive approach can be used to calculate the depth of formation of diamond–olivine pairs. In terms of geological implications, the results from this work show that Changma diamonds formed under a conductive geotherm lying between 35 and 40 mW m−2, at a depth of about 190 km. This value lies within the recently reported upper limit of the average depth of formation of worldwide lithospheric diamonds, which is 175 ± 15 km and is in agreement with P–T data obtained in the literature from kimberlite xenoliths.
{"title":"In situ single-crystal X-ray diffraction of olivine inclusion in diamond from Shandong, China: implications for the depth of diamond formation","authors":"Yanjuan Wang, F. Nestola, Huai-kun Li, Z. Hou, M. Pamato, D. Novella, Alessandra Lorenzetti, Pia Antonietta Antignani, P. Cornale, J. Nava, G. Dong, Kai Qu","doi":"10.5194/ejm-35-361-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-361-2023","url":null,"abstract":"Abstract. We have investigated a suite of natural diamonds from the\u0000kimberlite pipe of the Changma Kimberlite Belt, Mengyin County, Shandong\u0000Province, China, with the aim of constraining pressures and temperatures of\u0000formation. Here we report the non-destructive investigation of an olivine\u0000inclusion still entrapped within a lithospheric diamond by single-crystal\u0000X-ray diffraction. We were able to refine anisotropically its crystal\u0000structure to R1= 1.42 % using ionized scattering curves; this\u0000allows estimation of the composition of the olivine as\u0000Mg1.82Fe0.18SiO4. This composition corresponds to a\u0000calculated unit-cell volume equal to V= 292.70 Å3 at room\u0000temperature and pressure. We have validated the above-calculated composition\u0000and unit-cell volume by releasing the inclusion from the diamond host,\u0000resulting in a consistent composition calculated using non-destructive\u0000methods of Mg1.84Fe0.16SiO4 and V= 292.80 ± 0.07 Å3. Considering that the unit-cell volume of the olivine still\u0000inside its diamond host is V= 289.7 ± 0.2 Å3, we calculated\u0000a residual pressure Pinc= 1.4 ± 0.1 GPa with respect to the\u0000released crystal and Pinc= 1.3 ± 0.2 GPa with respect to the\u0000volume calculated from the “composition” indirectly retrieved by the\u0000structure refinement under ambient conditions. The two values of Pinc\u0000overlap within experimental uncertainty. We performed Fourier transform infrared (FTIR) analysis on the\u0000diamond host in order to calculate its mantle residence temperature,\u0000Tres, which resulted in a value of 1189 ∘C (for an assumed\u0000diamond age of 3 Ga) and 1218 ∘C (for an age of 1 Ga), with an\u0000average Tres equal to 1204 ± 15 ∘C. Using the most up-to-date pressure–volume–temperature equations of state for\u0000olivine and diamond, the residual pressure Pinc= 1.4 ± 0.1 GPa\u0000and average residence temperature of the diamond host Tres= 1204 ∘C, we retrieved a pressure of entrapment Ptrap= 6.3 ± 0.4 GPa. Using the non-destructive approach and relative Pinc = 1.3 GPa, we obtained a perfectly overlapping Ptrap= 6.2 GPa,\u0000within experimental uncertainty. This entrapment pressure corresponds to\u0000depths of about 190 ± 12 km. These results demonstrate that for\u0000high-quality crystal structure data measured on inclusions still trapped\u0000within diamond hosts, even a non-destructive approach can be used to\u0000calculate the depth of formation of diamond–olivine pairs. In terms of\u0000geological implications, the results from this work show that Changma\u0000diamonds formed under a conductive geotherm lying between 35 and 40 mW m−2, at a depth of about 190 km. This value lies within the recently\u0000reported upper limit of the average depth of formation of worldwide\u0000lithospheric diamonds, which is 175 ± 15 km and is in agreement with\u0000P–T data obtained in the literature from kimberlite xenoliths.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46705032","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}
L. Barale, G. Capitani, P. Castello, R. Compagnoni, R. Cossio, G. Fiore, L. Pastero, M. Mellini
