Behavior of cation vacancy in kenotetrahedral Cr-spinels from Albanian eastern belt ophiolites
-
Ferdinando Bosi
,
Giovanni B. Andreozzi
Abstract
The crystal chemistry of 17 Cr-spinels from the Albanian eastern belt ophiolites was studied by a multi-analytical approach (EMPA, MS, SREF), processing the data with a tested optimization model to obtain site populations. The samples come from the three most important ultramafic massifs of Albania (Tropoja, Bulqiza, and Shebenik), and occur in ultramafic cumulates as well as in ultramafic mantle tectonites, associated with serpentinized olivine. All samples are characterized by Cr ↔ Al and minor Mg ↔ Fe2+ substitutions, and may be classified as magnesiochromite, except one, which is spinel s.s. Cation distributions showed that Cr and Al are ordered in M, and Fe2+ and Mg in the T site. Contents of Fe3+ measured by MS were always higher than those calculated from EMPA, and this non-stoichiometry reveals that the Albanian crystals underwent an increase in fO₂ conditions after mineral formation. Cation vacancies produced by Fe2+ oxidation occur in the T site, and the oxidation mechanism, is described by:
2 TFe2+ + ½ O2 → 2 TFe3+ + O2- + T⃞.
T-O variations show a non-linear regression with TFe2+, and this trend is due to both the cooperative effects of TMg ↔ TFe2+ substitution and TFe2+ oxidation. Cation vacancy in the T site does not impart rigidity to the polyhedron, because it cannot have chemical bonds with ligands: this feature, together with the spinel topology, makes the tetrahedron adopt .soft. behavior. In effect, the T⃞-O distance does not have a single value, but changes according to the population of the M site, as confirmed by comparison with literature data and also by application of the Bond Valence Model.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- The origin of the color of pearls in iridescence from nano-composite structures of the nacre
- “Invisible„ gold revealed: Direct imaging of gold nanoparticles in a Carlin-type deposit
- Behavior of cation vacancy in kenotetrahedral Cr-spinels from Albanian eastern belt ophiolites
- Displacement and strain fields around a [100] dislocation in olivine measured to sub-angstrom accuracy
- Kiglapait mineralogy IV: The augite series
- Metasomatic formation of kosmochlor-bearing diopside in peridotite xenoliths from North Island, New Zealand
- Determination of standard thermodynamic properties of sulfides in the Ag-Au-S system by means of a solid-state galvanic cell
- Hydroxyl ordering in igneous apatite
- Accommodation of the carbonate ion in apatite: An FTIR and X-ray structure study of crystals synthesized at 2–4 GPa
- Mg/Si ratios of aqueous fluids coexisting with forsterite and enstatite based on the phase relations in the Mg2SiO4-SiO2-H2O system
- The activity of silica, water, and the equilibration of intermediate and silicic magmas
- The CO2–H2O system: IV. Empirical, isothermal equations for representing vapor-liquid equilibria at 110–350 °C, P ≤ 150 MPa
- Repercussions of size heterogeneity on the measurement of specific surface areas of colloidal minerals: Combination of macroscopic and microscopic analyses
- The crystal-structure of synthetic NaNa2Mg5Si8O21(OH)3, a triclinic C1̄ amphibole with a triple-cell and excess hydrogen
- High-pressure phase transitions in Ca0.2Sr0.8Al2Si2O8feldspar
- Phase transition of Ca-perovskite and stability of Al-bearing Mg-perovskite in the lower mantle
- Mineralogy and petrology of a mullite-bearing pseudotachylyte: Constraints on the temperature of coseismic frictional fusion
- New developments in two-feldspar thermometry
- Ordered distribution of Au and Ag in the crystal structure of muthmannite, AuAgTe2, a rare telluride from Sacarîmb, western Romania
- Polytypism of cookeite in low-grade metapelites of the Cameros Basin, Spain: Lack of correlation of well-ordered polytypes with pressure
- Evolution of mineral compositions during eclogitization of subducting basaltic crust
- Mass balance during retrogression of eclogite-facies minerals in the Rongcheng eclogite, eastern Sulu ultrahigh-pressure terrane, China
