• journal_title：American Mineralogist
• Contributor：Xiuling Wu ; Dawei Meng ; Yujing Han
• Publisher：Mineralogical Society of America
• Date：2005-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2005.1901
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：90
• issue：8-9
• firstpage：1458
• section：Letters

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.