Abstract. The ultramafic body of Monte Avic (Aosta Valley, Western Alps, Italy) consists of antigorite serpentinite and Ti-clinohumite metadunite. They host late metamorphic veins, up to a couple of centimeters thick, compact, and homogeneous, with a “porcelain” appearance. Vein colors range from yellowish to light greenish, light yellowish fading to white, or rare orange. The veins consist of 15-sector PS-15 polygonal serpentine, with chemical composition Mg2.85 Fe0.08 Si2.05 O7.05 [OH]3.95. Recognition of this unusual phase is supported by diagnostic satellite reflections in the X-ray powder diffraction pattern (e.g., at dobs of 2.502, 2.336, 2.151, and 1.966 Å) TEM images (showing 15-sector polygonal fibers, mostly 200 nm in diameter and a few µm in length, forming a randomly oriented felt) and a µ-Raman wavenumber, matching previous data. This different evidence affords the successful distinction of PS-15 and PS-30, alternatively using TEM images, X-ray powder diffraction, or the low- and high-wavenumber µ-Raman spectra. At Monte Avic, the vein emplacement was accompanied by significant fluid pressure, as suggested by deformation and dismembering of the host rock, with PS-15 grown within isotropic stress microenvironments characterized by fluid-filled voids. Random growth of the mass-fiber polygonal serpentine was favored by low-strain conditions. PS-15 veins formed at the end of the long polyphase Alpine orogenic evolution, with hydrous fluids possibly deriving from serpentinite dehydration in the depth.
{"title":"Late metamorphic veins with dominant PS-15 polygonal serpentine in the Monte Avic ultramafite","authors":"L. Barale, G. Capitani, P. Castello, R. Compagnoni, R. Cossio, G. Fiore, L. Pastero, M. Mellini","doi":"10.5194/ejm-35-347-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-347-2023","url":null,"abstract":"Abstract. The ultramafic body of Monte Avic (Aosta Valley, Western Alps,\u0000Italy) consists of antigorite serpentinite and Ti-clinohumite metadunite.\u0000They host late metamorphic veins, up to a couple of centimeters thick,\u0000compact, and homogeneous, with a “porcelain” appearance. Vein colors range\u0000from yellowish to light greenish, light yellowish fading to white, or rare\u0000orange. The veins consist of 15-sector PS-15 polygonal serpentine,\u0000with chemical composition Mg2.85 Fe0.08 Si2.05 O7.05\u0000[OH]3.95. Recognition of this unusual phase is supported by diagnostic\u0000satellite reflections in the X-ray powder diffraction pattern (e.g., at\u0000dobs of 2.502, 2.336, 2.151, and 1.966 Å) TEM images (showing\u000015-sector polygonal fibers, mostly 200 nm in diameter and a few µm in\u0000length, forming a randomly oriented felt) and a µ-Raman wavenumber,\u0000matching previous data. This different evidence affords the successful\u0000distinction of PS-15 and PS-30, alternatively using TEM images, X-ray powder\u0000diffraction, or the low- and high-wavenumber µ-Raman spectra. At Monte\u0000Avic, the vein emplacement was accompanied by significant fluid pressure, as\u0000suggested by deformation and dismembering of the host rock, with PS-15 grown\u0000within isotropic stress microenvironments characterized by fluid-filled\u0000voids. Random growth of the mass-fiber polygonal serpentine was favored by\u0000low-strain conditions. PS-15 veins formed at the end of the long polyphase\u0000Alpine orogenic evolution, with hydrous fluids possibly deriving from\u0000serpentinite dehydration in the depth.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46794704","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}
Abstract. A new occurrence of pyrite crystals with rhombohedral habit, up to several centimeters in length, is described from the Madan Pb–Zn ore field (Rhodope Massif, south Bulgaria), where it constitutes a late pyrite generation. As observed in the past in other deposits, the ideal rhombohedron is derived from the pyritohedron by suppression of half of its faces (six “polar faces”) around a ternary axis. In studied crystals, together with six main “equatorial faces”, additional minor faces correspond to cube faces as well as polar faces. Such a dissymmetry indicates that the crystallographic point group of these crystals is 3‾, a subgroup of the eigensymmetry 3‾2/m of a rhombohedron taken as geometric face form. Twinning by metric merohedry confirms such a symmetry decrease and permits the definition of this type of pyrite as a dimorph of cubic pyrite, i.e., pseudo-cubic trigonal pyrite (pyrite-R). Twin operations belong to the set of symmetry operations absent in point group 3‾ relative to pyrite symmetry m3‾: reflection about the {100} plane or two-fold rotation about the <100> direction. Four twin types have been distinguished (name, chromatic point group): three contact twins (reflection, m′; rotation, 2′; trapezoidal, (m(2)m(2)2(2))(4)), as well as one penetration twin (crossed, 2′/m′). Composition planes always correspond to {100}, but there are two types of twin interfaces. More complex twinned samples may develop erratically during crystal growth. Other twin variations as well as genetic aspects of such a type of pyrite are discussed.
