| 1. |
- Ahmed, Engy, et al.
(författare)
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THE MICROBE-MINERAL INTERACTIONS IN THE ACIDIC PODZOL SOIL
- 2013
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Ingår i: Mineralogical magazine. - 0026-461X .- 1471-8022. ; 77:5, s. 564-
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Iron is a key component of the chemical architecture of the biosphere. Due to the low bioavailability of iron in the environment, microorganisms have developed specific uptake strategies, like siderophores, which are operationally defined as low-molecular-mass biogenic Fe(III)-binding compounds, that can increase iron’s bioavailability by promoting the dissolution of iron-bearing minerals. In the present study, we aimed to investigate the composition of hydroxamate siderophores in the soil horizons of the acidic podzol, and study how they are affected by the presence of specific mineral types and microbial communities. Three different minerals (apatite, biotite and oligioclase) were inserted in the soil horizons (O (organic), E (eluvial), B (upper illuvial), and C (mineral)). After two years, soil samples were collected from both the bulk soil (next to the minerals) and from the soil attached to the mineral surfaces. The concentration of ten different fungal tri-hydroxamates and five bacterial ones were determined by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS). In addition, total microbial composition and diversity were studied.Our field experiment succeeded in describing the relationship between the presence of siderophores, soil horizon and mineral type, in addition to understanding the interaction between mineral type and soil microbial composition. A wide range of fungal and bacterial hydroxamates were detected throughout the soil profile. On the other hand, the presence of the minerals completely altered the diversity of siderophores. In addition, each mineral had a unique interaction with hydroxamates in the different soil horizons. There were also a good relationship between the microbial diversity and the siderophore distribution.
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| 2. |
- Ahmed, Engy, et al.
(författare)
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The Role of Microorganisms in the diversity and distribution of siderophores in Podzolic Forest Soil
- 2013
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Ingår i: Mineralogical magazine. - 0026-461X .- 1471-8022. ; 77:2, s. 161--208(48)
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Iron is a key component of the chemical architecture of the biosphere. Due to the low bioavailability of iron in the environment, microorganisms have developed specific uptake strategies. The most important one is the production of siderophores, which are operationally defined as low-molecular-mass biogenic Fe (III)-binding compounds which may greatly increase bioavailability of Fe [1]. One of the primary biogeochemical functions of siderophores is therefore to increase Fe bioavailability by promoting the dissolution of iron-bearing minerals [2]. This study aims to understand the role of microorganisms in the chemical diversity and distribution of siderophores in podzol soil and how this diversity can contribute to the bioavailability of Fe in forest soil.Soil samples were collected from an experimental site in the area of Bispgården in central Sweden (63°07′N, 16°70′E) from the O (organic), E (eluvial), B1 (upper illuvial), and C (mineral) horizons. Concentration and chemical composition of dissolved and adsorbed siderophores in the soil samples were determined using colorimetric assays and high-performance liquid chromatography.The highest siderophore concentrations were found in the O layer and thereafter decreased by depth. Concentrations of dissolved hydroxamate, catecholate and carboxylate siderophores were up to 84, 17 and 0.2 nmol/ g soil, respectively. In contrast, concentrations of adsorbed hydroxamates, catecholates and carboxylates were only up to 1.8, 3 and 0.2 nmol/ g soil, respectively.Siderophore-producing microorganisms were isolated from the same soil samples. Viable fungi, bacteria and actinomycete counts ranged from 7 to 300, from 300 to 1800, and from 0 to 5 cfu/gm, respectively. The highest counts were found in the O and E layers. Only the E layer contained the three types of siderophore-producing microorganisms investigated in this study. Siderophores were extracted from culture filtrates of the isolated microorganisms when grown under iron-limited conditions. These extracts varied considerably in siderophore composition. Fungal isolates produced up to 183 μM of hydroxamates, especially those isolated from the O layer, whereas bacteria and actinomycete isolated from the O and E layers of the soil produced high amounts of carboxylate, catecholate and hydroxamate siderophores. Actinomycete produced up to 93 μM of hydroxamates and 47 μM of catecholates, while bacteria produced up to 34 μM of carboxylates and up to 14 μM of catecholates.The depth variability in concentration and chemical composition and the good correlation between abundance of siderophore-producing microorganisms and siderophore soil concentrations strongly suggest that these siderophore-producing microorganisms play an important role in the mobilization of iron in the podzol soil that may be important in iron availability to plants in forest environment.[1] Clay et al. (1981) Biochemistry 20, 2432-2436. [2] Duckworth et al. (2009) ChemGeol 260, 149-158.
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| 3. |
- Altieri, Alessandra, et al.
(författare)
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Blue growth zones caused by Fe2+ in tourmaline crystals from the San Piero in Campo gem-bearing pegmatites, Elba Island, Italy
- 2022
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 86:6, s. 910-919
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Tidskriftsartikel (refereegranskat)abstract
- Two tourmaline crystals with a blue growth zone at the analogous pole, respectively from the San Silvestro and the Fucili pegmatites, located in the San Piero in Campo village, Elba Island (Tyrrhenian Sea, Italy), have been described for the first time using compositional and spectroscopic data to define their crystal-chemical aspects and the causes of the colour. Compositional data obtained by electron microprobe analysis indicate that both tourmalines belong to the elbaite–fluor-elbaite series. The upper part of each crystal is characterised by an increased amount of Fe (FeO up to ~1 wt.%) and a Ti content below the detection limit. Optical absorption spectra recorded on the blue zone of both samples show absorption bands caused by spin-allowed d-d transitions in [6]-coordinated Fe2+, and no intervalence charge transfer Fe2+-Ti interactions, indicating that Fe2+ is the only chromophore. Mössbauer analysis of the blue zone of the Fucili sample confirmed the Fe2+ oxidation state, implying that the redox conditions in the crystallisation environment were relatively reducing. The presence of colour changes at the analogous termination during tourmaline crystal growth suggests a change in the composition of the crystallisation environment, probably associated with a partial opening of the system.
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| 4. |
- Altieri, Alessandra, et al.
(författare)
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Dark-coloured Mn-rich overgrowths in an elbaitic tourmaline crystal from the Rosina pegmatite, San Piero in Campo, Elba Island, Italy: witness of late-stage opening of the geochemical system
- 2023
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 87:1, s. 130-142
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Tidskriftsartikel (refereegranskat)abstract
- Multicoloured tourmalines from Elba Island, commonly display dark-coloured terminations due to incorporation of Fe, and also occasionally Mn. The mechanisms which led to the availability of these elements in the late-stage residual fluids are not yet completely understood. For this purpose, we investigated a representative tourmaline crystal found naturally in two fragments within a wide miarolitic cavity in the Rosina pegmatite (San Piero in Campo, Elba Island, Italy), and characterised by late-stage dark-coloured overgrowths. Microstructural and paragenetic observations, together with compositional and spectroscopic data (electron microprobe and optical absorption spectroscopy), provide evidence which shows that the formation of the dark-coloured Mn-rich overgrowths are the result of a pocket rupture. This event caused alteration of the cavity-coating spessartine garnet by highly-reactive late-stage cavity fluids by leaching processes, with the subsequent release of Mn to the residual fluids. We argue that the two fragments were originally a single crystal, which underwent natural breakage followed by the simultaneous growth of Mn-rich dark terminations at both breakage surfaces. This conclusion supports the evidence for a pocket rupture event, responsible for both the shattering of the tourmaline crystal and the compositional variation of the cavity-fluids related to the availability of Mn, which was incorporated by the tourmaline crystals. Additionally, a comparison of the dark overgrowths formed at the analogous and the antilogous poles, provides information on tourmaline crystallisation at the two different poles. The antilogous pole is characterised by a higher affinity for Ca, F and Ti, and a selective uptake of Mn2+, even in the presence of a considerable amount of Mn3+ in the system. This uneven uptake of Mn ions resulted in the yellow–orange colouration of the antilogous overgrowth (Mn2+ dependent) rather than the purple-reddish colour of the analogous overgrowths (Mn3+ dependent).
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| 5. |
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| 6. |
- Berg, Sylvia, 1986-, et al.
(författare)
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Exceptionally high whole-rock delta O-18 values in intra-caldera rhyolites from Northeast Iceland
- 2018
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Ingår i: Mineralogical magazine. - : MINERALOGICAL SOC. - 0026-461X .- 1471-8022. ; 82:5, s. 1147-1168
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Tidskriftsartikel (refereegranskat)abstract
- The Icelandic crust is characterized by low delta O-18 values that originate from pervasive high-temperature hydrothermal alteration by O-18-depleted meteoric waters. Igneous rocks in Iceland with delta O-18 values significantly higher than unaltered oceanic crust (similar to 5.7 parts per thousand) are therefore rare. Here we report on rhyolitic intra-caldera samples from a cluster of Neogene central volcanoes in Borgarfjorour Eystri, Northeast Iceland, that show whole-rock delta O-18 values between +2.9 and +17.6 parts per thousand (n = 6), placing them among the highest delta O-18 values thus far recorded for Iceland. Extra-caldera rhyolite samples from the region, in turn, show delta O-18 whole-rock values between +3.7 and +7.8 parts per thousand (n = 6), consistent with the range of previously reported Icelandic rhyolites. Feldspar in the intra-caldera samples (n = 4) show delta O-18 values between +4.9 and +18.7 parts per thousand, whereas pyroxene (n = 4) shows overall low delta O-18 values of +4.0 to +4.2 parts per thousand, consistent with regional rhyolite values. In combination with the evidence from mineralogy and rock H2O contents, the high whole-rock delta O-18 values of the intra-caldera rhyolites appear to be the result of pervasive isotopic exchange during subsolidus hydrothermal alteration with O-18-enriched water. This alteration conceivably occurred in a near-surface hot spring environment at the distal end of an intra-caldera hydrothermal system. and was probably fed by waters that had already undergone significant isotope exchange with the country rock. Alternatively, O-18-enriched alteration fluids may have been produced during evaporation and boiling of standing water in former caldera lakes, which then interacted with the intra-caldera rock suites. Irrespective of the exact exchange processes involved, a previously unrecognized and highly localized delta O-18-enriched rock composition exists on Iceland and thus probably within the Icelandic crust too.
