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Open AccessArticle

High-Pressure and High-Temperature Phase Transitions in Fe2TiO4 and Mg2TiO4 with Implications for Titanomagnetite Inclusions in Superdeep Diamonds

Department of Chemistry, Gakushuin University, Mejiro, Toshima-ku, Tokyo 171-8588, Japan
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Minerals 2019, 9(10), 614; https://doi.org/10.3390/min9100614
Received: 8 September 2019 / Revised: 3 October 2019 / Accepted: 3 October 2019 / Published: 6 October 2019
(This article belongs to the Special Issue Mineral Physics—In Memory of Orson Anderson)
Phase transitions of Mg2TiO4 and Fe2TiO4 were examined up to 28 GPa and 1600 °C using a multianvil apparatus. The quenched samples were examined by powder X-ray diffraction. With increasing pressure at high temperature, spinel-type Mg2TiO4 decomposes into MgO and ilmenite-type MgTiO3 which further transforms to perovskite-type MgTiO3. At ~21 GPa, the assemblage of MgTiO3 perovskite + MgO changes to 2MgO + TiO2 with baddeleyite (or orthorhombic I)-type structure. Fe2TiO4 undergoes transitions similar to Mg2TiO4 with pressure: spinel-type Fe2TiO4 dissociates into FeO and ilmenite-type FeTiO3 which transforms to perovskite-type FeTiO3. Both of MgTiO3 and FeTiO3 perovskites change to LiNbO3-type phases on release of pressure. In Fe2TiO4, however, perovskite-type FeTiO3 and FeO combine into calcium titanate-type Fe2TiO4 at ~15 GPa. The formation of calcium titanate-type Fe2TiO4 at high pressure may be explained by effects of crystal field stabilization and high spin–low spin transition in Fe2+ in the octahedral sites of calcium titanate-type Fe2TiO4. It is inferred from the determined phase relations that some of Fe2TiO4-rich titanomagnetite inclusions in diamonds recently found in São Luiz, Juina, Brazil, may be originally calcium titanate-type Fe2TiO4 at pressure above ~15 GPa in the transition zone or lower mantle and transformed to spinel-type in the upper mantle conditions. View Full-Text
Keywords: phase transition; high pressure; Mg2TiO4; Fe2TiO4; spinel; ilmenite; perovskite; lithium niobate; calcium titanate; diamond inclusion phase transition; high pressure; Mg2TiO4; Fe2TiO4; spinel; ilmenite; perovskite; lithium niobate; calcium titanate; diamond inclusion
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Akaogi, M.; Tajima, T.; Okano, M.; Kojitani, H. High-Pressure and High-Temperature Phase Transitions in Fe2TiO4 and Mg2TiO4 with Implications for Titanomagnetite Inclusions in Superdeep Diamonds. Minerals 2019, 9, 614.

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