{"title":"Pseudo-cubic trigonal pyrite from the Madan Pb–Zn ore field (Rhodope Massif, Bulgaria): morphology and twinning","authors":"Y. Moëlo","doi":"10.5194/ejm-35-333-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-333-2023","url":null,"abstract":"Abstract. A new occurrence of pyrite crystals with rhombohedral\u0000habit, up to several centimeters in length, is described from the Madan Pb–Zn\u0000ore field (Rhodope Massif, south Bulgaria), where it constitutes a late\u0000pyrite generation. As observed in the past in other deposits, the ideal\u0000rhombohedron is derived from the pyritohedron by suppression of half of its\u0000faces (six “polar faces”) around a ternary axis. In studied crystals,\u0000together with six main “equatorial faces”, additional minor faces\u0000correspond to cube faces as well as polar faces. Such a dissymmetry\u0000indicates that the crystallographic point group of these crystals is\u00003‾, a subgroup of the eigensymmetry 3‾2/m of a rhombohedron\u0000taken as geometric face form. Twinning by metric merohedry confirms such a\u0000symmetry decrease and permits the definition of this type of pyrite as a dimorph of\u0000cubic pyrite, i.e., pseudo-cubic trigonal pyrite (pyrite-R). Twin operations\u0000belong to the set of symmetry operations absent in point group 3‾\u0000relative to pyrite symmetry m3‾: reflection about the {100} plane or two-fold rotation about the <100> direction. Four twin types have been distinguished (name,\u0000chromatic point group): three contact twins (reflection, m′; rotation, 2′;\u0000trapezoidal, (m(2)m(2)2(2))(4)), as well as one penetration twin\u0000(crossed, 2′/m′). Composition planes always correspond to {100}, but there are two types of twin interfaces. More\u0000complex twinned samples may develop erratically during crystal growth. Other\u0000twin variations as well as genetic aspects of such a type of pyrite are\u0000discussed.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46213374","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}
Shashank Prabha-Mohan, K. Koga, A. Mathieu, Franck Pointud, D. Narvaez
Abstract. In this paper, we present a new design for a 1 atm gas-mixing furnace using the gas mixture CO–CO2–SO2. This furnace can simulate disequilibrium processes such as magmatic and volcanic degassing. Here, we present the technical aspects of the design. The furnace can sustain temperatures of up to 1650 ∘C and has a hot zone that spans 200 mm vertically, where the hotspot is determined to be ∼ 32 mm below the midpoint of the furnace enclosure. The four mass flow controllers are individually calibrated and accurate to within 0.8 % of the specified value. The fO2 is accurately reproduced in the furnace within ±0.002 log units, as calibrated by the Fe–FeO reaction across the iron–wüstite (IW) buffer at 1300 ∘C. The furnace can reliably simulate dynamic conditions, where the fO2 can be modulated at a maximum rate of 2.0 log units min−1 by varying the gas mixture. A delay of 40 s is observed to attain the fO2 calculated from the gas mixture, at the hotspot. A series of safety measures to protect the user from exposure to the toxic gases are detailed. In our experiments, the furnace is used to determine sulfur isotope fractionation factors among melt, sulfide, and the gas phase, within a magmatic context, using either crystals of olivine or silica glass tubes. The furnace has the potential to investigate various other dynamic high-temperature reactions occurring on Earth.
