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Magnetite
About: Magnetite is a research topic. Over the lifetime, 10277 publications have been published within this topic receiving 278071 citations.
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TL;DR: The most important factors that govern compositional variations in hydrothermal magnetite are (A) temperature, (B) fluid composition, (C) oxygen and sulfur fugacity, (D) silicate and sulfide activity, (E) host rock buffering, (F) reequilibration processes, and (G) intrinsic crystallographic controls such as ionic radius and charge balance as mentioned in this paper.
399 citations
TL;DR: In this paper, the authors synthesize uniform and highly crystalline magnetite nanoparticles from the reaction of iron salts in microemulsion nanoreactors, which can be controlled from 2'nm to 10'nm by varying the relative concentrations of the iron salts, surfactant, and solvent.
Abstract: We have synthesized uniform and highly crystalline magnetite nanoparticles from the reaction of iron salts in microemulsion nanoreactors. The particle size can be controlled from 2 nm to 10 nm by varying the relative concentrations of the iron salts, surfactant, and solvent. Transmission electron microscope images of the nanoparticles reveal that they are very uniform in size distribution. Structural characterization using X-ray diffraction and X-ray magnetic circular dichroism shows that the nanoparticles are magnetite. The magnetic characterization of the nanoparticles showed that they are superparamagnetic at room temperature. Using a similar synthetic procedure, we have been able to synthesize nanoparticles of several mixed metal ferrites including cobalt ferrite, manganese ferrite, nickel ferrite, and zinc ferrite.
399 citations
TL;DR: The solubility of water in a basaltic and an andesitic melt has been determined in the pressure range from approximately 1,000 to 6,000 bars at 1,100°C as mentioned in this paper.
Abstract: The solubility of water in a basaltic and in an andesitic melt has been determined in the pressure range from approximately 1,000 to 6,000 bars at 1,100° C The solubility in basaltic melt is 31 weight percent at 1,000 bars and 94 weight percent at 6,000 bars; in the andesitic melt it is 45 weight percent at 1,000 bars and 101 weight percent at 5,300 bars The temperatures of appearance of the primary, secondary, and tertiary phases in the basalt have been determined at 1,000 bars water pressure and at the fo2's of the magnetite+hematite (MH), magnetite+fayalite+quartz (MFQ) and magnetite+wustite (MW) buffers Results are as follows:
Buffer Pyroxene Plagioclase Ore mineral
MH 1,095°C 1,065°C 1,230°C
MFQ 1,040° 1,015° 1,010°
MW 1,020° 1,010° 995°
A comparison of the solubility of water at 1,100°C and up to approximately 6,000 bars pressure in several silicate melts, ranging in composition from granitic to gabbroic, indicates that the spread of solubility is narrower than has been supposed The marked effect of fo2's on the crystallization sequence in the Columbia River basalt confirms the importance of this factor in determining liquid lines of descent In experiments with low fo2's (MW buffer) and 1,000 bars water pressure, the basalt was completely liquid at the relatively low temperature of 1,020° C
398 citations
TL;DR: In this paper, an approximate serpentine-magnetite geothermometer curve was constructed by extrapolation of observed O18 fractionations between coexisting chlorites and Fe-Ti oxides in low-grade pelitic schists whose isotopic temperatures are known from the quartz-muscovite O18 geithermometer.
Abstract: Five lizardite-chrysotile type serpentinites from California, Guatemala and the Dominican Republic show oxygen isotope fractionations of 15.1 to 12.9 per mil between coexisting serpentine and magnetite (δO18 magnetite=−7.6 to −4.6 per mil relative to SMOW). Nine antigorites (mainly from Vermont and S. E. Pennsylvania) show distinctly smaller fractionations of 8.7 to 4.8 per mil (δO18 magnetite=−2.6 to +1.7 per mil). Two lizardite and chrysotile serpentinites dredged from the Mid-Atlantic Ridge exhibit fractionations of 10.0 and 12.4 per mil (δO18 magnetite=−6.8 and −7.9 per mil, respectively), whereas an oceanic antigorite shows a value of 8.2 per mil (δO18 magnetite=−6.2). These data all clearly indicate that the antigorites formed at higher temperatures than the chrysotilelizardites. Electron microprobe analyses of magnetites from the above samples show that they are chemically homogeneous and essentially pure Fe3O2. However, some magnetites from certain other samples that show a wide variation of Cr content also give very erratic oxygen isotopic results, suggesting non-equilibrium. An approximate serpentine-magnetite geothermometer curve was constructed by (1) extrapolation of observed O18 fractionations between coexisting chlorites and Fe-Ti oxides in low-grade pelitic schists whose isotopic temperatures are known from the quartz-muscovite O18 geothermometer, and (2) estimates of the O18 fractionation factor between chlorite and serpentine (assumed to be equal to unity). This serpentine-magnetite geothermometer suggests approximate equilibrium temperatures as follows: continental lizardite-chrysotile, 85° to 115° C; oceanic lizardite and chrysotile, 130° C and 185° C, respectively; oceanic antigorite, 235° C; and continental antigorites, 220° to 460° C.
397 citations
TL;DR: In this paper, magnetite particles of average diameter 4-7 nm were prepared by precipitation in a polyvinylalcohol (PVA) aqueous solution, and the saturation magnetization of the particles was above 50 emu/g.
396 citations