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Elasticity of franklinite and trends for transition-metal oxide spinels

Hans J. Reichmann, Steven D. Jacobsen and Tiziana Boffa Ballaran
Elasticity of franklinite and trends for transition-metal oxide spinels
American Mineralogist (April 2013) 98 (4): 601-608


The pressure dependence of single-crystal elastic moduli of a natural Mn-rich franklinite, (Mn (sub 0.40) Fe (super 2+) (sub 0.16) Zn (sub 0.37) Mg (sub 0.03) )(Fe (super 3+) (sub 1.94) Al (sub 0.08) )O (sub 4) , has been determined by GHz-ultrasonic interferometry in a diamond-anvil cell to 9.8 GPa. The room-pressure elastic constants of franklinite are C (sub 11) = 244(3) GPa, C (sub 12) = 142(4) GPa, and C (sub 44) = 77(2) GPa. Linear pressure derivatives of C (sub 11) and C (sub 12) are 4.3(3) and 3.8(3), respectively, whereas the C (sub 44) modulus exhibits softening, fitted in the P < or = 10 GPa pressure range to C (sub 44) = 77(2) + 0.29(2)P - 0.018(2)P (super 2) GPa. The average of Hashin-Shtrikman bounds on the adiabatic bulk modulus (K (sub S0) ) of franklinite is 175(3) GPa, with pressure derivative K (sub S) ' = 4.3(3), and the shear modulus G (sub 0) = 66(2) GPa with G' = 0.09(3). The isothermal compressibility of franklinite was determined from a separate high-pressure, single-crystal X-ray diffraction experiment to 7.8 GPa, yielding K (sub T0) = 173.5(7) GPa fitted with a fixed pressure derivative of K (sub T) ' = 4. When K' is fixed to the ultrasonic value of 4.3, we obtain K (sub T0) = 172.2(7) GPa. In contrast to iron-free gahnite (ZnAl (sub 2) O (sub 4) ), franklinite exhibits pressure-induced mode softening of C (sub 44) similar to magnetite (Fe (sub 3) O (sub 4) ). Between end-member compositions ZnFe (sub 2) O (sub 4) (franklinite) and MnFe (sub 2) O (sub 4) (jacobsite), the bulk modulus decreases linearly with increasing %Mn, however we observe non-linear behavior in other elastic moduli, especially C (sub 44) , which displays a pronounced negative anomaly for the mid-range Mn composition. Applying Birch's law to AB (sub 2) O (sub 4) -type spinels reveals that oxide spinels containing transition metals on both A and B sites follow a distinct trend from other spinels.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 98
Serial Issue: 4
Title: Elasticity of franklinite and trends for transition-metal oxide spinels
Affiliation: German Research Centre for Geosciences, Helmholtz Centre Potsdam, Potsdam, Germany
Pages: 601-608
Published: 201304
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 46
Accession Number: 2013-036652
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
Secondary Affiliation: Northwestern University, USA, United StatesUniversitaet Bayreuth, DEU, Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201323
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