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.

O. Tschauner, C. Ma, A. Lanzirotti, M. Newville, “Riesite, the Ries a Impact New High Structure Pressure Polymorph of TiO2 fromthe Reis Impact Structure”, Minerals, 2020, 10. 78, doi: 10.3390/min10010078

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