HR: 0800h
AN: MR31A-0125    [Abstracts]
TI: High Pressure Study of K-Na Hollandite Solid Solution
AU: * Liu, J
EM: jun.liu@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universit„t Bayreuth, D-95440 Bayreuth, Germany, Bayreuth, 95440 Germany
AU: Boffa-Ballaran, T
EM: Tiziana.Boffa-Ballaran@Uni-Bayreuth.DE
AF: Bayerisches Geoinstitut, Universit„t Bayreuth, D-95440 Bayreuth, Germany, Bayreuth, 95440 Germany
AU: Dubrovinsky, L
EM: Leonid.Dubrovinsky@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universit„t Bayreuth, D-95440 Bayreuth, Germany, Bayreuth, 95440 Germany
AU: Frost, D
EM: Dan.Frost@Uni-Bayreuth.DE
AF: Bayerisches Geoinstitut, Universit„t Bayreuth, D-95440 Bayreuth, Germany, Bayreuth, 95440 Germany
AB: (Na, K)AlSi₃O₈ aluminosilicates hollandite-type materials with their dense structure, in which all Si and Al are in six-fold coordination, are considered as a possible repository of potassium and sodium in the Earth's lower mantle. Phase relations in the system KAlSi₃O₈ - NaAlSi₃O₈ have been examined by other workers at pressures of 5 - 23 GPa and temperatures of 700 - 1200°C, indicating that the maximum solubility of NaAlSi₃O₈ component into KAlSi₃O₈ hollandite-type structure at 1000°C is about 40 mol%. At higher Na content the high pressure phase appears to be that of the calcium-ferrite type structure. However, in the last few years there have been a number of reports of natural occurrences of NaAlSi₃O₈ hollandite in shock-induced melt veins of chondrite. Aim of our research is, therefore, to extent the study of the phase relation of the K-Na system at higher temperature and to determine the physical-chemical properties and high-pressure behaviour of silicate hollandite-type structures containing K and Na in different concentrations. A series of synthesis experiments has been done with the multi-anvil presses at the Bayerisches Geoinstitut in the pressure range 13-25 GPa and 1700°C, using K_xNa_1-xAlSi₃O₈ (x = 1, 0.7, 0.5, 0.4) glasses as the starting materials. X-ray powder diffraction analysis and electron microprobe measurements of the run products show that at 20GPa, pure K_0.7Na_0.3AlSi₃O₈ hollandite has been synthesized, with the lattice parameters of a = 9.3133 (5) Å, c = 2.7226 (2) Å, V = 236.15 (2) ų. At 22 GPa, pure K_0.5Na_0.5AlSi₃O₈ hollandite has been synthesized, with the lattice parameters of a = 9.2984 (4) Å, c = 2.71920 (17) Å, V = 235.103 (15) ų. The pressure stability field of K_xNa_1-xAlSi₃O₈ hollandite appears therefore larger than in the study of privious work. High-pressure X-ray powder and single-crystal diffraction and Raman spectroscopy experiments for this composition are in progress. Preliminary experiments using a NaAlSi₃O₈ end-member glass yield no hollandite-type structure at 22.5GPa and 1700°C. Further synthesis experiments are planned to determine the experimental P-T stability field of NaAlSi₃O₈ hollandite.
DE: 3630 Experimental mineralogy and petrology
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005