{"title":"One-atmosphere high-temperature CO–CO2–SO2 gas-mixing furnace: design, operation, and applications","authors":"Shashank Prabha-Mohan, K. Koga, A. Mathieu, Franck Pointud, D. Narvaez","doi":"10.5194/ejm-35-321-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-321-2023","url":null,"abstract":"Abstract. In this paper, we present a new design for a 1 atm gas-mixing furnace using the gas mixture CO–CO2–SO2. This furnace can simulate disequilibrium processes such as magmatic and volcanic degassing. Here, we present the technical aspects of the design. The furnace can sustain temperatures of up to 1650 ∘C and has a hot zone that spans 200 mm vertically, where the hotspot is determined to be ∼ 32 mm below the midpoint of the furnace enclosure. The four mass flow controllers are individually calibrated and accurate to within 0.8 % of the specified value. The fO2 is accurately reproduced in the furnace within ±0.002 log units, as calibrated by the Fe–FeO reaction across the iron–wüstite (IW) buffer at 1300 ∘C. The furnace can reliably simulate dynamic conditions, where the fO2 can be modulated at a maximum rate of 2.0 log units min−1 by varying the gas mixture. A delay of 40 s is observed to attain the fO2 calculated from the gas mixture, at the hotspot. A series of safety measures to protect the user from exposure to the toxic gases are detailed. In our experiments, the furnace is used to determine sulfur isotope fractionation factors among melt, sulfide, and the gas phase, within a magmatic context, using either crystals of olivine or silica glass tubes. The furnace has the potential to investigate various other dynamic high-temperature reactions occurring on Earth.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47479064","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}
Abstract. The coexistence of chloritoid and biotite in medium-pressure Barrovian terranes is quite uncommon, and the parameters controlling their equilibrium relations are still controversial. Various studies have already investigated the influence of pressure (P), temperature (T), bulk rock (X bulk) and fluid (X fluid) compositions on the stability of this assemblage. Here we apply forward thermodynamic modelling on amphibolite-facies metapelites from the upper portion of the Lesser Himalayan Sequence (eastern Nepal Himalaya) to test which parameters mostly influence the stability of the chloritoid + biotite assemblage. P–T isochemical phase diagrams calculated in the MnNKCFMASHTO system fail in reproducing the coexistence of chloritoid and biotite, predicting biotite appearance at higher temperatures than chloritoid breakdown. Neither the fluid composition (i.e. reduced H2O activity due to the presence of CO2) nor a more oxidated state of the system favours their coexistence, while slightly H2O-undersaturated conditions expand the biotite stability field toward lower temperatures, allowing the development of the chloritoid + biotite assemblage. Kinetic factors could have further contributed to the stability of this assemblage: thermal overstepping of the chloritoid-consuming and staurolite-producing reaction, induced by the difficulty in the staurolite nucleation and/or by the sluggishness of chloritoid dissolution, could have enhanced the metastable persistence of chloritoid at temperatures compatible with the presence of biotite. Being the kinetics efficiency intrinsically linked to the degree of fluid availability, the two factors (i.e. H2O-undersaturated conditions and kinetics of the chloritoid-consuming reaction) were likely complementary rather than mutually exclusive.
