XPS evidence for Fe and As oxidation states and electronic states in loellingite (FeAs2)
-
R.A. Jones
Abstract
This first X-ray Photoelectron Spectroscopy (XPS) study of loellingite (FeAs2) reveals a strong Fe 2p3/2 singlet peak at 707.0 eV signifying that fully coordinated Fe of the bulk phase has the same oxidation state of bulk Fe in marcasite, arsenopyrite, and pyrite. The As 3d peak of loellingite (41.1 eV) demonstrates that As atoms of As dimers in loellingite have the same oxidation state as As atoms of As-S dimers in arsenopyrite. These XPS data consequently corroborate previous Mössbauer studies and confirm theoretical considerations; Fe of loellingite, arsenopyrite, and marcasite is divalent (formally) rather than being trivalent (arsenopyrite) or tetravalent (loellingite). Arsenic is present as As1- (formal oxidation state) in both loellingite and arsenopyrite.
The presence of an intense Fe 2p3/2 singlet peak for loellingite, rather than a multiplet set of peaks, demonstrates that all valence electrons of Fe in the bulk phase are paired; loellingite is a diamagnetic material thus resolving issues related to magnetic studies of the mineral. A multiplet set of peaks explains the weak high binding energy tail of the Fe 2p3/2 spectrum. This set of peaks is derived from Fe surface species. As for pyrite surfaces, Fe surface sites are of C4v symmetry due to loss of a ligand during fracture. The symmetry stabilizes the dz² orbital leading to an intermediate spin state with unpaired electrons in Fe valence orbitals and a multiplet set of peaks. A second, weak set of multiplet peaks, probably representing Fe3+ bonded to As are also present, suggesting that a minor proportion of surface Fe2+ and arsenic undergo an auto-redox reaction in response to fracture.
The As 3d spectrum includes two spin-orbit-split doublets. One doublet represents As of As-As dimers located within the bulk phase (fully coordinated). The second is located at somewhat greater binding energy than the bulk contribution and may represent a surface polymeric As contribution.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- The chemical character of fluids forming diagenetic illite in the Southern Appalachian Basin
- Interpretation of K-Ar dates of illitic clays from sedimentary rocks aided by modeling
- Illite polytype quantification for accurate K-Ar age determination
- Characterization and modeling of illite crystal particles and growth mechanisms in a zoned hydrothermal deposit, Lake City, Colorado
- Characterization of the Waukesha Illite: A mixed-polytype illite in the Clay Mineral Society repository
- Exploring intra-crystalline B-isotope variations in mixed-layer illite-smectite
- Characteristics of mixed-layer smectite/illite density separates during burial diagenesis
- I-S precipitation in pore space as the cause of geopressuring in Mesozoic mudstones, Egersund Basin, Norwegian continental shelf
- Structural and chemical heterogeneity of illite-smectites from Upper Jurassic mudstones of East Greenland related to volcanic and weathered parent rocks
- Berthierine/chamosite, corrensite, and discrete chlorite from evolved verdine and evaporite-associated facies in the Jurassic Sundance Formation, Wyoming
- Weathering of ilmenite from granite and chlorite schist in the Georgia Piedmont
- The effects of grinding on the structure of a low-defect kaolinite
- Structure of heavy-metal sorbed birnessite: Part 1. Results from X-ray diffraction
- Structure of heavy-metal sorbed birnessite: Part 2. Results from electron diffraction
- Structure of synthetic Na-birnessite: Evidence for a triclinic one-layer unit cell
- New modeling of X-ray diffraction by disordered lamellar structures, such as phyllosilicates
- Identification of polytypic groups in hydrous phyllosilicates using electron backscattering patterns
- Orientational order-disorder of N(D,H)4+ in tobelite
- XPS evidence for Fe and As oxidation states and electronic states in loellingite (FeAs2)
- Hydrothermal alteration of olivine in a flow-through autoclave: Nucleation and growth of serpentine phases
- The influence of bulk composition on the diffusivity of carbon dioxide in Na aluminosilicate melts
- A combined rapid-quench and H2-membrane setup for internally heated pressure vessels: Description and application for water solubility in basaltic melts
- Letter. Crystal morphology of MV-1 magnetite
Articles in the same Issue
- The chemical character of fluids forming diagenetic illite in the Southern Appalachian Basin
- Interpretation of K-Ar dates of illitic clays from sedimentary rocks aided by modeling
- Illite polytype quantification for accurate K-Ar age determination
- Characterization and modeling of illite crystal particles and growth mechanisms in a zoned hydrothermal deposit, Lake City, Colorado
- Characterization of the Waukesha Illite: A mixed-polytype illite in the Clay Mineral Society repository
- Exploring intra-crystalline B-isotope variations in mixed-layer illite-smectite
- Characteristics of mixed-layer smectite/illite density separates during burial diagenesis
- I-S precipitation in pore space as the cause of geopressuring in Mesozoic mudstones, Egersund Basin, Norwegian continental shelf
- Structural and chemical heterogeneity of illite-smectites from Upper Jurassic mudstones of East Greenland related to volcanic and weathered parent rocks
- Berthierine/chamosite, corrensite, and discrete chlorite from evolved verdine and evaporite-associated facies in the Jurassic Sundance Formation, Wyoming
- Weathering of ilmenite from granite and chlorite schist in the Georgia Piedmont
- The effects of grinding on the structure of a low-defect kaolinite
- Structure of heavy-metal sorbed birnessite: Part 1. Results from X-ray diffraction
- Structure of heavy-metal sorbed birnessite: Part 2. Results from electron diffraction
- Structure of synthetic Na-birnessite: Evidence for a triclinic one-layer unit cell
- New modeling of X-ray diffraction by disordered lamellar structures, such as phyllosilicates
- Identification of polytypic groups in hydrous phyllosilicates using electron backscattering patterns
- Orientational order-disorder of N(D,H)4+ in tobelite
- XPS evidence for Fe and As oxidation states and electronic states in loellingite (FeAs2)
- Hydrothermal alteration of olivine in a flow-through autoclave: Nucleation and growth of serpentine phases
- The influence of bulk composition on the diffusivity of carbon dioxide in Na aluminosilicate melts
- A combined rapid-quench and H2-membrane setup for internally heated pressure vessels: Description and application for water solubility in basaltic melts
- Letter. Crystal morphology of MV-1 magnetite
