Reductive dissolution of biogenic magnetite

Abstract Reductive dissolution of magnetite is known to occur below the Fe-redox boundary in sediments. In this study, detailed processes associated with biogenic magnetite dissolution are documented. A sediment core from the Japan Sea was used for this purpose, in which reductive dissolution of magnetic minerals is known to start at depths of about 1.15 m and is mostly complete within a depth interval of about 0.35 m. Using first-order reversal curve diagrams, preferential dissolution of biogenic magnetite within this interval is estimated from the observation that a narrow peak that extends along the coercivity axis (central ridge), which is indicative of biogenic magnetite, diminishes downcore. Transmission electron microscopy is used to demonstrate that the sediments contain three magnetofossil morpho-types: octahedra, hexagonal prisms, and bullet-shaped forms. Within the reductive dissolution zone, partially etched crystals are commonly observed. With progressive dissolution, the proportion of bullet-shaped magnetofossils decreases, whereas hexagonal prisms become more dominant. This observation can be explained by the differences in resistance to dissolution among crystal planes of magnetite and the differences in surface area to volume ratios. Magnetofossil morphology may reflect the preference of magnetotactic bacterial lineages for inhabiting specific chemical environments in sediments. However, it could also reflect alteration of the original morphological compositions during reductive diagenesis, which should be considered when using magnetofossil morphology as a paleoenvironmental proxy.

Download Full-text

Reductive dissolution of biogenic magnetite

10.21203/rs.3.rs-50707/v3 ◽

2020 ◽

Author(s):

Toshitsugu Yamazaki

Keyword(s):

Japan Sea ◽

Depth Interval ◽

Reductive Dissolution ◽

Magnetic Minerals ◽

Specific Chemical ◽

Biogenic Magnetite ◽

Transmission Electron ◽

Dissolution Zone ◽

Central Ridge ◽

Redox Boundary

Abstract Reductive dissolution of magnetite is known to occur below the Fe-redox boundary in sediments. In this study detailed processes associated with biogenic magnetite dissolution are documented. A sediment core from the Japan Sea was used for this purpose, in which reductive dissolution of magnetic minerals is known to start at depths of about 1.15 m and is mostly complete within a depth interval of about 0.35 m. Using first-order reversal curve diagrams, preferential dissolution of biogenic magnetite within this interval is estimated from the observation that a narrow peak that extends along the coercivity axis (central ridge), which is indicative of biogenic magnetite, diminishes downcore. Transmission electron microscopy is used to demonstrate that the sediments contain three magnetofossil morpho-types: octahedra, hexagonal prisms, and bullet-shaped forms. Within the reductive dissolution zone, partially etched crystals are commonly observed. With progressive dissolution, the proportion of bullet-shaped magnetofossils decreases, whereas hexagonal prisms become more dominant. This observation can be explained by the differences in resistance to dissolution among crystal planes of magnetite and the differences in surface area to volume ratios. Magnetofossil morphology may reflect the preference of magnetotactic bacterial lineages for inhabiting specific chemical environments in sediments. However, it could also reflect alteration of the original morphological compositions during reductive diagenesis, which should be considered when using magnetofossil morphology as a paleoenvironmental proxy.

Download Full-text

Reductive dissolution of biogenic magnetite

10.21203/rs.3.rs-50707/v2 ◽

2020 ◽

Author(s):

Toshitsugu Yamazaki

Keyword(s):

Japan Sea ◽

Depth Interval ◽

Reductive Dissolution ◽

Magnetic Minerals ◽

Specific Chemical ◽

Biogenic Magnetite ◽

Transmission Electron ◽

Dissolution Zone ◽

Central Ridge ◽

Redox Boundary

Download Full-text

Reductive dissolution of biogenic magnetite

10.21203/rs.3.rs-50707/v1 ◽

2020 ◽

Author(s):

Toshitsugu Yamazaki

Keyword(s):