{"title":"Equilibrium and kinetic approaches to understand the occurrence of the uncommon chloritoid + biotite assemblage","authors":"S. Nerone, C. Groppo, F. Rolfo","doi":"10.5194/ejm-35-305-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-305-2023","url":null,"abstract":"Abstract. The coexistence of chloritoid and biotite in medium-pressure Barrovian\u0000terranes is quite uncommon, and the parameters controlling their equilibrium\u0000relations are still controversial. Various studies have already investigated\u0000the influence of pressure (P), temperature (T), bulk rock (X bulk) and fluid\u0000(X fluid) compositions on the stability of this assemblage. Here we apply\u0000forward thermodynamic modelling on amphibolite-facies metapelites from the\u0000upper portion of the Lesser Himalayan Sequence (eastern Nepal Himalaya) to\u0000test which parameters mostly influence the stability of the chloritoid + biotite assemblage. P–T isochemical phase diagrams calculated in the\u0000MnNKCFMASHTO system fail in reproducing the coexistence of chloritoid and\u0000biotite, predicting biotite appearance at higher temperatures than\u0000chloritoid breakdown. Neither the fluid composition (i.e. reduced H2O\u0000activity due to the presence of CO2) nor a more oxidated state of the\u0000system favours their coexistence, while slightly H2O-undersaturated\u0000conditions expand the biotite stability field toward lower temperatures,\u0000allowing the development of the chloritoid + biotite assemblage. Kinetic\u0000factors could have further contributed to the stability of this assemblage:\u0000thermal overstepping of the chloritoid-consuming and staurolite-producing\u0000reaction, induced by the difficulty in the staurolite nucleation and/or by\u0000the sluggishness of chloritoid dissolution, could have enhanced the\u0000metastable persistence of chloritoid at temperatures compatible with the\u0000presence of biotite. Being the kinetics efficiency intrinsically linked to\u0000the degree of fluid availability, the two factors (i.e.\u0000H2O-undersaturated conditions and kinetics of the chloritoid-consuming\u0000reaction) were likely complementary rather than mutually exclusive.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45908849","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}
I. Grey, R. Hochleitner, A. R. Kampf, Stephanie Boer, C. MacRae, J. Cashion, Christian Rewitzer, W. G. Mumme
Abstract. Manganrockbridgeite, Mn22+Fe33+(PO4)3(OH)4(H2O), is a new member of the rockbridgeite group, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria. It occurs in association with frondelite, kenngottite, hureaulite and hematite. It forms compact intergrowths and clusters of shiny greenish black blades up to 200 µm long and 20 µm wide but only a few micrometres thick. The crystals are elongated on [100] and flattened on {001}, with perfect cleavage parallel to {001}. Individual thin blades are green in transmitted light and red under crossed polars. The calculated density is 3.40 g cm−3. Manganrockbridgeite is biaxial (+/-), with α= 1.795(5), β= 1.805(calc), γ=1.815(5) (white light) and 2V(meas.) = 90(2)∘. The empirical formula from electron microprobe analyses, Mössbauer spectroscopy and crystal structure refinement is (Mn1.072+Fe0.692+Fe0.163+)Σ1.92(Fe3+)2.88(PO4)3(OH)3.64(H2O)1.44. Manganrockbridgeite has monoclinic symmetry with space group P21/m and unit-cell parameters a=5.198(2), b=16.944(5), c=7.451(3) Å, β=110.170(9)∘, V=616.0(4) Å3 and Z=2. The crystal structure was refined using both laboratory and synchrotron single-crystal diffraction data. Whereas other rockbridgeite-group minerals have orthorhombic symmetry with a statistical distribution of 50 % Fe3+ / 50 % vacancies in M3-site octahedra forming face-shared chains along the 5.2 Å axis, monoclinic manganrockbridgeite has full ordering of Fe3+ and vacancies in alternate M3 sites along the 5.2 Å axis.
