[S-MP36] 鉱物の物理化学

[SMP36-P10] Twinning in wadsleyite

宮島 延吉¹、Johannes Buchen^1,2、*川添 貴章^1,3 (1.バイロイト大学バイエルン地球科学研究所、2.カリフォルニア工科大学地質学惑星科学科、3.広島大学大学院理学研究科地球惑星システム学専攻)

キーワード：マントル遷移層、ウォズリアイト、双晶形成、双晶、双晶面、高圧

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.