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Full-Text Articles in Mineral Physics
Zagamiite, Caal2si3.5o11, The Hexagonal High-Pressure Cas Phase With Dominant Si, As A Mineral From Mars, Chi Ma, Oliver Tschauner, John R. Beckett, Eran Greenberg, Vitali B. Prakapenka
Zagamiite, Caal2si3.5o11, The Hexagonal High-Pressure Cas Phase With Dominant Si, As A Mineral From Mars, Chi Ma, Oliver Tschauner, John R. Beckett, Eran Greenberg, Vitali B. Prakapenka
Geoscience Faculty Research
Within the Ca-Al-silicate system, dense, layered hexagonal phases occur at high temperatures and pressures between 20 and 23 GPa. They have been observed both in nature and in experiments. In this study, we describe the endmember with a dominant sixfold coordinated Si as a mineral zagamiite (IMA 2015-022a). This new mineral identified in Martian meteorites has a general formula of (Ca,Na)(Al,Fe,Mg)2(Si,Al,□)4O11, thus defining CaAl2Si3.5O11 as a previously unknown endmember of the hexagonal CAS phases. Zagamiite assumes space group P63/mmc with a unit cell of a = 5.403(2) Å, c = 12.77(3) Å, V = 322.9(11) Å3, and Z = 2. …
Structure Analysis Of Natural Wangdaodeite—Linbo3-Type Fetio3, Oliver Tschauner, Chi Ma, Matthew G. Newville, Antonio Lanzirotti
Structure Analysis Of Natural Wangdaodeite—Linbo3-Type Fetio3, Oliver Tschauner, Chi Ma, Matthew G. Newville, Antonio Lanzirotti
Geoscience Faculty Research
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This paper reports the first structure refinement of natural wangdaodeite, LiNbO3-type FeTiO3 from the Ries impact structure. Wangdaodeite occurs together with recrystallized ilmenite clasts in shock melt veins which have experienced peak shock pressures of between 17 and 22 GPa. Comparison of natural and synthetic wangdaodeite points toward a correlation between the distortion of ferrate-and titanate-polyhedra and the c/a ratio of the unit cell. The Raman spectrum of wangdaodeite is calculated based on the refined structure. Comparison to the reported spectrum of the type-material shows that the Raman peak at 738–740 …
Riesite, A New High Pressure Polymorph Of Tio2 From The Ries Impact Structure, Tschauner, Chi Ma, Antonio Lanzirotti, Matthew G. Newville
Riesite, A New High Pressure Polymorph Of Tio2 From The Ries Impact Structure, Tschauner, Chi Ma, Antonio Lanzirotti, Matthew G. Newville
Geoscience Faculty Research
This paper describes riesite, a new high-pressure polymorph of TiO2 from the Ries impact structure, Germany. Riesite occurs in shock-induced melt veins within xenoliths of bedrock in suevite. It is structurally closely related to srilankite from which it differs by having two distinct cation sites rather than one and through its monoclinic symmetry. It is indicative that riesite forms only upon release from the shock state upon back transformation from akaogiite.