{"title":"Manganrockbridgeite, Mn2+2Fe3+3(PO4)3(OH)4(H2O), a new member of the rockbridgeite group, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria","authors":"I. Grey, R. Hochleitner, A. R. Kampf, Stephanie Boer, C. MacRae, J. Cashion, Christian Rewitzer, W. G. Mumme","doi":"10.5194/ejm-35-295-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-295-2023","url":null,"abstract":"Abstract. Manganrockbridgeite,\u0000Mn22+Fe33+(PO4)3(OH)4(H2O), is a new\u0000member of the rockbridgeite group, from the Hagendorf-Süd pegmatite,\u0000Oberpfalz, Bavaria. It occurs in association with frondelite, kenngottite,\u0000hureaulite and hematite. It forms compact intergrowths and clusters of shiny\u0000greenish black blades up to 200 µm long and 20 µm wide but only a few micrometres thick. The crystals are elongated on [100] and flattened on\u0000{001}, with perfect cleavage parallel to\u0000{001}. Individual thin blades are green in\u0000transmitted light and red under crossed polars. The calculated density is\u00003.40 g cm−3. Manganrockbridgeite is biaxial (+/-), with\u0000α= 1.795(5), β= 1.805(calc), γ=1.815(5)\u0000(white light) and 2V(meas.) = 90(2)∘. The empirical formula from\u0000electron microprobe analyses, Mössbauer spectroscopy and crystal\u0000structure refinement is\u0000(Mn1.072+Fe0.692+Fe0.163+)Σ1.92(Fe3+)2.88(PO4)3(OH)3.64(H2O)1.44.\u0000Manganrockbridgeite has monoclinic symmetry with space group P21/m and\u0000unit-cell parameters a=5.198(2), b=16.944(5), c=7.451(3) Å,\u0000β=110.170(9)∘, V=616.0(4) Å3 and Z=2.\u0000The crystal structure was refined using both laboratory and synchrotron\u0000single-crystal diffraction data. Whereas other rockbridgeite-group minerals\u0000have orthorhombic symmetry with a statistical distribution of\u000050 % Fe3+ / 50 % vacancies in M3-site octahedra forming face-shared\u0000chains along the 5.2 Å axis, monoclinic manganrockbridgeite has full\u0000ordering of Fe3+ and vacancies in alternate M3 sites along the 5.2 Å\u0000axis.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47757543","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}
Pete Williams, Frédéric Hatert, Marco Pasero, Stuart Mills
{"title":"IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) – Newsletter 72","authors":"Pete Williams, Frédéric Hatert, Marco Pasero, Stuart Mills","doi":"10.5194/ejm-35-285-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-285-2023","url":null,"abstract":"","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135568816","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}
Abstract. To provide a tool for fast estimation of the Fe3+ content in Ca2(Al, Fe3+)3Si3O12(OH) epidote grains, including in thin sections and crude-rock samples, we applied Raman spectroscopy to 33 areas from 15 natural samples with Fe3+ ranging from 0.22 to 1.13 atoms per formula unit (apfu), the chemistry of which was independently determined by wavelength-dispersive electron microprobe analysis (WD-EPMA). The Raman spectra were collected from the very areas subjected to WD-EPMA. We have analysed both the OH-stretching region (3215–3615 cm−1) and the spectral range generated by the framework vibrations (15–1215 cm−1). Similarly to the IR spectra, the Raman peaks in the OH-stretching region shift toward higher wavenumbers with increasing Fe. However, the quantification of Fe3+ based on OH-stretching Raman peaks can be hindered by the multicomponent overlapping and significant intensity variations with the crystal orientation. Among the Raman signals generated by framework vibrations, the position of four peaks (near 250, 570, 600, and 1090 cm−1) exhibit a steady linear regression with the increase in Fe content (in apfu). However, the peak near 250 cm−1 attributed to MO6 vibrations also depends on the crystal orientation and therefore is not always well resolved, which worsens the accuracy in Fe-content determination based on its position. The peaks near 570, 600, and 1090 cm−1 arise from Si2O7 vibrational modes, and although their intensities also vary with the crystal orientation, all three signals are well resolved in a random orientation. However, among the three Si2O7-related signals, the 570 cm−1 peak is the sharpest (peak width <10 cm−1) and is easily recognized as a separate peak. Hence, we propose to use the position of this peak as a highly reliable parameter to estimate the Fe content, via the linear trend given as ω570=577.1(3)-12.7(4)x, where ω is the wavenumber (cm−1) and x is Fe content (apfu), with accuracy ± 0.04 Fe3+ apfu. The peaks near 600 and 1090 cm−1 may be complementarily used for the Fe estimate, based on the following relations: ω600=611.6(2)-13.8(4)x and ω1090=1098.8(3)-13.5(5)x. Analyses of the effect of Sr as a substitution for Ca and Cr at the octahedral sites indicate that contents of Sr <0.12 apfu do not interfere with the quantification of Fe via the ω570 (x) relation, whereas Cr >0.16 apfu leads to overestimation of Fe; Cr presence can be recognized however by the broadening of the peaks near 95 and 250 cm−1.
