Mathematics – Logic
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p21b0529r&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P21B-0529
Mathematics
Logic
3620 Crystal Chemistry, 3919 Equations Of State, 3924 High-Pressure Behavior, 3954 X Ray, Neutron, And Electron Spectroscopy And Diffraction
Scientific paper
The monoclinic mineral titanite is a common accessory in many acid and intermediate igneous rock, gneises, mica shists and amphiboles. The structure of titanite is characterized by corner-linked chains of TiO6 -octahedra parallel to [100] connected via isolated SiO4 -tetrahedra. CaO7 polyhedra build chains along [101]. The octahedral Ti atoms show typical out-of-center distortions. Its behavior under high pressure can give information about the driving forces of the phase transition in ABOCO4 silicates. The behavior of titanite under high pressure has been studied up to 7 GPa and 850oK with powder diffraction, respectively [1], [2], [3] and several phase transitions were found. The structure remains monoclinic but changes from P21/a to A2/a at 3.6 GPa. Here we present evidence for a new A2/a P-1 phase transition at 10.5 GPa. At this pressure the cell metric decreased to the following values: a= 6.829(4) Å , b= 8.594(2) Å , c= 6.352(1) Å, α = 90.18(2)° , β = 112.78(2)° , γ = 89.70(2)° and V= 343.7(2) Å3. Structure refinement results of high-pressure X-ray single crystal studies at pressures from 7 to 10 GPa will be presented. In addition, we compare the titanite results to the phase transition in the topological identical malayaite CaSnSiO_4 at 5 GPa, where a similar phase transition has previously been observed [4]. [1] Angel, R.J.; Kunz, M.; Miletich, R.; Woodland, A.B.; Koch, M. and Xirouchakis, D. (1999); High-pressure phase transition in CaTiOSiO_4 titanite; Phase Transitions, 68, 533 - 543 [2] Bismayer, U.; Zhang, M.; Groat, L.A.; Salje, E.K.H and Meyer, H.-W. (1999); The \beta - \gamma Phase Transition in Titanite and the Isosymmetric Analogue in Malayaite; Phase Transitions, 68, 545 - 556 [3] Kunz, M., Arlt, T. and Stolz, J. (2000): In situ powder diffraction of titanite (CaTiSiO_4) at high pressure and high temperature, American Mineralogist, 85, 1465 - 1473 [4] Rath, St, Kunz, M. and Miletich, R. (2001) Pressure induced phase transition in malayaite CaSnOSiO_4$. in preparation
Kunz Martin
Miletich Ronald
Rath Satchidananda
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