Japan Sea ◽

Reductive Dissolution ◽

Hexagonal Prism ◽

Magnetic Minerals ◽

Surface Areas ◽

Biogenic Magnetite ◽

Transmission Electron ◽

Central Ridge ◽

Chemical Conditions ◽

Redox Boundary

Abstract Reductive dissolution of magnetites is known to occur below the Fe-redox boundary in sediment columns. This study aims to document the detailed processes of biogenic magnetite dissolution. A sediment core taken from the Japan Sea was used for this purpose, in which reductive dissolution of magnetic minerals are known to start at about 1.3 m in depth and mostly complete within an interval of about 0.3 m. Using first-order reversal curve diagrams, preferential dissolution of biogenic magnetites within this interval is estimated from the observation that a narrow peak extending along the coercivity axis (the central ridge), which is indicative of biogenic magnetite, diminishes downcore. Transmission electron microscopy shows that the sediments contain the three morpho-types of magnetofossils: octahedron, hexagonal prism, and bullet shaped. With the progress of reductive dissolution, the proportion of bullet-shaped magnetofossils decreases, whereas that of hexagonal prisms increases. For hexagonal prisms, {111} caps are often etched while {110} side faces are almost intact. These observations can be explained by the differences in resistivity against dissolution among crystal planes of magnetite. A previous study reported that the dissolution rate of (111) planes is higher than that of (110) planes. Hexagonal prisms elongate in the [111] direction and are wrapped with {110} side faces, whereas octahedral and bullet-shaped magnetofossils have larger proportions of surface areas with {111} faces. Magnetosome morphology may reflect preference of inhabiting magnetotactic bacterial lineage for chemical conditions in sediments. One should, however, be cautious for possible alteration of original morphological composition during reductive diagenesis when magnetofossil morphology is used as a paleoenvironmental proxy.

Download Full-text

Preferential dissolution along misoriented boundaries in heterogenite

MRS Proceedings ◽

10.1557/proc-620-m5.7.1 ◽

2000 ◽

Vol 620 ◽

Author(s):

R. Lee Penn ◽

Alan T. Stone ◽

David R. Veblen

Keyword(s):

Electron Microscopy ◽

Aspect Ratio ◽

Reductive Dissolution ◽

Morphology Evolution ◽

Crystal Chemical ◽

Transmission Electron ◽

Micron Size ◽

Primary Particles ◽

Size And Morphology ◽

Preferential Dissolution

ABSTRACTHigh-Resolution Transmission Electron Microscopy (HRTEM) results show a strong crystal-chemical and defect dependence on the mode of dissolution of synthetic heterogenite (CoOOH) particles. As-synthesized heterogenite particles are micron-size plates (aspect ratio ∼ 1/30) constructed of crystallographically oriented ∼ 3-nm primary particles or are single ∼ 21-nm unattached heterogenite platelets (aspect ratio ∼1/7). Reductive dissolution, using hydroquinone, was examined in order to evaluate morphology evolution as a function of reductant concentration. Two end-member modes of dissolution were observed: 1) non-specific dissolution of macroparticles and 2) preferential dissolution along misoriented boundaries. In the case of non-specific dissolution, average macrocrystal size and morphology are not altered as building block crystals are consumed. The result is web-like particles with similar breadth and shape as undissolved particles. Preferential dissolution involves the formation of channels or holes along boundaries of angular misorientation. Such boundaries involve only a few degrees of tilt, but dissolution occurs almost exclusively at such sites. Energy-Filtered TEM thickness maps show that the thickness of surrounding material is not significantly different from that of undissolved particles. Finally, natural heterogenite from Goodsprings, Nevada, shows morphology and microstructure similar to those of this synthetic heterogenite.

Download Full-text

Development of New Marker Compounds for the Detection of Chemical Element Labels by Electron Spectroscopic Imaging (ESI)

Microscopy and Microanalysis ◽

10.1017/s1431927600031263 ◽

2001 ◽

Vol 7 (S2) ◽

pp. 1038-1039

Author(s):

S. Raddatz ◽

E. P. Mark ◽

A. Haking ◽

W. Probst ◽

M. Wiessler ◽

...