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| 7. |
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| 8. |
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| 9. |
- Biagioni, Cristian, et al.
(författare)
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Bianchiniite, Ba2(Ti4+V3+)(As2O5)2OF, a new diarsenite mineral fromthe Monte Arsiccio mine, Apuan Alps, Tuscany, Italy
- 2021
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 3, s. 354-363
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Tidskriftsartikel (refereegranskat)abstract
- The new mineral bianchiniite, Ba2(Ti4+V3+)(As2O5)2OF, has been discovered in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. It occurs as brown {001} tabular crystals, up to 1 mm across, with a vitreous lustre. It is brittle, with a perfect {001} cleavage. Streak is brownish. In reflected light, bianchiniite is grey, with orange–yellow internal reflections. It is weakly bireflectant, with a very weak anisotropy in shades of grey. Minimum and maximum reflectance data for COM wavelengths [Rmin/Rmax (%), (λ, nm)] are: 5.0/5.8 (470),5.7/6.5 (546), 5.7/7.0 (589) and 5.2/6.3 (650). Electron microprobe analyses gave (wt.% – average of 10 spot analyses): TiO2 10.34, V2O33.77, Fe2O3 3.76,As2O3 44.36, Sb2O3 0.22, SrO 0.45, BaO 34.79, PbO 0.28, F 1.77, sum 99.74, –O=F–0.75, total 98.99. On the basis of 12 anions per formula unit, the empirical formula of bianchiniite is (Ba2.00Sr0.04Pb0.02)Σ2.06(Ti4+1.14V3+0.44Fe3+0.42)Σ2.00[(As3.96Sb0.02)Σ3.98O10](O1.18F0.82)Σ2.00. Bianchiniite is tetragonal, space group I4/mcm, with unit-cell parameters a = 8.7266(4), c = 15.6777(7) Å, V = 1193.91(12) Å3 and Z = 8. Its crystal structure was refined from single-crystal X-ray diffraction data to R1 = 0.0134 on the basis of 555 unique reflections with Fo > 4σ(Fo)and 34 refined parameters. The crystal structure shows columns of corner-sharing [Ti/(V,Fe)]-centred octahedra running along c, connected along a and b through (As2O5) dimers. A {001} layer of Ba-centred [10+2]-coordinated polyhedra is intercalated between (As2O5) dimers. Bianchiniite has structural relations with fresnoite- and melilite-group minerals. The name honours the two mineral collectors Andrea Bianchini (b. 1959) and Mario Bianchini (b. 1962) for their contribution to the knowledge of the mineralogy of pyrite ± baryte ± iron-oxide ore deposits from the Apuan Alps.
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| 10. |
- Biagioni, Cristian, et al.
(författare)
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Derbylite and graeserite from the Monte Arsiccio mine, Apuan Alps,Tuscany, Italy: occurrence and crystal-chemistry
- 2020
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 84:5, s. 766-777
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Tidskriftsartikel (refereegranskat)abstract
- New occurrences of derbylite, Fex2+Fe3+4–2xTi4+3+xSb3+O13(OH), and graeserite, Fex2+Fe3+4–2xTi4+3+xAs3+O13(OH), have been identified in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. Derbylite occurs as prismatic to acicular black crystals in carbonate veins. Iron and Ti are replaced by V (up to 0.29 atoms per formula unit, apfu) and minor Cr (up to 0.04 apfu). Mössbauer spectroscopy confirmed the occurrence of Fe2+ (up to 0.73 apfu), along with Fe3+. The Sb/(As+Sb) atomic ratio ranges between 0.73 and 0.82. Minor Ba and Pb (up to 0.04 apfu) substitute. Derbylite is monoclinic, space group P21/m, with unit-cell parameters a = 7.1690(3), b = 14.3515(7),c = 4.9867(2) Å, β = 104.820(3)° and V = 495.99(4) Å3. The crystal structure was refined to R1 = 0.0352 for 1955 reflections with Fo > 4σ(Fo). Graeserite occurs as prismatic to tabular black crystals, usually twinned, in carbonate veins or as porphyroblasts in schist. Graeserite in the first kind of assemblage is V rich (up to 0.66 apfu), and V poor in the second kind (0.03 apfu). Along with minor Cr (up to 0.06 apfu), this element replaces Fe and Ti. The occurrence of Fe2+ (up to 0.68 apfu) is confirmed by Mössbauer spectroscopy. Arsenic is dominant over Sb and detectable amounts of Ba and Pb have been measured (up to 0.27 apfu). Graeserite is monoclinic, space group C2/m, with unit-cell parameters for two samples: a = 5.0225(7), b = 14.3114(18), c = 7.1743(9) Å,β = 104.878(3)°, V = 498.39(11) Å3; and a = 5.0275(4), b = 14.2668(11), c = 7.1663(5) Å, β = 105.123(4)° and V = 496.21(7) Å3. The crystal structures were refined to R1 = 0.0399 and 0.0237 for 428 and 1081 reflections with Fo > 4σ(Fo), respectively. Derbylite and graeserite are homeotypic. They share the same tunnel structure, characterised by an octahedral framework and cuboctahedral cavities, hosting (As/Sb)O3 groups and (Ba/Pb) atoms.
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| 11. |
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| 12. |
- Bosi, Ferdinando, et al.
(författare)
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Crystal-chemical aspects of the roméite group, A2Sb2O6Y, of the pyrochlore supergroup
- 2017
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 81:6, s. 1287-1302
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Tidskriftsartikel (refereegranskat)abstract
- Four specimens of the roméite-group minerals oxyplumboroméite and fluorcalcioroméite from the Långban Mn-Fe deposit in Central Sweden were structurally and chemically characterized by single-crystal X-ray diffraction, electron microprobe analysis and infrared spectroscopy. The data obtained and those on additional roméite samples from literature show that the main structural variations within the roméite group are related to variations in the content of Pb2+, which is incorporated into the roméite structure via the substitution Pb2+ → A2+ where A2+ = Ca, Mn and Sr. Additionally, the cation occupancy at the six-fold coordinated B site, which is associated with the heterovalent substitution BFe3+ + Y□ → BSb5+ + YO2–, can strongly affect structural parameters.Chemical formulae of the roméite minerals group are discussed. According to crystal-chemical information, the species associated with the name ‘kenoplumboroméite’, hydroxycalcioroméite and fluorcalcioroméite most closely approximate end-member compositions Pb2(SbFe3+)O6□, Ca2(Sb5+Ti)O6(OH) and (CaNa)Sb2O6F, respectively. However, in accord with pyrochlore nomenclature rules, their names correspond to multiple end-members and are best described by the general formulae: (Pb,#)2(Sb,#)2O6□, (Ca,#)2(Sb,#)2O6(OH) and (Ca,#)Sb2(O,#)6F, where ‘#’ indicates an unspecified charge-balancing chemical substituent, including vacancies.
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| 13. |
- Bosi, Ferdinando, et al.
(författare)
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Experimental evidence for partial Fe2+ disorder at the Y and Z sites of tourmaline: a combined EMP, SREF, MS, IR and OAS study of schorl
- 2015
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 79:3, s. 515-528
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study of an Al-rich schorl sample from Cruzeiro mine (Minas Gerais, Brazil) was carried out using electron microprobe analysis, structural refinement and Mössbauer, infrared and optical absorption spectroscopy in order to explore the disordering of Fe2+ over the Y and Z sites of the tourmaline structure.A structural formula was obtained by merging chemical and structural data. The cation distribution at the two non-equivalent octahedrally coordinated sites (Y and Z) was obtained by two different optimization procedures which, minimizing the residuals between observed and calculated data, converged to the formula: X(Na0.65〈0.32Ca0.02K0.01)Σ1.00Y(Fe1.652+Al1.15Fe0.063+Mn0.052+Zn0.05Ti0.044+)Σ3.00Z(Al5.52Fe0.302+Mg0.18)Σ6.00[T(Si5.87Al0.13)Σ6.00O18](BBO3)3V(OH)3W[(OH)0.34F0.28O0.38]Σ1.00.This result shows a partial disordering of Fe2+ over the Y and Z sites which explains adequately the mean atomic number observed for the Z site (13.5±0.1). Such a disordering is also in line with the shoulder recorded in the Mössbauer spectrum (fitted by a doublet with isomer shift of 1.00 mm/s and quadrupole splitting of 1.38 mm/s) as well as with the asymmetric bands recorded in the optical absorption spectrum at ∼9000 and 14,500 cm–1 (modelled by four Gaussian bands, centred at 7677 and 9418 cm–1, and 13,154 and 14,994 cm–1, respectively).The high degree of consistency in the results obtained using the different methods suggests that the controversy over Fe2+ order can be ascribed to the failure to detect small amounts of Fe2+ at Z (typically <<10% atoms/site) rather than a steric effect of Fe2+ on the tourmaline structure.