- Synthesis of REE and Y phosphates by Pb-free flux methods and their utilization as standards for electron microprobe analysis and in design of monazite chemical U-Th-Pb dating protocol
- The chemistry and crystal structure of okanoganite-(Y) and comparison with vicanite-(Ce)
- An automated system for phase identification and quantitative composition determination using the electron microprobe: Theory and applications
- Piston-cylinder calibration at 400 to 500 MPa: A comparison of using water solubility in albite melt and NaCl melting
- Letter. Comparative planetary mineralogy: V/(Cr + Al) systematics in chromite as an indicator of relative oxygen fugacity
- Letter. Porous titanosilicate nanorods in the structure of yuksporite, (Sr,Ba)2K4(Ca,Na)14(⃞,Mn,Fe) {(Ti,Nb)4(O,OH)4[Si6O17]2[Si2O7]3}(H2O,OH)n, resolved using synchrotron radiation
Articles in the same Issue
- The origin of the color of pearls in iridescence from nano-composite structures of the nacre
- “Invisible„ gold revealed: Direct imaging of gold nanoparticles in a Carlin-type deposit
- Behavior of cation vacancy in kenotetrahedral Cr-spinels from Albanian eastern belt ophiolites
- Displacement and strain fields around a [100] dislocation in olivine measured to sub-angstrom accuracy
- Kiglapait mineralogy IV: The augite series
- Metasomatic formation of kosmochlor-bearing diopside in peridotite xenoliths from North Island, New Zealand
- Determination of standard thermodynamic properties of sulfides in the Ag-Au-S system by means of a solid-state galvanic cell
- Hydroxyl ordering in igneous apatite
- Accommodation of the carbonate ion in apatite: An FTIR and X-ray structure study of crystals synthesized at 2–4 GPa
- Mg/Si ratios of aqueous fluids coexisting with forsterite and enstatite based on the phase relations in the Mg2SiO4-SiO2-H2O system
- The activity of silica, water, and the equilibration of intermediate and silicic magmas
- The CO2–H2O system: IV. Empirical, isothermal equations for representing vapor-liquid equilibria at 110–350 °C, P ≤ 150 MPa
- Repercussions of size heterogeneity on the measurement of specific surface areas of colloidal minerals: Combination of macroscopic and microscopic analyses
- The crystal-structure of synthetic NaNa2Mg5Si8O21(OH)3, a triclinic C1̄ amphibole with a triple-cell and excess hydrogen
- High-pressure phase transitions in Ca0.2Sr0.8Al2Si2O8feldspar
- Phase transition of Ca-perovskite and stability of Al-bearing Mg-perovskite in the lower mantle
- Mineralogy and petrology of a mullite-bearing pseudotachylyte: Constraints on the temperature of coseismic frictional fusion
- New developments in two-feldspar thermometry
- Ordered distribution of Au and Ag in the crystal structure of muthmannite, AuAgTe2, a rare telluride from Sacarîmb, western Romania
- Polytypism of cookeite in low-grade metapelites of the Cameros Basin, Spain: Lack of correlation of well-ordered polytypes with pressure
- Evolution of mineral compositions during eclogitization of subducting basaltic crust
- Mass balance during retrogression of eclogite-facies minerals in the Rongcheng eclogite, eastern Sulu ultrahigh-pressure terrane, China
- Synthesis of REE and Y phosphates by Pb-free flux methods and their utilization as standards for electron microprobe analysis and in design of monazite chemical U-Th-Pb dating protocol
- The chemistry and crystal structure of okanoganite-(Y) and comparison with vicanite-(Ce)
- An automated system for phase identification and quantitative composition determination using the electron microprobe: Theory and applications
- Piston-cylinder calibration at 400 to 500 MPa: A comparison of using water solubility in albite melt and NaCl melting
- Letter. Comparative planetary mineralogy: V/(Cr + Al) systematics in chromite as an indicator of relative oxygen fugacity
- Letter. Porous titanosilicate nanorods in the structure of yuksporite, (Sr,Ba)2K4(Ca,Na)14(⃞,Mn,Fe) {(Ti,Nb)4(O,OH)4[Si6O17]2[Si2O7]3}(H2O,OH)n, resolved using synchrotron radiation