Keyword(s):

Electron Microscopy ◽

Chemical Element ◽

Three Dimensional ◽

Point Of View ◽

High Concentration ◽

Specific Chemical ◽

Energy Filtering ◽

Transmission Electron ◽

Gold Particle Size ◽

Marker Compounds

A promising aspect of ESI is its application in the detection of elemental labels introduced into biomolecules for cell and molecular biological techniques. Even though colloidal gold labeling for electron microscopy (EM) is highly developed, availability of alternative labels, especially for double or triple labeling applications would be helpful because of difficulties with gold concerning i) detection (gold diameters ≤1nm), ii) discrimination due to gold particle size variations in one size class, and iii) different labeling efficiencies depending on gold granule size. An alternative labeling molecule should contain a high concentration of a specific chemical element which is not or in minor concentrations present in the system under surveillance, and has to have the potential to be discriminated from “biological” elements by ESI.With respect to ESI, one candidate for elemental labeling is boron. It meets the criteria described above and substantial experience in the synthesis of labeling compounds exists. From the chemical point of view, the preferred labeling structure is a so called dendrimer, a highly branched regular three-dimensional monodisperse macromolecule. Dendritic structures offer a large variety of functionalities to incorporate an element detectable by energy filtering transmission electron microscopy (EFTEM).

Download Full-text

Novel Colloidal Assembly Methods for the Preparation of Core-Shell Composite Materials

MRS Proceedings ◽

10.1557/proc-636-d9.17.1 ◽

2000 ◽

Vol 636 ◽

Author(s):

Michael S. Fleming ◽

Tarun K. Mandal ◽

David R. Walt

Keyword(s):

Electron Microscopy ◽

Electrostatic Interactions ◽

Physical Adsorption ◽

Polymer Nanoparticles ◽

Biological Interactions ◽

Specific Chemical ◽

Capillary Action ◽

Colloidal Assembly ◽

Transmission Electron ◽

Shell Composite

AbstractColloidal assembly is a process by which particles ranging in size from nanometers to micrometers are organized into structures by mixing two or more particle types. Assembly is controlled by either specific or non-specific interactions between particles. Examples include chemical bonding, biological interactions, electrostatic interactions, capillary action and physical adsorption. The assembly process is performed such that smaller particles assemble around larger ones. In this paper, we report on colloidal assembly of polymer nanoparticles (50-200 nm diameter) onto silica particles (3-5 μm diameter) using specific chemical interactions (i.e. aminealdehyde). Annealing the assembled composites at temperatures above the glass transition (Tg) of the polymer nanospheres allows polymer to flow and uniformly coat the microsphere surfaces. Polystyrene and poly(methyl methacrylate) nanospheres were used to produce such materials. Shell composites were created by mixing both nanosphere types prior to assembly/annealing. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the materials presented herein.

Download Full-text

Transmission electron microscopy of magnetic minerals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100109550 ◽

1978 ◽

Vol 36 (1) ◽

pp. 482-483

Author(s):

P.P.K. Smith

Keyword(s):

Critical Size ◽

Magnetic State ◽

Magnetic Domain ◽

Continental Drift ◽

Axial Ratio ◽

Igneous Rocks ◽

Interacting Particles ◽

Magnetic Minerals ◽

The Earth ◽

Transmission Electron

The study of palaeomagnetism has had a great impact on the earth sciences, providing the first conclusive proof that continental drift has occurred. Although it is generally accepted that the primary magnetisation of basic igneous rocks is a thermal remanent magnetisation (TRM) carried by opaque iron-titanium oxide minerals, particularly those of the magnetite-ulvospinel series, there is still some doubt as to the exact magnetic state of the grains responsible for this palaeomagnetic TRM. The great stability of the TRM in many igneous rocks suggests a population of non-interacting particles, each consisting of a single magnetic domain, but it has been argued that the grain size of magnetic minerals in rocks is much greater than the critical size for this behaviour. For magnetite this critical size is about 0. 05 μm for equidimensional particles, rising to about 1 μm for elongated grains with an axial ratio of 10 : 1 (Evans, 1972). Thus single-domain particles would not be detected by conventional (optical) petrographic techniques.