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| 14. |
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| 15. |
- Bosi, Ferdinando, et al.
(författare)
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Mn-bearing purplish-red tourmaline from the Anjanabonoina pegmatite, Madagascar
- 2021
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 85:2, s. 242-253
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Tidskriftsartikel (refereegranskat)abstract
- A gem-quality purplish-red tourmaline sample of alleged liddicoatitic composition from the Anjanabonoina pegmatite, Madagascar, hasbeen fully characterised using a multi-analytical approach to define its crystal-chemical identity. Single-crystal X-ray diffraction, chem-ical and spectroscopic analysis resulted in the formula: X(Na0.41□0.35Ca0.24)Σ1.00Y(Al1.81Li1.00Fe3+0.04Mn3+0.02Mn2+0.12Ti0.004)Σ3.00ZAl6[T(Si5.60B0.40)Σ6.00O18](BO3)3(OH)3W[(OH)0.50F0.13O0.37]Σ1.00, which corresponds to the tourmaline species elbaite having the typical space group R3m and relatively small unit-cell dimensions, a= 15.7935(4) Å, c= 7.0860(2) Å and V= 7.0860(2) Å3.Optical absorption spectroscopy showed that the purplish-red colour is caused by minor amounts of Mn3+(Mn2O3= 0.20 wt.%).Thermal treatment in air up to 750°C strongly intensified the colour of the sample due to the oxidation of all Mn2+ to Mn3+ (Mn2O3 up to 1.21 wt.%). Based on infrared and Raman data, a crystal-chemical model regarding the electrostatic interaction betweenthe X cation and W anion, and involving the Y cations as well, is proposed to explain the absence or rarity of the mineral species ‘liddicoatite’.
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| 16. |
- Bosi, Ferdinando, et al.
(författare)
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On the application of the IMA-CNMNC dominant-valency rule to complex mineral compositions
- 2019
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 83:5, s. 627-632
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Tidskriftsartikel (refereegranskat)abstract
- Mineral species should be identified by an end-member formula and by using the dominant-valency rule as recommended by the IMA–CNMNC. However, the dominant-end-member approach has also been used in the literature. These two approaches generally converge, but for some intermediate compositions, significant differences between the dominant-valency rule and the dominant end-member approach can be observed. As demonstrated for garnet-supergroup minerals, for example, the end-member approach is ambiguous, as end-member proportions strongly depend on the calculation sequence. For this reason, the IMA–CNMNC strongly recommends the use of the dominant-valency rule for mineral nomenclature, because it alone may lead to unambiguous mineral identification. Although the simple application of the dominant-valency rule is successful for the identification of many mineral compositions, sometimes it leads to unbalanced end-member formulae, due to the occurrence of a coupled heterovalent substitution at two sites along with a heterovalent substitution at a single site. In these cases, it may be useful to use the site-total-charge approach to identify the dominant root-charge arrangement on which to apply the dominant-constituent rule. The dominant-valency rule and the site-totalcharge approach may be considered two procedures complementary to each other for mineral identification. Their critical point is to find the most appropriate root-charge and atomic arrangements consistent with the overriding condition dictated by the end-member formula. These procedures were approved by the IMA−CNMNC in May 2019.
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| 17. |
- Bosi, Ferdinando, et al.
(författare)
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Princivalleite, Na(Mn2Al)Al6(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup from Veddasca Valley, Varese, Italy
- 2022
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 86:1, s. 78-86
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Tidskriftsartikel (refereegranskat)abstract
- Princivalleite, Na(Mn2Al)Al6(Si6O18)(BO3)3(OH)3O, is a new mineral (IMA2020-056) of the tourmaline supergroup. It occurs in the Veddasca Valley, Luino area, Varese, Lombardy, Italy (46°03’30.74’’N, 8°48’24.47’’E) at the centre of a narrow (2–3 cm wide) vertical pegmatitic vein, a few metres long, crosscutting a lens of flaser gneiss. Crystals are subhedral (up to 10 mm in size), azure with a vitreous lustre, conchoidal fracture and white streak. Princivalleite has a Mohs hardness of ~7, a calculated density of 3.168 g/cm3 and is uniaxial (–). Princivalleite has trigonal symmetry, space group R3m, a = 15.9155(2) Å, c = 7.11660(10) Å, V = 1561.15(4) Å3 and Z = 3. The crystal structure was refined to R1 = 1.36% using 1758 unique reflections collected with MoKα X-ray intensity data. Crystal-chemical analysis resulted in the empirical crystal-chemical formulaX(Na0.54Ca0.11□0.35)Σ1.00Y(Al1.82Mn2+0.84Fe2+0.19Zn0.07Li0.08)Σ3.00Z(Al5.85Fe2+0.13Mg0.02)Σ6.00[T(Si5.60Al0.40)Σ6.00O18](BO3)3O(3)[(OH)2.71O0.29]Σ3.00O(1)[O0.66F0.22(OH)0.12]Σ1.00 which recast in its ordered form for classification purposes is:X(Na0.54Ca0.11□0.35)Σ1.00Y(Al1.67Mn2+0.84Fe2+0.32Zn0.07Mg0.02Li0.08)Σ3.00ZAl6.00[T(Si5.60Al0.40)Σ6.00O18](BO3)3V[(OH)2.71O0.29]Σ3.00W[O0.66F0.22(OH)0.12]Σ1.00.Princivalleite is an oxy-species belonging to the alkali group of the tourmaline supergroup. The closest end-member compositions of valid tourmaline species are those of oxy-schorl and darrellhenryite, to which princivalleite is related by the substitutions Mn2+ ↔ Fe2+ and Mn2+ ↔ 0.5Al3+ + 0.5Li+, respectively. Princivalleite from Veddasca Valley is a geochemical anomaly, originated in a B-rich and peraluminous anatectic pegmatitic melt formed in situ, poor in Fe and characterised by reducing conditions in the late-stage metamorphic fluids derived by the flaser gneiss. The Mn-enrichment in this new tourmaline is due to absence of other minerals competing for Mn such as garnet.
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| 18. |
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| 19. |
- Broman, Curt, et al.
(författare)
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Deposition conditions for the indium-bearing polymetallic quartz veins at Sarvlaxviken, south-eastern Finland
- 2018
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 82, s. S43-S59
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Tidskriftsartikel (refereegranskat)abstract
- Polymetallic quartz veins, with up to 1500ppm indium, have been discovered recently in the Sarvlaxviken area within the 1.64Ga anorogenic multiphase Wiborg rapakivi batholith and adjacent 1.90Ga Svecofennian crust in SE Finland. Evidence from primary fluid inclusions in the Sarvlaxviken area provides new information on the hydrothermal transport and depositional processes of metals in anorogenic granites. Fluid inclusions with variable aqueous liquid and vapour proportions (5-90vol.% vapour) occur in quartz, cassiterite and fluorite belonging to three generations of polymetallic quartz veins. Microthermometry indicates that the veins were deposited at temperatures that range from similar to 500 degrees C down to <100 degrees C and salinities from 0 to 16 eq. mass% NaCl. Fluid inclusion data show that the depositional conditions were similar regardless of vein generation. The interpreted depositional processes involve phase separation with a combination of condensation, cooling and boiling of an initially low-salinity (<3 eq. mass% NaCl) aqueous magmatic vapour phase enriched in CO2-F-Cl-S and metals. Fluid inclusions with low salinities dominate, but higher salinities are recorded in metal-rich parts of the veins. The turbulent fluid flow, with complex geometry and temperature-salinity patterns, may explain why sulfide and/or oxide opaque minerals occur irregularly, and are locally the dominating vein minerals, but disappear completely into barren parts of the quartz veins. All fluids are considered to have been generated by the F-rich Marviken granite (and related granite dykes), which show all geochemical criteria for an ore-fertile granite. The quartz veins investigated in the adjacent Svecofennian country rocks are considered to represent the very last stage of a fluid with similar characteristics to the fluid responsible for the ore formation in the Sarvlaxviken area, but that had cooled to <100 degrees C.
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| 20. |
- Cabri, Louis J., et al.
(författare)
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A review of hexaferrum based on new mineralogical data
- 2018
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Ingår i: Mineralogical magazine. - : Mineralogical Society of Great Britain and Ireland. - 0026-461X .- 1471-8022. ; 82:3, s. 531-538
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Tidskriftsartikel (refereegranskat)abstract
- Hexaferrum, defined as an hcp Fe mineral containing varying amounts of Ru, Os, or Ir(Mochalov et al. 1998) was re-examined in the light of new analyses of similar alloys from the Loma Peguera and Loma Larga chromitites, in the central part of Loma Caribe peridotite, Cordillera Central of the Dominican Republic, together with a review of the phase chemistry inthe Fe-Ni-Ir and Fe-Ru-Ir systems. We conclude that the hcp (Fe,Ir) mineral corresponds to theε-phase of Raub et al. (1964) and should be differentiated from hexaferrum [(Fe,Os) and(Fe,Ru)] because it is separated by one to two miscibility gaps and therefore is not a continuous solid solution with Fe.
