In order to elucidate partition behavior of divalent cations between minerals and aqueous chloride solutions under supercritical conditions of fluid phase, we conducted experiments of the simultaneous partitioning of Ni²⁺, Mg²⁺, Co²⁺, Zn²⁺, Fe²⁺, and Mn²⁺ between löllingite (FeAs₂) or safflorite (CoAs₂) and 2 mol/L aqueous chloride solutions under the conditions of 500 and 600 °C, 100 MPa. Natural löllingite and safflorite were used as starting materials. The bulk partition coefficient (K_PB) for the cation partition reactions can be expressed as follows:

where x_MeAs2 indicates the molar fraction of each end–member in the solid phase. m_Meaq is the total molar concentration of Me–bearing aqueous species in aqueous chloride solution. For the experiments using löllingite, the order of partition coefficients of divalent cations was:

 Co²⁺ > Fe²⁺ > Ni²⁺ >> Mg²⁺ = Zn²⁺ ≥ Mn²⁺,

ranging from −4 to 2.3 in logarithm. The order of partition coefficients for safflorite was:

 Co²⁺ > Ni²⁺ >> Fe²⁺ > Mg²⁺ > Zn²⁺ ≥ Mn²⁺,

ranging from −6 to 0.6 in logarithm. The partition coefficient–ionic radius (PC–IR) curves of löllingite and safflorite showed almost no difference between 500 and 600 °C. The PC–IR curves of löllingite and safflorite have a steeper slope than multiple oxide minerals. Mg²⁺, Co²⁺, Fe²⁺, and Mn²⁺ exhibit partition behavior according to ionic radius. On the other hand, Ni²⁺ shows a positive partition anomaly in both löllingite and safflorite, whereas Zn²⁺ shows a large negative partition anomaly that increases with increasing As concentration in the order of pyrite < arsenopyrite < löllingite. Minerals with high ionic bond properties (e.g., ilmenite, magnetite) that have the same 6–fold coordinated sites have a wider PC–IR curve than sulfide, arsenic sulfide, and arsenide minerals with high covalent bond properties. This observation suggests that the selectivity of cations is strong in sulfide, arsenic sulfide, and arsenide minerals with covalent bonds compared with that of multiple oxide minerals with ionic bonds. However, because the electronegativity of arsenic is slightly smaller than that of sulfur, the width of the PC–IR curve seems to slightly narrow in the order of sulfide minerals (pyrite) > arsenic sulfide minerals (arsenopyrite) > arsenide minerals (löllingite).

The Nishiyama volcano is a Quaternary stratovolcano consisting of the northwestern part of the Hachijo–jima island, located in a volcanic front of the Izu–Bonin arc. The Holocene activity of the Nishiyama volcano began at ~ 10–13 ka and has mainly produced basaltic lava flows and scoria fall deposits. While gabbroic and doleritic enclaves are generally found in scoriaceous pyroclasts, we discovered anorthositic enclaves in the lava flows. Here, we report the petrographical and petrological characteristics of the anorthositic enclaves. In the basaltic lava flows, the amount of plagioclase phenocrysts positively correlated with the whole–rock content of Al₂O₃, CaO, and Sr with these elements preferentially contained in the feldspar. In addition, an ideal anorthite content obtained from the whole–rock chemistry of the basaltic lava flows (An₈₈) was largely consistent with the measured anorthite content obtained from anorthosite (An₈₄). These results suggest that the plagioclase fractionation and/or accumulation controls the whole–rock chemical composition of basaltic lava flows and that the accumulated plagioclases represent part of anorthositic enclaves. Anorthosite was divided into three types of textures: 1) Comb texture, 2) adcumulate texture, and 3) radial texture. These textures (from the comb texture to the radial texture) reflected the change in the undercooling state of the magma. Based on the petrography of the anorthosite and lava flows, the plagioclase was in a liquidus phase in the Nishiyama basaltic magma. Additionally, the anorthosite was formed by the effects of adiabatic ascent and the degassing of near–H₂O–saturated magma at the shallow magma reservoir (~ 5 km in depth) beneath the Nishiyama volcano.

