| 1. |
- Sallstedt, Therese, et al.
(författare)
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Instant Attraction : Clay Authigenesis in Fossil Fungal Biofilms
- 2019
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Ingår i: Geosciences. - Basel : MDPI. - 2076-3263. ; 9:9, s. 1-21
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Forskningsöversikt (refereegranskat)abstract
- Clay authigenesis associated with the activity of microorganisms is an important process for biofilm preservation and may provide clues to the formation of biominerals on the ancient Earth. Fossilization of fungal biofilms attached to vesicles or cracks in igneous rock, is characterized by fungal-induced clay mineralization and can be tracked in deep rock and deep time, from late Paleoproterozoic (2.4 Ga), to the present. Here we briefly review the current data on clay mineralization by fossil fungal biofilms from oceanic and continental subsurface igneous rock. The aim of this study was to compare the nature of subsurface fungal clays from different igneous settings to evaluate the importance of host rock and ambient redox conditions for clay speciation related to fossil microorganisms. Our study suggests that the most common type of authigenic clay associated with pristine fossil fungal biofilms in both oxic (basaltic) and anoxic (granitic) settings are montmorillonite-like smectites and confirms a significant role of fungal biofilms in the cycling of elements between host rock, ocean and secondary precipitates. The presence of life in the deep subsurface may thus prove more significant than host rock geochemistry in directing the precipitation of authigenic clays in the igneous crust, the extent of which remains to be fully understood.
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| 2. |
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| 3. |
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| 4. |
- Ali, Sk Imran, et al.
(författare)
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Synthesis and Magnetic Properties of the Ternary Oxofluoride Fe3Sb4O6F6
- 2020
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; 2020:39, s. 3746-3752
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Tidskriftsartikel (refereegranskat)abstract
- The new compound Fe(3)Sb(4)O(6)F(6)was prepared by hydrothermal synthesis and its crystal structure was determined from single-crystal X-ray diffraction data. The synthesis was made under slightly basic conditions to prevent oxidation of Fe(2+)to Fe3+. The compound crystallizes in the cubic space groupI-43mwith separate crystallographic sites for Fe(2+)and Sb3+. Fe(3)Sb(4)O(6)F(6)is isostructural with M3Sb4O6F6(M = Co, Ni, Zn). The crystal structure is comprising distorted [FeO2F4] octahedra connected via corner sharing at F-atoms and [SbO3] trigonal pyramids that form [Sb4O6] units that connect via O-atoms to the Fe-atoms. Mossbauer spectroscopy measurements on the hydrothermal synthesis products prove the majority phase contains Fe in the oxidation state +2. Powder X-ray diffraction suggests that an additional phase of the Mossbauer sample containing Fe(3+)can be attributed to FeSbO(2)F(2)as secondary phase. Fe(3)Sb(4)O(6)F(6)exhibits antiferromagnetic order below ca. 72 K succeeded by a second magnetic phase transition at ca. 30 K. Strong antiferromagnetic spin-exchange interaction is attributed to 180 degrees Fe-F-Fe superexchange pathways identified in the crystal structure.
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| 5. |
- Allard, Bert, 1945-, et al.
(författare)
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Metal Exchangeability in the REE-Enriched Biogenic Mn Oxide Birnessite from Ytterby, Sweden
- 2023
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 13:8
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Tidskriftsartikel (refereegranskat)abstract
- A black substance exuding from fractures was observed in 2012 in Ytterby mine, Sweden, and identified in 2017 as birnessite with the composition Mx[Mn(III,IV)](2)O-4 center dot(H2O)n. M is usually calcium and sodium, with x around 0.5. The Ytterby birnessite is unique, with M being calcium, magnesium, and also rare earth elements (REEs) constituting up to 2% of the total metal content. The biogenic origin of the birnessite was established in 2018. Analysis of the microbial processes leading to the birnessite formation and the REE enrichment has continued since then. The process is fast and dynamic, as indicated by the depletion of manganese and of REE and other metals in the fracture water during the passage over the precipitation zone in the mine tunnel. Studies of the exchangeability of metals in the structure are the main objective of the present program. Exposure to solutions of sodium, calcium, lanthanum, and iron led to exchanges and altered distribution of the metals in the birnessite, however, generating phases with almost identical structures after the exchanges, and no new mineral phases were detected. Exchangeability was more efficient for trivalent elements (REE) over divalent (calcium) and monovalent (sodium) elements of a similar size (ionic radii 90-100 pm).
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| 6. |
- Allard, Bert, et al.
(författare)
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On the formation and metal exchangeability of the rare earth element enriched birnessite from the Ytterby mine, Sweden
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A porous black substance exuding from fractures in an underground tunnel leading to the shaft of the Ytterby mine, Sweden, was observed in 2012 and characterized as a secondary manganese (Mn) oxide in 2015. The oxide was identified in 2017 as a birnessite variety, Mx[Mn(III,IV)]2O4∙(H2O)n where M usually is Ca, Na and x is around 0.5, but the Ytterby birnessite appears to be unique with M being Ca, Mg but also yttrium and rare earth elements (YREE), constituting up to 2% of the metal content. The biogenic origin of the Ytterby birnessite was established in 2018. Studies of the formation of this unique birnessite phase has progressed during 2018-19 with detailed studies of the hydrochemistry of the fracture water as well of the exchangeability of the metals M in the structure: Na, Ca, Fe and La representing the YREE. Exposure to solutions of Na, Ca, Fe, and La, respectively (1 M) led to exchanges and altered distribution of the metals constituting M, with a preference of YREE (trivalent) over Ca (divalent) over Na (monovalent), all of similar ionic radii, as well as higher affinity for YREE over Fe(III), being smaller. Fe(III) did not replace Mn(III) in the structure, despite the fact that their radii are almost identical. No discrete new Fe phase was indicated, and the structure of the birnessite phase was almost identical after exchanges of M, as indicated from XRD. The formation of birnessite in the fracture opening on the tunnel wall appears to be a fast and dynamic process, as indicated by a significant depletion of Mn as well as of YREE in the fracture water during the passage over the precipitation zone, from top to bottom.
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| 7. |
- 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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| 8. |
- 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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