Compositional variation of olivine in serpentinized peridotites provides a significant constraint on modeling the redox conditions of serpentinization and the tectonothermal history of ophiolites. Here I report the variations of Fe, Mg, Mn, and Ni contents of olivine from the Oeyama ophiolite, SW Japan and show textural and chemical evidence for compositional modification of olivine related to high–temperature (T) serpentinization. The Fe–enrichment of olivine adjacent to antigorite without significant magnetite formation indicates a reducing condition for high–T serpentinization. Systematic variations of forsterite (Fo) component with distance from antigorite suggest Mg–Fe volume diffusion took place in olivine porphyroclasts under the conditions of high–T serpentinization. In addition, a similar diffusion pattern of Mn to Fe results in a retrograde trend in MnO–Fo diagram, which could be a useful indicator of high–T serpentinization. Retrograde antigorite is different from prograde antigorite in having a shape of elongated blade, lacking a significant amount of magnetite inclusion, and being more ferrous than lizardite. The existence of retrograde antigorite provides another piece of evidence for high–T serpentinization even if olivine has been decomposed by intense low–T serpentinization. Approximate estimation of time required for the observed Mg–Fe diffusion profiles of olivine porphyroclasts reveals that a cooling duration under the conditions of high–T serpentinization was much longer than that of amphibolite–facies metasomatism previously reported. This suggests a long residence time of the forearc peridotites within the serpentinized mantle wedge following rapid exhumation immediately after the amphibolite–facies metasomatism.

The presence of adsorbed ions on calcite surfaces can significantly affect the adsorption and desorption of organic molecules, which is critical for oil recovery and biomineralization. In this study, the structure of calcite–artificial seawater interfaces from 25 to 80 °C was experimentally and theoretically investigated by surface X–ray scattering and molecular dynamics simulations, respectively. The small difference in the CTR scattering profiles at different temperatures could be attributed to the relaxed outermost calcite surface. The electron density profile of the NaCl solution (0.5 mol/kg) exhibits peaks near the calcite surfaces. The two peaks closest to the surface can be interpreted as adsorbed water molecules, inner–sphere Na⁺ complexes, and inner– and outer–sphere Cl⁻ complexes. Thus, the adsorbed Cl⁻ formed two peaks near the calcite’s surface, while Na⁺ formed a single peak as an inner–sphere complex. It should be noted that there was no strong covalent bond between these inner–sphere complexes and the calcite surface. These structural differences between adsorbed cations and anions could be explained by the balance of the interactions between the surface Ca²⁺ and CO₃²⁻, adsorbed ions, and the surrounding water molecules. The presence of inner–sphere Cl⁻ complexes destabilizes surface Ca²⁺, whereas Na⁺ has an insignificant effect on the structure of surface CO₃²⁻. Adding a small amount (0.045 mol/kg) of Mg²⁺ and SO₄²⁻ appears to enhance the relaxation of the interfacial structure.

Kannanite, a new Ca–dominant member of the ardennite series, was obtained from Kannan Mountain, Ozu, Ehime Prefecture, Japan. Kannanite occurs in fine quartz veins crossing the hematite–rich regions of an iron–manganese ore included in the metachert. These veins are pale orange in color, while the kannanite itself is brownish–orange to orange, with a thin section exhibiting weak pleochroism. The mineral was found in grain sizes ranging from several to 15 µm and has a Mohs hardness of 6 and a calculated density of 3.43 g cm⁻³. The mean refractive index obtained from the Gladstone–Dale relationship for this mineral is 1.788. The empirical formula for kannanite is
(Ca_3.60Mn²⁺_0.40)_Σ4(Al_3.00Mn³⁺_1.31Fe³⁺_0.69Mg_0.71Mn²⁺_0.19Ni_0.06Cu_0.05)_Σ6
[(V⁵⁺_0.70Si_0.16As_0.14)_Σ1O_3.84(OH)_0.16](SiO₄)₂(Si₃O₁₀)(OH)₆,
while the simplified formula is Ca₄[(Al,Mn³⁺,Fe³⁺)₅Mg] (VO₄)(SiO₄)₂(Si₃O₁₀)(OH)₆. Kannanite has an orthorhombic structure with a space group Pnmm and unit cell parameters a = 8.8802(14) Å, b = 5.9919(13) Å, c = 18.882(3) Å and V = 1004.7(3) ų. Kannanite is considered to be formed by the activities of metamorphic fluid accompanied with the Sanbagawa metamorphism.

