The Stability of RbAlSi3O8 Under High Pressure Conditions
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University School of Earth Sciences. Shell Undergraduate Research Experience (SURE) Internships. 2008
Potassium and Rubidium are minor and trace elements of the Earth’s mantle, both of which have long-lived radioactive isotopes. 40K is a significant energy source that contributes to the convection of the mantle and outer core, while 87Rb is a geochemical tracer for long-lived mantle processes. In the Earth’s crust, K and Rb are stored in feldspar, KAlSi3O8, the most abundant mineral in the crust. The mineral host of K and Rb in the mantle is uncertain, with implications on reactivity of alkali metals with the Earth’s core. Sample preparation consisted of compressing RbAlSi3O8, Rubidium microcline (rubicline), under pressures of ~15 GPa (gigapascals) in a laser-heated diamond anvil cell (LHDAC). Synchrotron-based x-ray diffraction gives the structure and density at high pressures. The high-pressure structure of Rubidium microcline is similar to that of the high-pressure structure of feldspar, transforming to the hollandite structure at ~15 GPa, then to the hollandite II structure at ~25 GPa. Preliminary results yield the bulk modulus of Rubidium hollandite to be 210 (±10) GPa.
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