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| 21. |
- Cámara, Fernando, et al.
(författare)
-
As-bearing new mineral species from Valletta mine, Maira Valley, Piedmont, Italy: IV. Lombardoite, Ba2Mn3+(AsO4)2(OH) and aldomarinoite, Sr2Mn3+(AsO4)2(OH), description and crystal structure
- 2022
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 86:3, s. 447-458
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Tidskriftsartikel (refereegranskat)abstract
- Lombardoite, ideally Ba2Mn3+(AsO4)2(OH), and aldomarinoite, ideally Sr2Mn3+(AsO4)2(OH), are two new minerals of the arsenbrackebuschite group in the brackebuschite supergroup, discovered in Fe–Mn ore in metaquartzites of the abandoned mine of Valletta, Canosio, Val Maira, Cuneo Province, Piedmont, Italy. They occur as red–brown and orange brown, respectively, as subhedral crystals (< 0.5 mm) in thin masses, associated with quartz, aegirine, baryte, calcite, hematite, muscovite and Mn minerals such as cryptomelane, braunite and manganberzeliite. Both minerals are translucent, have yellow–orange streak and vitreous lustre. Both are brittle. Estimated Mohs hardness is 6–6½ for lombardoite (by analogy to canosioite), and 4½–5 for aldomarinoite (by analogy to tokyoite). Calculated densities are 5.124 g/cm3 for lombardoite and 4.679 g/cm3 for aldomarinoite. Both minerals are biaxial (+). Lombardoite shows 2Vz(meas.) = 78(4)° and is pleochroic with X = yellowish brown, Y = brown and Z = reddish brown (Z > Y > X). Aldomarinoite has 2Vz(meas.) = 67.1(1)°, and is pleochroic with X = brown, Y = brownish orange and Z = yellowish brown (Z > Y > X). Point analyses by electron microprobe using wavelength dispersive spectroscopy resulted in the empirical formula (based on 9 O anions): (Ba1.96Sr0.17Pb0.04Na0.02Ca0.02)Σ2.21(Mn3+0.62Fe3+0.13Al0.06Mg0.11)Σ0.92[(As0.87V0.12P0.01)Σ1.00O4]2(OH) for lombardoite, and (Sr1.93Ca0.21Ba0.04Pb0.01)Σ2.19(Mn3+0.48Al0.35Fe3+0.21Mg0.01)Σ1.05[(As0.92V0.03)Σ0.95O4]2(OH) for aldomarinoite. The absence of H2O was confirmed by Raman spectroscopy and infrared spectroscopy. Both minerals are monoclinic, P21/m, with unit-cell parameters a = 7.8636(1) Å, b = 6.13418(1) Å, c = 9.1197(1) Å, β = 112.660(2)° and V = 405.94(1) Å3, for lombardoite and a = 7.5577(4) Å, b = 5.9978(3) Å, c = 8.7387(4) Å, β = 111.938(6)° and V = 367.43(3) Å3, for aldomarinoite. The eight strongest powder X-ray diffraction lines are [d, Å (Irel) (hkl)]: 6.985 (39) (10$\bar{1}$), 3.727 (33) (111), 3.314 (100) (21$\bar{1}$), 3.073 (24) (020), 3.036 (33) (21$\bar{2}$, 10$\bar{3}$), 2.810 (87) (12$\bar{1}$, 112), 2.125 (20) (301, 11$\bar{4}$) and 1.748 (24) (321) for lombardoite and 3.191 (89) (21$\bar{1}$), 2.997 (45) (020), 2.914 (47) (21$\bar{2}$, 10$\bar{3}$), 2.715 (100) (112), 2.087 (39) (12$\bar{3}$, 1.833 (32) (31$\bar{4}$), 1.689 (36) (321), 1.664 (21) (132) for aldomarinoite. The minerals are isostructural with brackebuschite: infinite chains of edge sharing octahedra running parallel to the b axis and decorated with AsO4 groups are connected along the a and c axes through Ba and Sr atoms in lombardoite and aldomarinoite, respectively. The minerals are named after Bruno Lombardo (1944–2014), geologist and petrologist at C.N.R. (National Research Council of Italy), and Aldo Marino (b. 1942) the mineral collector and founding member of the AMI – Italian Micromineralogical Association.
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| 22. |
- Cámara, Fernando, et al.
(författare)
-
Piccoliite, NaCaMn3+2(AsO4)2O(OH), a new arsenate from the manganese deposits of Montaldo di Mondovì and Valletta, Piedmont, Italy
- 2023
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 87:2, s. 204-217
-
Tidskriftsartikel (refereegranskat)abstract
- Piccoliite, ideally NaCaMn3+2(AsO4)2O(OH), is a new mineral discovered in the Fe–Mn ore hosted in metaquartzites of the Montaldo di Mondovì mine, Corsaglia Valley, Cuneo Province, Piedmont, Italy. It occurs as small and rare black crystals and aggregates hosted by a matrix of quartz, associated with calcite and berzeliite/manganberzeliite. It has been also found in the Valletta mine near Canosio, Maira Valley, Cuneo Province, Piedmont, Italy, where it occurs embedded in quartz associated with grandaite, hematite, tilasite/adelite and rarely thorianite. The mineral is opaque (thin splinters may be very dark red), with brown streak and has a resinous to vitreous lustre. It is brittle with irregular fracture. No cleavage has been observed. The measured Mohs hardness is ~5–5.5. Piccoliite is non fluorescent. The calculated density is 4.08 g⋅cm–3. Chemical spot analyses by electron microprobe analysis using wavelength dispersive spectroscopy resulted in the empirical formula (based on 10 anions per formula unit) (Na0.64Ca0.35)Σ0.99(Ca0.75Na0.24)Σ0.99(Mn3+1.08Fe3+0.59Mg0.20Ca0.10)Σ1.97(As2.03V0.03Si0.01)Σ2.07O9(OH) and (Na0.53Ca0.47)Σ1.00(Ca0.76Na0.23Sr0.01)Σ1.00(Mn3+0.63Fe3+0.49Mg0.48Mn4+0.34Ca0.06)Σ2.00(As1.97P0.01Si0.01)Σ1.99O9(OH) for the Montaldo di Mondovì and Valletta samples, respectively. The mineral is orthorhombic, Pbcm, with single-crystal unit-cell parameters a = 8.8761(9), b = 7.5190(8), c = 11.689(1) Å and V = 780.1(1) Å3 (Montaldo di Mondovì sample) and a = 8.8889(2), b = 7.5269(1), c = 11.6795(2) Å, V = 781.43(2) Å3 (Valletta sample) with Z = 4. The seven strongest powder X-ray diffraction lines for the sample from Montaldo di Mondovì are [d Å (Irel; hkl)]: 4.85 (57; 102), 3.470 (59; 120, 113), 3.167 (100; 022), 2.742 (30; 310, 213), 2.683 (53; 311, 023), 2.580 (50; 222, 114) and 2.325 (19; 320, 214, 223). The crystal structure (R1 = 0.0250 for 1554 unique reflections for the Montaldo di Mondovì sample and 0.0260 for 3242 unique reflections for the Valletta sample) has MnO5(OH) octahedra forming edge-shared dimers; these dimers are connected through corner-sharing, forming two-up-two-down [[6]M2([4]TO4)4φ2] chains [M = Mn; T = As; φ = O(OH)] running along [001]. These chains are bonded in the a and b directions by sharing corners with AsO4 tetrahedra, giving rise to a framework of tetrahedra and octahedra hosting seven-coordinated Ca2+ and Na+ cations. The crystal structure of piccoliite is closely related to that of pilawite-(Y) as well as to carminite-group minerals that also show the same type of chains but with different linkage. The mineral is named after the mineral collectors Gian Paolo Piccoli and Gian Carlo Piccoli (father and son) (1926–1996 and b. 1953, respectively), the latter having discovered the type material at the Montaldo di Mondovì mine.
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| 23. |
- Clayton, R.E, et al.
(författare)
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Fe isotope fractionation during the precipitation of ferrihydrite and transformation of ferrihydrite to goethite
- 2005
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 69:5, s. 667-676
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Tidskriftsartikel (refereegranskat)abstract
- Ferrihydrite and goethite are amongst the most important substrates for the sorption of contaminants in soil and other environmental media. Isotopic studies of the transition elements, particularly those that exhibit more than one oxidation state and show pH- and/or redox-sensitive behaviour at low temperatures, have been shown to be potentially useful present-day and past proxies for redox (or palaeoredox) conditions. We have made preliminary investigations of Fe isotope fractionation that take place during the formation of FeIII (oxy)hydroxides (FeIIIox) from an aqueous FeIII(NO3)3 solution (FeIIIaq) under laboratory conditions. We have attempted to keep the chemical system simple by excluding 'vital effects' and major changes in redox through the maintenance of abiotic conditions and use of FeIIIaq. Isotopic measurements (56Fe/54Fe, 57Fe/54Fe) of the FeIII(NO3)3 stock solution, the original ferrihydrite and the mixed ferrihydrite/goethite-supernatant FeIIIaq 'pairs' were carried out using a double focusing multicollector inductively coupled plasma mass spectrometer. The results reveal an apparent systematic variation indicating larger ΔFeIIIaq-FeIIIox with decrease in the ferrihydrite:goethite ratio, which reflects the time allowed for isotopic exchange. These values range from virtually zero (0.03‰) after 24 h to 0.30‰ after 70 h. In each FeIIIox-FeIIIaq 'pair' the lighter Fe isotope is partitioned into the FeIIIox, leaving the FeIIIaq isotopically heavier. The observed fractionation reflects isotopic exchange of Fe between the FeIIIox and FeIIIaq upon at least a two step transition of ferrihydrite to goethite.