The crystal chemistry of poppiite, V–analogue of pumpellyite–group mineral, from the Komatsu mine, Saitama Prefecture, Japan and from the Gambatesa mine, Genova, Italy (type locality) were studied using electron microprobe (EMPA) and X–ray single–crystal diffraction methods. Both samples are characterized by very high V content, and the average V₂O₃ content is 31.1 wt% for the Komatsu poppiite and 25.4 wt% for the Gambatesa specimen. The Komatsu specimen in this study is the V–richest poppiite ever reported. Structure refinements converged to R₁ values of 5.01% for Komatsu and 3.74% for Gambatesa. The determined structural formula (Z = 4) of poppiite from the Komatsu and Gambatesa mines is
Ca_2.00^X(V³⁺_0.54Fe³⁺_0.01Mg_0.19Mn²⁺_0.22Al_0.04)^Y
(V³⁺_1.73Fe³⁺_0.03Al_0.24)Si_3.00O_10.59(OH)_3.41,
and
Ca_2.00^X(V³⁺_0.49Fe³⁺_0.08Mg_0.19Mn²⁺_0.17Al_0.07)^Y
(V³⁺_1.35Fe³⁺_0.21Al_0.44)Si_3.00O_10.64(OH)_3.36, respectively. Both specimens are classified as poppiite–(V³⁺) because the X and Y octahedral sites are predominantly occupied by V³⁺. The Me²⁺:Me³⁺ ratio at X in this study is 0.41:0.59 for the Komatsu poppiite, and 0.36:0.64 for the Gambatesa one. The former has the larger unit–cell volume (1033.2 ų) than the latter (1026.6 ų). Both charge distribution analysis and located hydrogen sites indicate that O5, O7, O10, and O11 positions host hydroxyl groups. The <Y–O> distance and cell–dimensions positively correlate with mean ionic radius at Y. On the other hand, the a– and c–dimensions are shorter than the values expected by the regression lines estimated by approximately Me²⁺:Me³⁺ ≈ 0.5: 0.5 because of the high proportion of Me³⁺ at X. The studied poppiite crystals are characterized by small β angles [97.283(2)° for Komatsu, and 97.343(3)° for Gambatesa]. These values are considered to be related to distortional variations of the YO₆ octahedra caused by the different characteristics of octahedral V³⁺ ions compared to Fe³⁺ and Cr³⁺.

Recent structural study of the high–pressure Zn₂SiO₄ phases III and IV has suggested that they are retrograde phases formed during decompression. To clarify the stabilities of these phases under pressure, in–situ high–pressure Raman spectroscopic measurements were taken at room temperature. Phase III, having a ‘tetrahedral olivine’ structure, transformed to a new phase at 5.5 GPa during compression and returned to phase III at 1.7 GPa during decompression. Phase IV also exhibited a phase transition at 2.5 GPa with very small hysteresis. Both transitions are first–order. These observations confirmed that phases III and IV are retrograde phases.

To examine the systematic decrease in permeability with crustal age in the uppermost layer of the oceanic crust, we investigated the effect of mechanical compaction on the permeability of basalt cores from Hole 765D and Hole 456 of the Ocean Drilling Program. The results indicate that permeability systematically decreases with increasing confining pressure. However, the pressure effects observed in the laboratory experiments are insufficient to fully explain the result of in–situ measurements of permeability through the oceanic crust. The permeability of core samples is closely related to porosity, both of which reduce with increasing crustal age. We infer that the evolution of permeability of the oceanic upper crust could be controlled by a reduction in porosity due to carbonate mineral precipitation.