Sakura quartz, which shows cherry blossom-like texture on the (0001) cross-section, occurs from Obira mine in Oita prefecture, Japan. The unique texture was analyzed by using CL, EBSD, EPMA, BSE, and OPM. The texture includes numerous solid and liquid inclusions, and is composed of Brazil twin lamellae and Dauphine twin domains. The texture would be named as sakura texture after sakura-ishi (cerasite), which was a variety of cordierite. The quartz crystal with the sakura texture grew by two growth stages. At the first stage, numerous inclusions were incorporated into the milky part and the growth bands are indistinct. In contrast, growth bands were clearly observed at the second stage. The sakura texture developed at the first stage. Almost all quartz crystals from Obira mine have the sakura texture, and the texture formed on replacement process at late greisenization. The sakura texture is a characteristic feature of quartz from skarn deposit.

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The experiments on the simultaneous partitioning of divalent cations (Ni²⁺, Mg²⁺, Co²⁺, Zn²⁺, Fe²⁺, and Mn²⁺) between pyrite or pyrrhotite and 2M aqueous chloride solution were conducted under supercritical hydrothermal conditions of 500, 600, 700, and 800 °C, and 1 kb, using standard cold seal type pressure vessels.

 The experimental results revealed that the cations are preferentially partitioned into pyrite and pyrrhotite in the following orders, respectively:

 Co²⁺=Ni²⁺=Fe²⁺>Zn²⁺>Mg²⁺=Mn²⁺ for pyrite

and

 Co²⁺>Ni²⁺≥Fe²⁺>Zn²⁺>Mg²⁺=Mn²⁺ for pyrrhotite.

 If we assume that Mg²⁺ shows a partition behavior according to the ionic radius, the partition coefficient vs. ionic radius (PC-IR) curves for both pyrite and pyrrhotite mark a peak at 0.77 Å. Zn²⁺ shows a negative deviation from the PC-IR curves, but Ni²⁺ shows a positive deviation.

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New phase diagrams in Mg₂Si₂O₆-CaMgSi₂O₆ system and Mg₂Si₂O₆-Fe₂Si₂O₆ system and stability field of high-temperature orthopyroxene in these systems are proposed.
 The enthalpy and volume change of the phase transition between low- and high-temperature orthopyroxenes with composition (Ca_0.06Mg_1.94)Si₂O₆ at atmospheric pressure were obtained to be 6.2 kJ/mol and 10.25 ų/unit cell, respectively, and the slope was calculated to be 0.0056 GPa/°C at transition temperature, 1170 °C. From these values, the phase boundary of these phases was defined as P(GPa) = 0.0056T(°C)-6.55. Using this relationships and data of synthetic experiments in previous studies, the phase diagrams and the stability fields of high-temperature orthopyroxene in Mg₂Si₂O₆-CaMgSi₂O₆ system from atmospheric pressure to 1.0 GPa were determined.
 The transitions between low- and high-temperature orthopyroxenes with the compositions in Mg₂Si₂O₆-Fe₂Si₂O₆ system were observed at about 1000-1200 °C by using high-temperature in-situ X-ray powder diffraction experiments with a multiple-detector system and a high-temperature strip heater chamber in an atmosphere of Ar plus 1% H₂. The stability field of high-temperature orthopyroxene was above 1200 °C and new phase diagram in Mg₂Si₂O₆-CaMgSi₂O₆ system at atmospheric pressure was proposed.

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「宝石と鉱物の大図鑑─地球が生んだ自然の宝物」

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鉱物科学若手の会（YMO）2017年春季会合の報告

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2016年年会記事
2016年年会研究発表優秀賞受賞者渡航支援制度成果報告
一般社団法人日本鉱物科学会平成28年度第1回定例理事会議事録
平成28年12月26日理事会（決議の省略による）議事録

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一般社団法人日本鉱物科学会　定款　その他規約

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