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| 24. |
- D'Ippolito, Veronica, et al.
(författare)
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Crystallographic and spectroscopic characterisation of a natural Zn-rich spinel approaching the endmember gahnite (ZnAl2O4) composition
- 2013
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 77, s. 2941-2953
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Tidskriftsartikel (refereegranskat)abstract
- The crystal chemistry of a natural, gem-quality, blue-grey Zn-rich spinel crystal from Jemaa, Kaduna State, Nigeria, was studied using electron microprobe, single-crystal X-ray diffraction, optical absorption and Raman spectroscopies. The composition of the crystal approaches the gahnite endmember (ZnAl2O4), ∼94 mol.%, with the remainder being dominated by a hercynite component (FeAl2O4). The unit-cell dimension is 8.0850(3) Å and the tetrahedral and octahedral bond distances are determined asT–O 1.9485(6) Å andM–O 1.9137(3) Å. Crystal chemical analysis resulted in the empirical structural formulaT(Zn0.94Fe2+0.03Al0.03)M(Al1.96Fe2+0.03Fe3+0.01)O4, which shows Zn and Al almost fully ordered in the tetrahedrally and octahedrally coordinatedTandMsites, respectively. Raman spectra obtained using the excitation of the blue 473.1 nm line of a Nd:YAG laser display three of the five Raman-active modes predicted for the general oxide spinel group of minerals. These are the Egmode at 420.6 cm–1and the T2gmodes at 510 cm–1and 661 cm–1, due to vibrations in the AlO6octahedra. Optical absorption spectra recorded in the UV/VIS-NIR-MIR range 2000 29000 cm–1show a dominant absorption band at ∼5000 cm–1which is caused by spin-allowed electronicd–dtransitions in Fe2+located at theTsites. The blue-grey hue exhibited by the sample is mainly due to spin-forbidden electronic transitions inTFe2+and toMFe2+↔MFe3+intervalence charge transfer, and the poor saturation of the colour is due to the small concentration of Fe2+and Fe3+.
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| 25. |
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| 26. |
- Emeleus, C. H., et al.
(författare)
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The Rum Igneous Centre, Scotland
- 2014
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 78:4, s. 805-839
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Tidskriftsartikel (refereegranskat)abstract
- The publication of the British Geological Survey memoir on Rum and the Small Isles in 1997 was followed by a period of intense petrological and mineralogical research, leading to some 40 papers, books and other publications. The research progress since then is reviewed here and integrated with the information previously available to provide an overview of the current status of understanding of the centre. New data on the acidic and mixed acid/basic magmas of the early Rum caldera demonstrate that frequent mafic replenishments were the main driver for magmatic activity at Rum right from its initial stages. The caldera is bound by the Main Ring Fault, a structure which probably also exercised an influence on the emplacement of the subsequent basic and ultrabasic intrusions. The later emplacement of gabbros and ultrabasic rocks caused only limited thermal metamorphism of the surrounding Torridonian sandstones, contrasting markedly with the crustal isotope signatures of the early intra-caldera ignimbrite magmas and the intense alteration of uplifted masses of Lewisian gneiss within the ring fault. Rare picritic dykes provide an indication of the possible parent magma for the mafic and ultrabasic rocks, but these, as with most other magmatic rocks on Rum, have undergone varying degrees of crustal contamination, involving both Lewisian granulite and amphibolite-type crust but, notably, no Moine metasedimentary compositions as is the case at the nearby Ardnamurchan centre. Detailed textural studies on the gabbroic and ultrabasic rocks allow a distinction between intrusive peridotites and peridotite that forms part of the classic layered cumulate units of Rum and, furthermore, this work and that on the chromite seams and veins in these rocks shows that movement of trapped magma and magma derived from later intrusions, may produce textures regarded previously as of primary cumulate origin. Sulfides in the chromitite seams and ultrabasic rocks, in turn, show possible influences from assimilated Mesozoic sediments. Igneous activity on Rum was short-lived, possibly only between 0.5 and 1 m.y. in duration and commenced at similar to 60.5 Ma. The Rum Central Complex was extinct by the time the main activity at the nearby Skye Central Complex commenced (similar to 59 Ma). From recent apatite fission-track studies it seems probable that Rum, in common with other Palaeogene centres, underwent a brief, but significantly later heating event (similar to 45 Ma).
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| 27. |
- Ferrow, Embaie
(författare)
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Fe-57 Mossbauer effect study of bannisterite: a modulated 2 : 1-type phyllosilicate
- 2006
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Ingår i: Mineralogical Magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 70:2, s. 187-199
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Tidskriftsartikel (refereegranskat)abstract
- Bannisterite is a modulated 2:1-type phyllosilicate having ten octahedral sites with hydroxyl groups in trans, cis and combined trans-cis configurations. Each octahedral site, depending on its proximity to the layer modulation, is exposed to a different degree of distortion. The electric field gradient at the Fe site and the site distortion are used to propose a model for the site assignment and oxidation mechanism in bannisterite. The results show that two models are compatible with the experimental results of fitting the spectrum of bannisterite. However, the model which allows for site distortion accounts better for the observed line overlap of the Fe-[6](2+) sites. Accordingly, the octahedral sites with a greater degree of distortion are assigned to the Fe-[6](2+) with lower electric quadrupole splitting, and the octahedral sites with lower site distortion are assigned to the Fe-[6](2+) with higher electric quadrupole splitting. Moreover, the ease of oxidation decreases in the order trans > trans-cis > cis.
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| 28. |
- Frank, Katherine S., et al.
(författare)
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Magnetite as a provenance and exploration tool to metamorphosed base-metal sulfide deposits in the Stollberg ore field, Bergslagen, Sweden
- 2022
-
Ingår i: Mineralogical magazine. - : Cambridge University Press. - 0026-461X .- 1471-8022. ; 86:3, s. 373-396
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Tidskriftsartikel (refereegranskat)abstract
- Magnetite is a common mineral in the Paleoproterozoic Stollberg Zn–Pb–Ag plus magnetite ore field (~6.6 Mt of production), which occurs in 1.9 Ga metamorphosed felsic and mafic rocks. Mineralisation at Stollberg consists of magnetite bodies and massive to semi-massive sphalerite–galena and pyrrhotite (with subordinate pyrite, chalcopyrite, arsenopyrite and magnetite) hosted by metavolcanic rocks and skarn. Magnetite occurs in sulfides, skarn, amphibolite and altered metamorphosed rhyolitic ash–siltstone that consists of garnet–biotite, quartz–garnet–pyroxene, gedrite–albite, and sericitic rocks. Magnetite probably formed from hydrothermal ore-bearing fluids (~250–400°C) that replaced limestone and rhyolitic ash–siltstone, and subsequently recrystallised during metamorphism. The composition of magnetite from these rock types was measured using electron microprobe analysis and LA–ICP–MS. Utilisation of discrimination plots (Ca+Al+Mn vs. Ti+V, Ni/(Cr+Mn) vs. Ti+V, and trace-element variation diagrams (median concentration of Mg, Al, Ti, V, Co, Mn, Zn and Ga) suggest that the composition of magnetite in sulfides from the Stollberg ore field more closely resembles that from skarns found elsewhere rather than previously published compositions of magnetite in metamorphosed volcanogenic massive sulfide deposits. Although the variation diagrams show that magnetite compositions from various rock types have similar patterns, principal component analyses and element–element variation diagrams indicate that its composition from the same rock type in different sulfide deposits can be distinguished. This suggests that bulk-rock composition also has a strong influence on magnetite composition. Principal component analyses also show that magnetite in sulfides has a distinctive compositional signature which allows it to be a prospective pathfinder mineral for sulfide deposits in the Stollberg ore field.
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| 29. |
- Gatta, Diego, et al.
(författare)
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H-bonding scheme in allactite: a combined single-crystal X-ray and neutron diffraction, optical absorption spectroscopy, FTIR and EPMA-WDS study
- 2016
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 80:5, s. 719-732
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Tidskriftsartikel (refereegranskat)abstract
- The crystal chemistry of allactite from Långban, Värmland (Sweden) was investigated by single-crystal X-ray and neutron diffraction, optical absorption spectroscopy, Fourier-transform infra-red spectroscopy (FTIR) and electron microprobe analysis by wavelength-dispersive spectroscopy (EPMA-WDS). The optical spectra indicate the presence of Mn in valence state 2+ only. Assuming 16 O atoms per formula unit, arsenic as As5+ and the (OH) content calculated by charge balance, the resulting formula based on the EPMA-WDS data is (Mn6.732+Ca0.13Mg0.12Zn0.02)Σ7.00(As5+)2.00O16H8, very close to the ideal composition Mn7(AsO4)2(OH)8. In the unpolarized FTIR spectrum of allactite, fundamental (OH)-stretching bands are observed at 3236, 3288, 3387, 3446, 3484, 3562 and 3570 cm–1, suggesting that a number of OH environments, with different hydrogen bond strengths, occur in the structure. The neutron structure refinement shows that four independent H sites occur in allactite with full site occupancy, all as members of hydroxyl groups. The complex hydrogen-bonding scheme in the allactite structure is now well defined, with at least nine hydrogen bonds energetically favourable with mono-, bi- and trifurcated configurations.
