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.
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
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.
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 (Ca0.06Mg1.94)Si2O6 at atmospheric pressure were obtained to be 6.2 kJ/mol and 10.25 Å3/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.