Melt densities in the CaO-FeO-Fe sub 2 O sub 3 -SiO sub 2 system and the compositional dependence of the partial molar volume of ferric iron in silicate melts

Journal Article · Thu Dec 01 00:00:00 EST 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90149-4· OSTI ID:5013997

Dingwell, D B ^[1]; Brearley, M ^[2]

---

1. Universitaet Bayreuth (West Germany)
2. Univ. of California, Los Angeles (USA)

The densities of 10 melts in the CaO-FeO-Fe{sub 2}O{sub 3}-SiO{sub 2} system were determined in equilibrium with air, in the temperature range of 1,200 to 1,550{degree}C, using the double-bob Archimedean technique. Melt compositions range from 6 to 58 wt% SiO{sub 2}, 14 to 76 wt% Fe{sub 2}O{sub 3} and 10 to 46 wt% CaO. The ferric-ferrous ratios of glasses drop-quenched from loop fusion equilibration experiments were determined by {sup 57}Fe Moessbauer spectroscopy. Melt densities range from 2.689 to 3.618 gm/cm{sup 3} with a mean standard deviation from replicate experiments of 0.15%. The volume behavior of melts in this system is significantly different from that in the Na{sub 2}O-FeO-Fe{sub 2}O{sub 3}-SiO{sub 2} system, consistent with the proposal that a proportion of Fe{sup 3+} in melts in the CaO-FeO-Fe{sub 2}O{sub 3}-SiO{sub 2} system is not tetrahedrally-coordinated by oxygen, which is supported by differences in {sup 57}Fe Moessbauer spectra of glasses. Specifically, this study confirms that the {sup 57}Fe Moessbauer spectra exhibit an area asymmetry and higher values of isomer shift of the ferric doublet that vary systematically with composition and temperature. Two species of ferric iron, varying in proportions with temperature, composition and redox state, are sufficient to describe the above observations. The presence of more than one coordination geometry for Fe{sup 3+} in low pressure silicate melts has several implications for igneous petrogenesis. The possible effects on compressibility, the pressure dependence of the redox ratio, and redox enthalpy are briefly noted.

• OSTI ID: 5013997
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 52:12; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
IGNEOUS ROCKS
IRON COMPOUNDS
PETROGENESIS
REDOX REACTIONS
STRUCTURAL CHEMICAL ANALYSIS
CALCIUM OXIDES
CHEMICAL COMPOSITION
CHEMICAL REACTION KINETICS
DENSITY
ENTHALPY
EQUILIBRIUM
GEOCHEMISTRY
IRON IONS
IRON OXIDES
MAGMA
MAGMATISM
SILICATES
SPECTROSCOPY
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CHALCOGENIDES
CHARGED PARTICLES
CHEMICAL REACTIONS
CHEMISTRY
IONS
KINETICS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
REACTION KINETICS
ROCKS
SILICON COMPOUNDS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
580000* - Geosciences