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| 30. |
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| 31. |
- Grawunder, A, et al.
(författare)
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Origin of REE patterns in AMD-impacted areas
- 2013
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Ingår i: Mineralogical magazine. - : Walter de Gruyter. - 0026-461X .- 1471-8022. ; 77, s. 1210-1210
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Tidskriftsartikel (refereegranskat)
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| 32. |
- Grew, Edward S., et al.
(författare)
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Recommended nomenclature for the sapphirine and surinamite groups (sapphirine supergroup)
- 2008
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 72, s. 839-876
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Tidskriftsartikel (refereegranskat)abstract
- Minerals isostructural with sapphirine-1A, sapphirine-2M, and surinamite are closely related chain silicates that pose nomenclature problems because of the large number of sites and potential constituents, including several (Be, B, As, Sb) that are rare or absent in other chain silicates. Our recommended nomenclature for the sapphirine group (formerly aenigmatite group) makes extensive use of precedent, but applies the rules to all known natural compositions, with flexibility to allow for yet undiscovered compositions such as those reported in synthetic materials. These minerals are part of a polysomatic series composed of pyroxene or pyroxene-like and spinel modules, and thus we recommend that the sapphirine supergroup should encompass the polysomatic series. The first level in the classification is based on polysome, i.e. each group within the supergroup corresponds to a single polysome. At the second level, the sapphirine group is divided into subgroups according to the occupancy of the two largestMsites, namely, sapphirine (Mg), aenigmatite (Na), and rhönite (Ca). Classification at the third level is based on the occupancy of the smallestMsite with most shared edges,M7, at which the dominant cation is most often Ti (aenigmatite, rhönite, makarochkinite), Fe3+(wilkinsonite, dorrite, høgtuvaite) or Al (sapphirine, khmaralite); much less common is Cr (krinovite) and Sb (welshite). At the fourth level, the two most polymerizedTsites are considered together, e.g. ordering of Be at these sites distinguishes høgtuvaite, makarochkinite and khmaralite. Classification at the fifth level is based on XMg= Mg/(Mg + Fe2+) at theMsites (excluding the two largest andMl). In principle, this criterion could be expanded to include other divalent cations at these sites, e.g. Mn. To date, most minerals have been found to be either Mg-dominant (XMg> 0.5), or Fe2+-dominant (XMg< 0.5), at theseMsites. However, XMgranges from 1.00 to 0.03 in material described as rhönite, i.e. there are two species present, one Mg-dominant, the other Fe2+-dominant. Three other potentially new species are a Mg-dominant analogue of wilkinsonite, rhönite in the Allende meteorite, which is distinguished from rhonite and dorrite in that Mg rather than Ti or Fe3+is dominant atMl, and an Al-dominant analogue of sapphirine, in which Al > Si at the two most polymerizedTsitesvs. Al < Si in sapphirine. Further splitting of the supergroup based on occupancies other than those specified above is not recommended.
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| 33. |
- Gustafsson, Jon Petter, 1964-, et al.
(författare)
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Chromium (III) and bismuth (III) complexation to organic matter : EXAFS Spectroscopy and equilibrium modeling
- 2013
-
Ingår i: Mineralogical magazine. - 0026-461X .- 1471-8022. ; 77:5, s. 1235-
-
Tidskriftsartikel (refereegranskat)abstract
- The complexation of chromium(III) and bismuth(III) to organic matter was investigated by batch equilibrations with Suwannee River Fulvic Acid (SRFA) and with mor layer material (Risbergshöjden Oe). In the SRFA systems, 3 mM chromium(III) solutions were equilibrated with 9 g L-1 SRFA and equilibrated at different pH values ranging from 2 to 6. Characterization of the reaction products was made at MAX-Lab, Lund, Sweden, using Cr K-edge EXAFS spectroscopy at 5 989 eV. The spectra were interpreted using both conventional data treatment using EXAFSPAK and with wavelet transform (WT) analysis. The results show that chromium(III) formed monomeric organic complexes with SRFA. There was no evidence of polymerization with the exception of the particulate phase at pH 6, which was attributed to a limited extent of Cr(OH)3 formation.The mor layer material was equilibrated with chromium(III) and bismuth(III) solutions as a function of pH, time and competing ions (iron(III), aluminium(III), copper(II)). Again CrK-edge and Bi L3-edge EXAFS spectroscopy was used, at 5 989 and 13 419 eV. The experiments showed a predominance of monomeric organic complexes for chromium(III). The sorption of chromium(III) was pH-dependent and to some extent found to be influenced by competition from aluminium(III) and copper(II). Chromium(III) complexation was found to be very slow at pH < 4, and equilibration times of three months or longer were required to reach equilibrium under these conditions. Concerning bismuth(III), complexation was quicker and found to be very strong, with more than 94 % bound at pH 1.2 at a high bismuth(III) loading. EXAFS spectroscopy showed that two complexes were involved, one monomeric and one di- or trimeric, with the latter being predominant at higher pH values, although it was present already at pH 1.2. In the organic bismuth(III) complexes, the bismuth(III) octahedron was found to be strongly distorted, which implies strong binding to organic acid functional groups. The complexation of bismuth(III) remained essentially unchanged even in the presence of a potent competitor such as iron(III).The results from the spectroscopic investigation and from the quantitative solution data were used to calibrate new and improved complexation models for the Stockholm Humic (SHM) and the NICA-Donnan models. In the case of the Stockholm Humic Model, both complexes as found by EXAFS spectroscopy were considered explicitly; this ensured the model to predict minimum competition effects in agreement with the laboratory results.
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| 34. |
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| 35. |
- Herbert, Roger B
(författare)
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Zinc immobilization by zerovalent Fe : surface chemistry and mineralogy and reaction products
- 2003
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 67:6, s. 1285-1298
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Tidskriftsartikel (refereegranskat)abstract
- In bioreactor systems for the treatment of metal-contaminated water, pretreatment with zerovalent Fe can be exploited for oxygen consumption and H-2 Production. In this study, a column experiment is used to investigate the changes in surface chemistry and solid phase products that result from the reaction of a Zn-sulphate-lactate solution with zerovalent Fe filings. The results of this study indicate that zerovalent Fe is very effective in immobilizing dissolved Zn with a porewater residence time of 1.3-3.1 days. A combination of X-ray diffractometry, X-ray photoelectron spectroscopy, and mineral equilibria calculations indicates that Zn precipitates as Zn(OH)(2) and zincite at PH 9-10. At PH approximate to 6, Zn primarily adsorbs to abundant ferric oxyhydroxides, although incorporation in green rust is also considered. During the course of the experiment, the surface mineralogy changes from magnetite-lepidocrocite-goethite to green rust-akaganeite-goethite. The results suggest that the zerovalent Fe surface becomes passivated by a surface film of ferric oxyhydroxides, green rust and organic material, so that the rate of electron transfer and proton consuming reactions (i.e. oxygen consumption, H-2 generation) declines, resulting in a decrease in solution PH.
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| 36. |
- Herbert, Roger, 1966-, et al.
(författare)
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Pilot-scale barrier system for removal of nitrate in mine drainage
- 2011
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Ingår i: Mineralogical magazine. - 0026-461X .- 1471-8022. ; 75, s. 1012-1012
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Undetonated ammonium nitrate is readily soluble in water and quickly enters into the mine water and process water at amine site. In order to investigate the application of nitrate removal by denitrification in the cold climate of northern Sweden, a pilot-scale barrier system was constructed of sheet metal in autumn 2009 at the Malmberget iron ore mine. The barrier (9m x 2m x 1.5m) appears as an open basin with three inner dividing walls, and is filled with a reactive mixture consisting of crushed rock, sawdust, and sewage sludge. Water flows through the barrier at ca. 0.45 m3/hour.The chemical analyses of water flowing into and out of thebarrier during 2010 indicate that the degree of nitrate removal generally lay in the range between 11 and 77% of influent nitrate concentrations. Stable isotope analyses of δ15N and δ18O in nitrate demonstrate an enrichment in 15N and 18O in nitrate as water flows through the barrier, supporting theconclusion that denitrification is responsible for nitrateremoval. Ammonium concentrations in the barrier effluents are initially high, but these high levels are subsequently flushed from the barrier. In order to increase the degree of nitrate removal by denitrification in the barrier, a reactive carbon source needs to be added to the influent waters; this will be tested during the 2011 field season.
