A <1 mm fragment recovered from chromitite in the Luobusa ophiolite is composed of a “patchwork quilt” of Ti-Fe intermetallics (Figure) surrounded by an α-Ti rim. Amorphous silicate, kyanite, and coesite pseudomorphs of stishovite constitute a partial outer rim containing osbornite and qingsongite (Yang et al. 2007; Dobrzhinetskaya et al. 2014). The “patchwork quilt” comprises zoned grains surrounded by a vermicular symplectite. Lamellae extracted by FIB and analyzed by TEM and 3D electron diffraction allowed the identification of two distinct Ti-Fe intermetallic phases. Hexagonal Ti10Fe3 is characterized by a κ-phase structure (Hårsta & Rundqvist 1987), with 26 atoms in the unit cell and space group P63/ mmc (#194). Cubic Ti2Fe gives instead the structure of an η-phase (Lavrentyev et al. 2010), with 96 atoms in the unit cell and space group Fd-3 m (#227). Both phases have partially occupied interstitial sites that could contain C, N, O or Si. Our results demonstrate the remarkable capability of 3D electron diffraction in solving and refining the structure of single crystals smaller than 1 μm, paving a way for characterizing new minerals at a completely novel scale (Xiong et al. 2020; Xiong et al. 2022; Xiong et al. 2022).
η-phase Ti2Fe and κ-phase Ti10Fe3: 3D ED study of potential new minerals from Tibet, China
Mugnaioli E.
;
2022-01-01
Abstract
A <1 mm fragment recovered from chromitite in the Luobusa ophiolite is composed of a “patchwork quilt” of Ti-Fe intermetallics (Figure) surrounded by an α-Ti rim. Amorphous silicate, kyanite, and coesite pseudomorphs of stishovite constitute a partial outer rim containing osbornite and qingsongite (Yang et al. 2007; Dobrzhinetskaya et al. 2014). The “patchwork quilt” comprises zoned grains surrounded by a vermicular symplectite. Lamellae extracted by FIB and analyzed by TEM and 3D electron diffraction allowed the identification of two distinct Ti-Fe intermetallic phases. Hexagonal Ti10Fe3 is characterized by a κ-phase structure (Hårsta & Rundqvist 1987), with 26 atoms in the unit cell and space group P63/ mmc (#194). Cubic Ti2Fe gives instead the structure of an η-phase (Lavrentyev et al. 2010), with 96 atoms in the unit cell and space group Fd-3 m (#227). Both phases have partially occupied interstitial sites that could contain C, N, O or Si. Our results demonstrate the remarkable capability of 3D electron diffraction in solving and refining the structure of single crystals smaller than 1 μm, paving a way for characterizing new minerals at a completely novel scale (Xiong et al. 2020; Xiong et al. 2022; Xiong et al. 2022).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