The crystal chemistry of Sr–rich piemontite from a layered manganese ore deposit of the Tone mine, Nishisonogi Peninsula, Japan, was studied using methods of electron microprobe analysis, single crystal X–ray structural refinement, ⁵⁷Fe Mössbauer spectroscopy, and X–ray and Time–of–Flight neutron Rietveld analyses to elucidate the intracrystalline distributions of Sr, Mn, and Fe and the general and individual features on the structural changes with Sr contents in piemontite and epidotes. Piemontite in the most piemontite–dominant layer of an ore is [Ca_1.73(15)Sr_0.22(13)]_Σ1.95[Al_1.99(9)Mn³⁺_0.68(8)Fe³⁺_0.37(8)Mg_0.01(0)]_Σ3.05
Si_2.99(1)O₁₂(OH) (Z = 2) in the average chemical formula. A single crystal X–ray structural refinement (R₁ = 2.51% for 2417 unique reflections) resulted in the unit–cell parameters of a = 8.8942(1), b = 5.6540(1), c = 10.1928(2) Å, and β = 115.100(1)°; and the occupancies of Ca_0.711(3)Sr_0.289, Al_0.898(4)(Mn + Fe)_0.102, and (Mn + Fe)_0.949(4)Al_0.051 at the ^XA2, ^VIM 1, and ^VIM 3 sites, respectively. All Fe in a powdered piemontite sample was Fe³⁺ as indicated by the two Mössbauer doublets (isomer shift = 0.351 and 0.367 mm/s and quadrupole splitting = 2.189 and 1.93 mm/s, respectively) assigned to Fe³⁺ at the M 3 site. The neutron Rietveld refinement of the powder sample (R_wp = 2.11%; R_e = 0.88%) resulted in the occupancies of ^{M 1}[Al_0.902(5)Mn_0.098] and ^{M 3}[Mn_0.534(5)Fe_0.267Al_0.20], where ^{M 3}Al was fixed to 0.20Al obtained by X–ray Rietveld refinement (R_wp = 2.95%; R_e = 2.13%). By applying the oxidation state of Fe and the distributions of Al, Fe, and Mn in the M 1 and M 3 sites in the powder sample, the site occupancies in the piemontite single crystal are constructed as ^A2[Ca_0.711(3)Sr_0.289], ^{M 1}[Al_0.898(4)Mn³⁺_0.102] and ^{M 3}[Mn³⁺_0.633Fe³⁺_0.316Al_0.051]. The A2–O7, –O2’, and –O10 distances, 2.303(2), 2.562(1), and 2.592(2) Å, respectively, are longer than those of Ca–piemontites. The mean <M 3–O> and <M 1–O> distances, 2.050 and 1.923 Å, respectively, are close to the published data of Ca–piemontites and Sr–rich and –bearing piemontites with Mn³⁺ + Fe³⁺ contents in the M 3 and M 1 sites similar to those of the Tone piemontite.

A focused ion beam (FIB) scanning electron microscope (SEM) equipped with a low–energy Ar–ion gun, an electron back–scattered diffraction (EBSD) detector, and an energy dispersive spectrometer (EDS) was newly developed for microfabrication, followed by submicroscopic chemical and crystallographic analyses in an identical sample chamber. The surface condition of mineral samples requires extreme care during FIB milling process, especially for EBSD measurement, as the EBSD pattern is greatly affected by a damaged amorphous surface caused by a high–energy Ga–ion beam (30 keV), even when this damaged layer is only tens of nanometers in thickness. Low–energy broad Ar–ion beam milling (1 keV) overcomes this problem and allows us to obtain sharp EBSD patterns. We applied the microfabrication–analysis protocol to a cosmic spherule. Comprehensive mineralogical datasets from SEM images, X–ray elemental maps, and EBSD patterns were successfully obtained from a minute mineral sample, where conventional cutting and polishing processes are not possible.

The Suo metamorphic complex in the Chugoku Mountains of southwest (SW) Japan represents Jurassic high pressure (P )/temperature (T ) type metamorphic rocks. Its high–grade part is exposed in the Nichinan area, where barroisite–bearing mafic schist occurs as ~ 50–m thick layers in pelitic schist. These mafic layers contain the common matrix assemblage barroisite + epidote + albite + quartz + titanite + phengite. Relic minerals (garnet, glaucophane, aegirine–augite, Si–rich phengite and rutile) of early–stage parageneses are preserved within albite porphyroblasts. The textural relations combined with pseudosection modeling suggest a clockwise P –T trajectory from epidote–blueschist facies through the garnet + clinopyroxene stable conditions to epidote–amphibolite facies. Two distinct phases of high–strain ductile deformation (D1 and D2) can be recognized in the area, and they are related to early and late stages of exhumation. Albite porphyroblasts initially grew statically between D1 and D2 at ~ 520–530 °C and ~ 0.8 GPa, and further retrogressive growth of albite rims and chlorite at the expense of barroisite is synchronous with D2. The lithological association, deformation structures and metamorphic conditions of the Jurassic Suo metamorphic complex are very similar to those of the Cretaceous Sanbagawa metamorphic complex, suggesting they have comparable exhumation processes as coherent–type high–P/T metamorphic complexes.