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| 37. |
- Hillier, Stephen
(författare)
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Determination of zeolite-group mineral compositions by electron probe microanalysis
- 2016
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Ingår i: Mineralogical Magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 80, s. 781-807
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Tidskriftsartikel (refereegranskat)abstract
- A new protocol for the quantitative determination of zeolite-group mineral compositions by electron probe microanalysis (wavelength-dispersive spectrometry) under ambient conditions, is presented. The method overcomes the most serious challenges for this mineral group, including new confidence in the fundamentally important Si-Al ratio. Development tests were undertaken on a set of natural zeolite candidate reference samples, representing the compositional extremes of Na, K, Cs, Mg, Ca, Sr and Ba zeolites, to demonstrate and assess the extent of beam interaction effects on each oxide component for each mineral. These tests highlight the variability and impact of component mobility due to beam interaction, and show that it can be minimized with recommended operating conditions of 15 kV, 2 nA, a defocused, 20 mu m spot size, and element prioritizing with the spectrometer configuration. The protocol represents a pragmatic solution that works, but provides scope for additional optimization where required. Vital to the determination of high-quality results is the attention to careful preparations and the employment of strict criteria for data reduction and quality control, including the monitoring and removal of non-zeolitic contaminants from the data (mainly Fe and clay phases). Essential quality criteria include the zeolite-specific parameters of R value (Si/(Si + Al + Fe3+), the 'E%' charge-balance calculation, and the weight percent of non-hydrous total oxides. When these criteria are applied in conjunction with the recommended analytical operating conditions, excellent inter-batch reproducibility is demonstrated. Application of the method to zeolites with complex solid-solution compositions is effective, enabling more precise geochemical discrimination for occurrence-composition studies. Phase validation for the reference set was conducted satisfactorily with the use ofX-ray diffraction and laser-ablation inductively-coupled plasma mass spectroscopy.
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| 38. |
- Hillier, Stephen
(författare)
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Linking derived debitage to the Stonehenge Altar Stone using portable X-ray fluorescence analysis
- 2022
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Ingår i: Mineralogical Magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 86
-
Tidskriftsartikel (refereegranskat)abstract
- The Altar Stone at Stonehenge in Wiltshire, UK, is enigmatic in that it differs markedly from the other bluestones. It is a grey-green, micaceous sandstone and has been considered to be derived from the Old Red Sandstone sequences of South Wales. Previous studies, however, have been based on presumed derived fragments (debitage) that have been identified visually as coming from the Altar Stone. Portable X-ray fluorescence (pXRF) analyses were conducted on these fragments (ex situ) as well as on the Altar Stone (in situ). Light elements (Z<37) in the Altar Stone analyses, performed after a night of heavy rain, were affected by surface and pore water that attenuate low energy X-rays, however the dry analyses of debitage fragments produced data for a full suite of elements. High Z elements, including Zr, Nb, Sr, Pb, Th and U, all occupy the same compositional space in the Altar Stone and debitage fragments, and are statistically indistinguishable, indicating the fragments are derived from the Altar Stone. Barium compares very closely between the debitage and Altar Stone, with differences being related to variable baryte distribution in the Altar Stone, limited accessibility of its surface for analysis, and probably to surface weathering. A notable feature of the Altar Stone sandstone is the presence of baryte (up to 0.8 modal%), manifest as relatively high Ba in both the debitage and the Altar Stone. These high Ba contents are in marked contrast with those in a small set of Old Red Sandstone field samples, analysed alongside the Altar Stone and debitage fragments, raising the possibility that the Altar Stone may not have been sourced from the Old Red Sandstone sequences of Wales. This high Ba 'fingerprint', related to the presence of baryte, may provide a rapid test using pXRF in the search for the source of the Stonehenge Altar Stone.
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| 39. |
- Hillier, Stephen
(författare)
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The Weaklaw Vent, SE Scotland: Metasomatism of eruptive products by carbo-hydro-fluids of probable mantle origin
- 2019
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Ingår i: Mineralogical Magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 83, s. 855-867
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Tidskriftsartikel (refereegranskat)abstract
- The Weaklaw vent in SE Scotland (East Lothian coast), inferred to be Namurian, produced lava spatter and volcanic bombs. The latter commonly contained ultramafic xenoliths. All were metasomatised by carbonic fluids rich in incompatible elements. The lavas and xenoliths are inferred to have been basanites and lherzolites prior to metasomatism. The abundance and size of (carbonated) peridotite xenoliths at Weaklaw denotes unusual rapidity of magma ascent and high-energy eruption making Weaklaw exceptional in the British Isles. The lavas and xenoliths were altered subsequently by low-temperature (<200 degrees C) carbo-hydrous fluids to carbonate, clay and quartz assemblages. A small irregular tuffisite 'dyke' that transects the ejecta is also composed dominantly of carbonates and clays. The peridotitic xenoliths are typically foliated, interpreted as originating as pre-entrainment mantle shear-planes.Analyses of the relic spinels shows them to be compositionally similar to spinets in local unaltered lherzolites from near-by basanitic occurrences. Chromium showed neither significant loss nor gain but was concentrated in a di-octahedral smectite allied to volkonskoite. It is in the complex association of smectite with other clays, chlorite and possibly fuchsite that the diverse incompatible elements are concentrated.We conclude that late Palaeozoic trans-tensional fault movement caused mantle shearing. Rapid ascent of basanite magma entrained large quantities of sheared lithospheric mantle. This was followed by ascent of an aggressive carbonate-/ hydroxyl-rich fluid causing pervasive metasomatism. The vent is unique in several ways: in its remarkable clay mineralogy and in displaying such high Cr-clays in a continental intra-plate setting; in being more productive in terms of its 'cargo' of peridotite xenoliths; in presenting an essentially un-eroded sequence of Namurian extrusives; and, not least, for giving evidence for post-eruptive, surface release of small-melt, deep-source fluids.
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| 40. |
- Holtstam, Dan, 1963-, et al.
(författare)
-
Crystal structure and composition of hiärneite, Ca2Zr4Mn3+SbTiO16, and constitution of the calzirtite group
- 2022
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 86:2, s. 314-318
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of hiärneite has been refined from single-crystal X-ray diffraction data (λ = 0.71073 Å) on type material from Långban, Värmland, Sweden. The refinement converged to R1 = 0.046 based on 1073 reflections with F2 > 4σ(F2). The tetragonal unit cell, space group I41/acd, has the parameters a = 15.2344(6) Å and c = 10.0891(6) Å with Z = 8. The mineral is isostructural with calzirtite, ideally Ca2Zr5Ti2O16, with a structural topology derived from fluorite. In hiärneite, Mn3+ is ordered at a 4- to 8-fold coordinated site (with a distorted polyhedral coordination figure), without the atom splitting encountered at the corresponding Zr-dominated site of calzirtite. The end-member formula for hiärneite is established as Ca2Zr4Mn3+SbTiO16. The calzirtite group, with calzirtite, hiärneite and tazheranite (cubic ZrO2-x), has been approved by the IMA–CNMNC.
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| 41. |
- Holtstam, Dan, 1963-, et al.
(författare)
-
Fluorbritholite-(Nd), Ca2Nd3(SiO4)3F, a new and key mineral for neodymium sequestration in REE skarns
- 2023
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Ingår i: Mineralogical magazine. - 0026-461X .- 1471-8022. ; 87:5, s. 731-737
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Tidskriftsartikel (refereegranskat)abstract
- Fluorbritholite-(Nd), ideally Ca2Nd3(SiO4)3F, is an approved mineral (IMA 2023-001) and constitutes a new member of the britholite group of the apatite supergroup. It occurs in skarn from the Malmkärra iron mine, Norberg, Västmanland (one of the Bastnäs-type deposits in Sweden), associated with calcite, dolomite, magnetite, lizardite, talc, fluorite, baryte, scheelite, gadolinite-(Nd) and other REE minerals. Fluorbritholite-(Nd) forms anhedral and small grains, rarely up to 250 µm across. They are brownish pink, transparent with a vitreous to greasy luster. The mineral is brittle, with an uneven or subconchoidal fracture, and lacks a cleavage. In thin section, the mineral is nonpleochroic, uniaxial (-). Dcalc = 4.92(1) g·cm-3 and ncalc = 1.795. The empirical chemical formula from electron microprobe (WDS) point analyses is (Ca1.62Nd0.97Ce0.83Y0.52Sm0.30Gd0.23Pr0.17La0.16Dy0.11Er0.03Tb0.03Ho0.01Yb0.01)Σ4.99(Si2.92P0.08As0.01)Σ3.01O12.00[O0.48F0.26(OH)0.14Cl0.10Br0.02]Σ1.00. The crystal structure of fluorbritholite-(Nd) was refined from single-crystal X-ray diffraction data to R1= 0.043 for 704 unique reflections. It belongs to the hexagonal system, space group P63/m, with unit cell parameters a = 9.5994(3), c = 6.9892(4) Å, V = 557.76(5) Å3 for Z = 2. Fluorbritholite-(Nd) and other britholite-group minerals are a major sink for neodymium in REE-bearing skarns of Bastnäs type.
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| 42. |
- Holtstam, Dan, 1963-, et al.
