HR: 0800h
AN: MR11A-0901    [Abstracts]
TI: Elastic Properties of Zinc Ferrite and Aluminate Spinels
AU: * Reichmann, H J
EM: hanni@gfz-potsdam.de
AF: Hans J. Reichmann, Geoforschungszentrum Potsdam, Section 4.1, Potsdam, 14473 Germany
AU: Jacobsen, S D
EM: s.jacobsen@gl.ciw.edu
AF: Steven D. Jacobsen, Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC, 20015 United States
AB: Spinels are important ternary oxides of Earth's crust and upper mantle, and silicate spinel (ringwoodite) is the stable high-pressure phase of Mg$_{2}$SiO$_{4}$ in Earth's lower transition zone. The zinc ferrite spinel, franklinite (ZnFe$_{2}$O$_{4}$ ) exhibits ferrimagnetism at room pressure. Here we report the effects of iron-aluminium substitution on the single-crystal elastic properties of the zinc ferrite spinel (franklinite) and zinc aluminate spinel, gahnite (ZnAL$_{2}$O$_{4}$)using gigahertz ultrasonic interferometry. We studied natural franklinite from New Jersey and gahnite from North Carolina with measured cell parameters of 8.4456(6) � and 8.0985(2) �, respectively. The adiabatic bulk modulus K$_{S0}$ (Voigt-Reuss-Hill average) of these two spinels is 179(6) GPa for franklinite and 209(5) GPa for gahnite. The shear modulus of the zinc spinels increases dramatically upon substitution of Al for Fe, with G = 65(3) GPa for franklinite and G = 102(3) GPa gahnite. The elastic moduli of franklinite are comparable to those of the magnetite, which we measured to be K$_{S0}$ = 186(3) GPa and G = 60(3) GPa. In an earlier study, we reported the negative pressure dependence of C$_{44}$ and G for magnetite. High-pressure shear-wave measurements are currently underway with franklinite and gahnite in order to determine whether or not pressure-induced shear-mode softening is common also to the zinc spinels.
DE: 3900 MINERAL PHYSICS
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting