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Authors: Roberts, A. P.* 
Chang, L.* 
Rowan, C. J.* 
Horng, C.* 
Florindo, F.* 
Title: Magnetic properties of sedimentary greigite (Fe3S4): an update
Issue Date: 2010
DOI: 10.1029/2010RG000336
Keywords: greigite
Subject Classification04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology 
04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating, processes, transport 
04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism 
04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism 
04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism 
Abstract: Greigite (Fe3S4) is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction. It can also grow at any time when dissolved iron and sulfide are available during diagenesis. Greigite is important in paleomagnetic, environmental, biological, biogeochemical, tectonic, and industrial processes. Much recent progress has been made in understanding its magnetic properties. Greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites. The crystallographic c-axis is the easy axis of magnetization, with magnetic properties dominated by magnetocrystalline anisotropy. Robust empirical estimates of the saturation magnetization, anisotropy constant, and exchange constant for greigite have been obtained recently for the first time, and the first robust estimate of the low-field magnetic susceptibility is reported here. The Curie temperature of greigite remains unknown, but must exceed 350°C. Greigite lacks a low-temperature magnetic transition. Based on preliminary micromagnetic modeling, the size range for stable single domain behavior is 17-200 nm for cubic crystals and 17-500 nm for octahedral crystals. Gradual variation in magnetic properties is observed through the pseudo-single domain size range. We systematically document the known magnetic properties of greigite (at high, ambient and low temperatures, and with alternating and direct fields) and illustrate how grain size variations affect magnetic properties. Recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite, which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records, including widespread remagnetizations.
Description: Accepted for publication in Reviews of Geophysics. Copyright (2010) American Geophysical Union
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