(författare)
-
Garpenbergite, Mn6□As5+Sb5+O10(OH)2, a new mineral related to manganostibite, from the Garpenberg Zn–Pb–Ag deposit, Sweden
- 2022
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 86:1, s. 1-8
-
Tidskriftsartikel (refereegranskat)abstract
- Garpenbergite is a new mineral (IMA2020-099) from the Garpenberg Norra mine, Hedemora, Dalarna, Sweden. It occurs with carlfrancisite and minor stibarsen, paradocrasite and filipstadite in a fractured skarn matrix of granular jacobsite, alleghanyite, kutnohorite and dolomite. Crystals are short-prismatic, up to 1.5 mm in length. They have a blackish to greyish brown colour, and are lustrous semi-opaque, with brown streak. Garpenbergite is brittle, with an uneven to subconchoidal fracture. Cleavage is distinct on {010}. Hardness ≈ 5 (Mohs) and VHN100 = 650(40). Dcalc = 4.47(1) g⋅cm−3 , overall ncalc = 1.85. Maximum specular reflectance values (%) obtained are 9.2 (470 nm), 9.1 (546 nm), 9.0 (589 nm) and 8.9 (650 nm). The empirical chemical formula of garpenbergite, based on electron microprobe data, is (Mn2+3.97Mg1.48Mn3+0.26Zn0.29)Σ6.00(As0.89Fe3+0.04Mn3+0.06Si0.01)Σ1.00(Sb0.98Fe0.02)Σ1.00O10[(OH)1.99Cl0.01]Σ2.00. The five strongest Bragg peaks in the powder X-ray diffraction pattern [d, Å(I, %) (hkl)] are 3.05 (30) (002), 2.665 (100) (161), 2.616 (40) (301), 2.586 (25) (251) and 1.545 (45) (462). The orthorhombic unit-cell dimensions (in Å) are a = 8.6790(9), b = 18.9057(19) and c = 6.1066(6), with V = 1001.99(18) Å3 for Z = 4. The crystal structure was refined from single-crystal X-ray diffraction data in the space-group Ibmm to R1 = 3.7% for 957 reflections. Garpenbergite, ideally Mn6As5+Sb5+O10(OH)2, is isostructural with manganostibite, Mn7AsSbO12, but possesses a cation vacancy (□) at an octahedrally coordinated structural site; the two minerals are thus related by the exchange Mn2+ + 2O2– → □ + 2(OH)– . The presence of hydroxyl groups is supported by vibration bands at 3647 and 3622 cm−1 in the Raman spectrum of garpenbergite, and by bond-valence considerations.
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| 43. |
- Holtstam, Dan, 1963-, et al.
(författare)
-
Instalment of the margarosanite group, and data on walstromite–margarosanite solid solutions from the Jakobsberg Mn–Fe deposit, Värmland, Sweden
- 2021
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 85, s. 224-232
-
Tidskriftsartikel (refereegranskat)abstract
- The margarosanite group (now officially confirmed by IMA-CNMNC) consists of triclinic Ca-(Ba, Pb) cyclosilicates with three-membered [Si3O9]6- rings (3R), with the general formula AB2Si3O9, where A = Pb, Ba, Ca and B = Ca. A closest-packed arrangement of O atoms parallel to (101) hosts Si and B cations in interstitial sites in alternating layers. The 3R layer has three independent Si sites in each ring. Divalent cations occupy three independent sites: Ca in B occupies two nonequivalent sites, Ca1 (8-fold coordinated), and Ca2 (6-fold coordinated). A (=Ca2) is occupied by Pb2+ (or Ba2+) in 6+4 coordination, or 6+1 when occupied by Ca; this third site occurs within the 3R-layer in a peripheral position. Three minerals belong to this group: margarosanite (ideally PbCa2Si3O9), walstromite (BaCa2Si3O9) and breyite (CaCa2Si3O9). So far, no solid solutions involving the Ca1 and Ca2 sites have been described. Therefore, root names depend on the composition of the Ca3 site only. Isomorphic replacement at the Ca3 sites has been noted. We here report data on a skarn sample from the Jakobsberg Mn-Fe oxide deposit, in Värmland (Sweden), representing intermediate compositions on the walstromite-margarosanite binary, in the range ca. 50–70% mol.% BaCa2Si3O9. The plumbian walstromite is closely associated with celsian, phlogopite, andradite, vesuvianite, diopside and nasonite. A crystal-structure refinement (R1 = 4.8%) confirmed the structure type, and showed that the Ca3 (Ba, Pb) site is split into two positions separated by 0.39 Å, with the Ba atoms found slightly more peripheral to the 3R-layers.
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| 44. |
- Holtstam, Dan, 1963-, et al.
(författare)
-
Langhofite, Pb2(OH)[WO4(OH)], a new mineral from Långban, Sweden.
- 2020
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 84, s. 381-389
-
Tidskriftsartikel (refereegranskat)abstract
- Langhofite, ideally Pb2(OH)[WO4(OH)], is a new mineral from the Långban mine, Värmland, Sweden. The mineral and its name were approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA2019-005). It occurs in a small vug in hematite–pyroxene skarn associated with calcite, baryte, fluorapatite, mimetite and minor sulfide minerals. Langhofite is triclinic, space group P1, and unit-cell parameters a = 6.6154(1) Å, b = 7.0766(1) Å, c = 7.3296(1) Å, α = 118.175(2)°,β = 94.451(1)°, γ = 101.146(1)° and V = 291.06(1) Å3 for Z = 2. The seven strongest Bragg peaks from powder X-ray diffractometry are[dobs, Å (I )(hkl)]: 6.04(24)(010), 3.26(22)(11-2), 3.181(19)(200), 3.079(24)(1-12), 3.016(100)(020), 2.054(20)(3-11) and 2.050(18)(13-2). Langhofite occurs as euhedral crystals up to 4 mm, elongated along the a axis, with lengthwise striation. Mohs hardness is ca. 2½,based on VHN25 data obtained in the range 130–192. The mineral is brittle, with perfect {010} and {100} cleavages. The calculated density based on the ideal formula is 7.95(1) g⋅cm–3. Langhofite is colourless to white (non-pleochroic) and transparent, with a white streakand adamantine lustre. Reflectance curves show normal dispersion, with maximum values 15.7–13.4% within 400–700 nm. Electron microprobe analyses yield only the metals Pb and W above the detection level. The presence of OH-groups is demonstrated with vibration spectroscopy, from band maxima present at ∼3470 and 3330 cm–1. A distinct Raman peak at ca. 862 cm–1 is related to symmetricW–oxygen stretching vibrations. The crystal structure is novel and was refined to R = 1.6%. It contains [W2O8(OH)2]6– edge-sharingdimers (with highly distorted WO6-octahedra) forming chains along [101] with [(OH)2Pb4]6+ dimers formed by (OH)Pb3 triangles. Chains configure (010) layers linked along [010] by long and weak Pb–O bonds, thus explaining the observed perfect cleavage on{010}. The mineral is named for curator Jörgen Langhof (b. 1965), who collected the discovery sample.
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| 45. |
- Holtstam, Dan, et al.
(författare)
-
Nomenclature of the magnetoplumbite group
- 2020
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 84:3, s. 376-380
-
Tidskriftsartikel (refereegranskat)abstract
- A nomenclature classification scheme has been approved by IMA-CNMNC for the magnetoplumbite group, with the general formula A[B12]O19. The classification on the highest hierarchical level is decided by the dominant metal at the 12-coordinated A sites, at present leading to the magnetoplumbite (A = Pb), hawthorneite (A = Ba) and hibonite (A = Ca) subgroups. Two species remain ungrouped. Most cations, with valencies from 2+ to 5+, show strong order over the five crystallographic B sites present in the crystal structure, which forms the basis for the definition of different mineral species. A new name, chihuahuaite, is introduced and replaces hibonite-(Fe).
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| 46. |
- Hålenius, Ulf, et al.
(författare)
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Gatedalite, Zr(Mn2+2Mn3+4)SiO12, a new mineral species of the braunite group from Långban, Sweden
- 2015
-
Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 79:3, s. 625-634
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Tidskriftsartikel (refereegranskat)abstract
- Gatedalite, Zr(Mn2+2Mn3+4)SiO12, is a new mineral of the braunite group. It is found in hausmannite impregnated skarn together with jacobsite, Mn-bearing calcite, tephroite, Mn-bearing phlogopite,långbanite, pinakiolite and oxyplumboroméite at the Långban Mn-Fe oxide deposit, Värmland, central Sweden. The mineral occurs as very rare, small ≤60 µm), grey, submetallic, irregularly rounded anhedral grains. Gatedalite has a calculated density of 4.783 g/cm3. It is opaque and weakly anisotropic with reflectivity in air varying between 17.1 and 20.8% in the visible spectral range. Gatedalite is tetragonal, space group I41/acd, with the unit-cell parameters a = 9.4668(6) Å , c = 18.8701(14) Å , V = 1691.1(2) Å3 and Z = 8. The crystal structure was refined to an R1 index of 5.09% using 1339 unique reflections collected with MoKa X-ray radiation. The five strongest powder X-ray diffraction lines [d in Å, (I), (hkl)] are: 2.730(100)(224), 2.367(12)(040), 1.6735(12)(440), 1.6707(29)(048) and 1.4267(16)(264). Gatedalite is a member of the braunite group (general formula AB6SiO12). It is related to braunite (Mn2+Mn3+6SiO12) through the net cation exchange (Zr4++Mn2+)➝2Mn3+, which results from the substitutions Zr4+ ➝ Mn2+ at the 8-fold coordinated site (A in the general formula) coupled with a 2Mn2+ ➝ 2Mn3+ substitution at the 6-fold coordinated sites (B in the general formula).
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| 47. |
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| 48. |
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| 49. |
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| 50. |
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