{"title":"Optimal Raman-scattering signal for estimating the Fe3+ content on the clinozoisite–epidote join","authors":"M. Nagashima, B. Mihailova","doi":"10.5194/ejm-35-267-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-267-2023","url":null,"abstract":"Abstract. To provide a tool for fast estimation of the Fe3+\u0000content in Ca2(Al, Fe3+)3Si3O12(OH) epidote grains,\u0000including in thin sections and crude-rock samples, we applied Raman\u0000spectroscopy to 33 areas from 15 natural samples with Fe3+ ranging from\u00000.22 to 1.13 atoms per formula unit (apfu), the chemistry of which was\u0000independently determined by wavelength-dispersive electron microprobe\u0000analysis (WD-EPMA). The Raman spectra were collected from the very areas\u0000subjected to WD-EPMA. We have analysed both the OH-stretching region\u0000(3215–3615 cm−1) and the spectral range generated by the framework\u0000vibrations (15–1215 cm−1). Similarly to the IR spectra, the Raman peaks\u0000in the OH-stretching region shift toward higher wavenumbers with increasing\u0000Fe. However, the quantification of Fe3+ based on OH-stretching Raman\u0000peaks can be hindered by the multicomponent overlapping and significant\u0000intensity variations with the crystal orientation. Among the Raman signals\u0000generated by framework vibrations, the position of four peaks (near 250,\u0000570, 600, and 1090 cm−1) exhibit a steady linear regression with the\u0000increase in Fe content (in apfu). However, the peak near 250 cm−1\u0000attributed to MO6 vibrations also depends on the crystal orientation\u0000and therefore is not always well resolved, which worsens the accuracy in\u0000Fe-content determination based on its position. The peaks near 570, 600, and\u00001090 cm−1 arise from Si2O7 vibrational modes, and although\u0000their intensities also vary with the crystal orientation, all three signals\u0000are well resolved in a random orientation. However, among the three\u0000Si2O7-related signals, the 570 cm−1 peak is the sharpest\u0000(peak width <10 cm−1) and is easily recognized as a separate\u0000peak. Hence, we propose to use the position of this peak as a highly\u0000reliable parameter to estimate the Fe content, via the linear trend given as\u0000ω570=577.1(3)-12.7(4)x, where ω is the wavenumber\u0000(cm−1) and x is Fe content (apfu), with accuracy ± 0.04\u0000Fe3+ apfu. The peaks near 600 and 1090 cm−1 may be complementarily\u0000used for the Fe estimate, based on the following relations: ω600=611.6(2)-13.8(4)x and ω1090=1098.8(3)-13.5(5)x. Analyses of\u0000the effect of Sr as a substitution for Ca and Cr at the octahedral sites\u0000indicate that contents of Sr <0.12 apfu do not interfere with the\u0000quantification of Fe via the ω570 (x) relation, whereas Cr\u0000>0.16 apfu leads to overestimation of Fe; Cr presence can be\u0000recognized however by the broadening of the peaks near 95 and 250 cm−1.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41732551","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}
Abstract. The coupling behaviour of H+ and trace elements in rutile has been studied using in situ polarised Fourier transform infrared (FTIR) spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) analysis. H2O contents in rutile can be precisely and accurately quantified from polarised FTIR measurements on single grains in situ. The benefits of this novel approach compared to traditional quantification methods are the preservation of textural context and heterogeneities of water in rutile. Rutile from six different geological environments shows H2O contents varying between ∼ 50–2200 µg g−1, with large intra-grain variabilities for vein-related samples with H2O contents between ∼ 500 and ∼ 2200 µg g−1. From FTIR peak deconvolutions, six distinct OH absorption bands have been identified at ∼ 3280, ∼ 3295, ∼ 3324, ∼ 3345, ∼ 3370, and ∼ 3390 cm−1 