[S-MP36] Physics and Chemistry of Minerals

[SMP36-P10] Twinning in wadsleyite

Nobuyoshi Miyajima¹, Johannes Buchen^1,2, *Takaaki Kawazoe^1,3 (1.Bayerisches Geoinstitut, University of Bayreuth, 2.Division of Geological and Planetary Sciences, California Institute of Technology, 3.Department of Earth and Planetary Systems Science, Hiroshima University)

Keywords:mantle transition zone, wadsleyite, twinning, twin, twin boundary, high pressure

Twinning was discovered in wadsleyite, which is the most abundant mineral at the upper part of the mantle transition zone. Wadsleyite crystals were synthesized from a powder of San Carlos olivine with distilled water at a pressure of 15 GPa and a temperature of 1670 K for 3 h using a multi-anvil apparatus. The wadsleyite twin was found based on change in color at a twin boundary due to strong pleochroism of wadsleyite by observing a thin section of the twin by optical microscopy. A thin foil perpendicular to the twin boundary was cut by focused iron beam (FIB) and was observed by transmission electron microscopy (TEM). The TEM observation revealed that twin domains make a 180° rotation about an axis perpendicular to the {101} plane in the pseudo-cubic system (cf. ringwoodite). Moreover, the composition plane of the twin domains is the {101} plane in the pseudo-cubic system. The wadsleyite twinning may be important in phase transformation, growth and deformation.