α-PbO2-type nanophase of TiO2 from coesite-bearing eclogite in the Dabie Mountains, China

• Published in: The American mineralogist Vol. 90; no. 8-9; pp. 1458 - 1461
• Main Authors: Wu Xiuling, Wu Xiuling, Meng Dawei, Meng Dawei, Han Yujing, Han Yujing
• Format: Journal Article
• Language: English
• Published: Washington Mineralogical Society of America 01.08.2005; Walter de Gruyter GmbH
• Subjects: Asia; cell dimensions; China; coesite; crystal structure; Crystals; Dabie Mountains; eclogite; Far East; framework silicates; Geophysics; high pressure; lead; metals; metamorphic rocks; Metamorphism; mineral properties; Mineralogy; Mountains; Oxidation; oxides; pressure; silica minerals; silicates; Titanium; Titanium dioxide; titanium oxides; Transmission electron microscopy; ultrahigh pressure; unit cell; X-ray data; Dabie Mountains
• ISSN: 0003-004X; 1945-3027
• DOI: 10.2138/am.2005.1901

A natural high-pressure phase of titanium oxide with α-PbO2-structure has been found in omphacite from coesite-bearing eclogite at Shima in the Dabie Mountains, China. High-resolution transmission electron microscope observations have revealed an orthorhombic lattice, corresponding to α-PbO2-type TiO2 with cell parameters a = 0.461 nm, b = 0.540 nm, c = 0.497 nm and space group PBCN: It occurs as nanometer-thick (<2 nm) lamellae between multiple twinned rutile crystals, providing additional evidence of very high-pressure, metamorphism at 7 GPa, 900°C. This implies subduction of continental material to a depth of more than 200 kilometers. α-PbO2-type TiO2 could be an extremely useful index mineral for ultrahigh-pressure.