that can be related to coupled substitutions with Ti3+, Fe3+, Al3+, Mg2+, Fe2+, and Cr2+, respectively. Rutile from eclogite samples displays the dominant exchange reactions of Ti4+ → Ti3+, Fe3+ + H+, whereas rutile in a whiteschist shows mainly Ti4+ → Al3+ + H+. Trace-element-dependent H+ contents combined with LA–ICP–MS trace-element data reveal the significant importance of H+ for charge balance and trace-element coupling with trivalent cations. Trivalent cations are the most abundant impurities in rutile, and there is not enough H+ and pentavalent cations like Nb and Ta for a complete charge balance, indicating that additionally oxygen vacancies are needed for charge balancing trivalent cations. Valance states of multivalent trace elements can be inferred from deconvoluted FTIR spectra. Titanium occurs at 0.03 ‰–7.6 ‰ as Ti3+, Fe, and Cr are preferentially incorporated as Fe3+ and Cr3+ over Fe2+ and Cr2+, and V most likely occurs as V4+. This opens the possibility of H+ in rutile as a potential indicator of oxygen fugacity of metamorphic and subduction-zone fluids, with the ratio between Ti3+- and Fe3+-related H+ contents being most promising.
{"title":"A framework for quantitative in situ evaluation of coupled substitutions between H+ and trace elements in natural rutile","authors":"Mona Lueder, R. Tamblyn, Jörg Hermann","doi":"10.5194/ejm-35-243-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-243-2023","url":null,"abstract":"Abstract. The coupling behaviour of H+ and trace elements in rutile has been\u0000studied using in situ polarised Fourier transform infrared (FTIR)\u0000spectroscopy and laser ablation inductively coupled plasma mass spectrometry\u0000(LA–ICP–MS) analysis. H2O contents in rutile can be precisely and\u0000accurately quantified from polarised FTIR measurements on single grains in\u0000situ. The benefits of this novel approach compared to traditional\u0000quantification methods are the preservation of textural context and\u0000heterogeneities of water in rutile. Rutile from six different geological\u0000environments shows H2O contents varying between ∼ 50–2200 µg g−1, with large intra-grain variabilities for vein-related samples\u0000with H2O contents between ∼ 500 and\u0000∼ 2200 µg g−1. From FTIR peak deconvolutions, six distinct\u0000OH absorption bands have been identified at ∼ 3280, ∼ 3295, ∼ 3324,\u0000∼ 3345, ∼ 3370, and\u0000∼ 3390 cm−1 that can be related to coupled substitutions\u0000with Ti3+, Fe3+, Al3+, Mg2+, Fe2+, and Cr2+,\u0000respectively. Rutile from eclogite samples displays the dominant exchange\u0000reactions of Ti4+ → Ti3+, Fe3+ + H+, whereas\u0000rutile in a whiteschist shows mainly Ti4+ → Al3+ + H+.\u0000Trace-element-dependent H+ contents combined with LA–ICP–MS\u0000trace-element data reveal the significant importance of H+ for charge\u0000balance and trace-element coupling with trivalent cations. Trivalent cations\u0000are the most abundant impurities in rutile, and there is not enough H+\u0000and pentavalent cations like Nb and Ta for a complete charge balance,\u0000indicating that additionally oxygen vacancies are needed for charge\u0000balancing trivalent cations. Valance states of multivalent trace elements\u0000can be inferred from deconvoluted FTIR spectra. Titanium occurs at 0.03 ‰–7.6 ‰ as Ti3+, Fe, and Cr are preferentially\u0000incorporated as Fe3+ and Cr3+ over Fe2+ and Cr2+, and V\u0000most likely occurs as V4+. This opens the possibility of H+ in rutile as\u0000a potential indicator of oxygen fugacity of metamorphic and subduction-zone\u0000fluids, with the ratio between Ti3+- and Fe3+-related H+\u0000contents being most promising.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2023-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41836087","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}
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