Download Full-text

Opportunities for Chromatic Aberration Corrected High-Resolution Transmission Electron Microscopy, Lorentz Microscopy and Electron Holography of Magnetic Minerals

Microscopy and Microanalysis ◽

10.1017/s1431927612010392 ◽

2012 ◽

Vol 18 (S2) ◽

pp. 1708-1709 ◽

Cited By ~ 6

Author(s):

R. Dunin-Borkowski ◽

L. Houben ◽

J. Barthel ◽

A. Thust ◽

M. Luysberg ◽

...

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

High Resolution ◽

Chromatic Aberration ◽

Electron Holography ◽

Magnetic Minerals ◽

Lorentz Microscopy ◽

Transmission Electron ◽

Aberration Corrected

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Download Full-text

Suberized Cell Walls of Cork from Cork Oak Differ from Other Species

Microscopy and Microanalysis ◽

10.1017/s1431927610093839 ◽

2010 ◽

Vol 16 (5) ◽

pp. 569-575 ◽

Cited By ~ 13

Author(s):

Rita Teresa Teixeira ◽

Helena Pereira

Keyword(s):

Secondary Wall ◽

Three Dimensional ◽

Spatial Location ◽

Typical Feature ◽

Quercus Suber ◽

Uranyl Acetate ◽

Calotropis Procera ◽

Specific Chemical ◽

Transmission Electron ◽

Species Specific

AbstractPlants have suberized cells that act as protective interfaces with the environment or between different plant tissues. A lamellar structure of alternating dark and light bands has been found upon transmission electron microscopy (TEM) observation of cork cells and considered a typical feature of the suberized secondary wall. We observed cork cells from periderms of Quercus suber, Quercus cerris, Solanum tuberosum, and Calotropis procera by TEM after uranyl acetate and lead citrate staining. A lamellated structure was observed in S. tuberosum and C. procera but not in Q. suber and Q. cerris where the suberized cell wall showed a predominantly hyaline aspect with only a dark dotted staining. Removal of suberin from Q. suber cells left a thinner secondary wall that lost the translucent aspect. We hypothesize that the species' specific chemical composition of suberin will result in different three-dimensional macromolecular development and in a different spatial location of lignin and other aromatics. A lamellated ultrastructure is therefore not a general feature of suberized cells.

Download Full-text

The identification of magnetic minerals and other selfassembled structures within magnetotactic bacteria using Electron Microscopy and related micro-techniques

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100129747 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1022-1023

Author(s):

Dennis A. Bazylinski ◽

Anthony J. Garratt-Reed ◽

Richard B. Frankel

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Magnetic Behavior ◽

Magnetotactic Bacteria ◽

Structural Features ◽

Magnetic Minerals ◽

Intracellular Iron ◽

Selected Area Electron Diffraction ◽

Transmission Electron ◽

Scanning Transmission

Magnetotactic bacteria are a diverse group of procaryotes whose direction of motility is influenced by magnetic fields. These organisms are ubiquitous in aquatic habitats and contain unique intracellular iron-rich membrane-bounded inclusions called magnetosomes that are responsible for the cells’ magnetic behavior. The composition, size (40-100 nm), morphology, position, and orientation of the particles appear to be highly controlled by these bacteria. Ferrimagnetic magnetite (Fe3O4), greigite (Fe3S4), and pyrrhotite (Fe7S8) and nonmagnetic pyrite (FeS2) have been identified as the mineral phases of the magnetosomes in different bacteria. These organisms also contain other intracellular structures that reflect aspects of their physiology, metabolism, and ecology. In order to determine the external structural features of cells and the composition and structure of their intracellular inclusions, transmission electron microscopy (TEM), scanning-transmission electron microscopy (STEM), energy-dispersive x-ray detection (EDXA), and selected area electron diffraction (SAED) techniques were employed.The results of a typical electron microscope (EM) and microanalytical study of a Fe3O4-producing magnetotactic bacterium is shown in Figures 1-4. This unidentified organism, designated strain MV-4, was isolated from sulfide-rich water and sediment collected from a salt marsh.

Download Full-text