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High-pressure elasticity of a natural magnetite crystal

Hans J. Reichmann and Steven D. Jacobsen
High-pressure elasticity of a natural magnetite crystal
American Mineralogist (July 2004) 89 (7): 1061-1066

Abstract

Variation of the sound velocities, elastic constants, and compressibility of a natural magnetite crystal were determined using gigahertz ultrasonic interferometry and single-crystal X-ray diffraction to 8.7 GPa. At ambient pressure, the elastic constants are (in GPa): c (sub 11) = 260.5(1.0), c (sub 12) = 148.3(3.0), and c (sub 44) = 63.3(1.5). While c (sub 11) and c (sub 12) have similar positive pressure derivatives of 5.14(13) and 5.39(10), respectively, the c44 elastic constant exhibits mode-softening over this pressure range, with dc (sub 44) /dP = 0.13(4), calculated from the pressure dependence of the [100] shear velocity. The adiabatic bulk modulus (K (sub 0S) ) is 185.7(3.0) GPa, with KS = 5.1(1), and the shear modulus (G (sub 0) ) is 60.3(3.0) GPa, with G' = -0.1(1). The bulk modulus and its pressure derivative obtained dynamically are consistent with the isothermal equation of state, measured on the same sample by single-crystal X-ray diffraction, yielding K (sub 0T) = 180.0(1.0) and K' (sub T) = 5.2(4). Pressure-induced shear-mode softening in magnetite is most likely related to magnetoelastic coupling and the first-order phase transition to an orthorhombic structure above 21 GPa.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 89
Serial Issue: 7
Title: High-pressure elasticity of a natural magnetite crystal
Affiliation: Geoforschungszentrum Potsdam, Potsdam, Federal Republic of Germany
Pages: 1061-1066
Published: 200407
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 28
Accession Number: 2006-011299
Categories: General geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
Secondary Affiliation: Universitaet Bayreuth, DEU, Federal Republic of Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200604
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