Publication Date:
2012-02-03
Description:
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. On the basis of 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:
Published
Description:
RG1002
Description:
2.2. Laboratorio di paleomagnetismo
Description:
JCR Journal
Description:
restricted
Keywords:
greigite
;
04. 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
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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