Carbon dioxide (CO₂) is a prevalent volatile in Earth’s interior, but its effects on the structural properties of magmas or silicate melts remain insufficiently understood. Previous studies have indicated that the addition of CO₂ can decrease the viscosity of silicate melts, but only if they are fully polymerized. In this study, we explored the effects of CO₂ considering the degree of polymerization on the structure of silicate melts at high pressures of up to ∼ 5 GPa using in situ synchrotron X-ray diffraction (XRD) measurements and classical molecular dynamics (MD) simulations. The first sharp diffraction peak (FSDP) position of the X-ray structural factor S(Q), which shows the periodicity of an intermediate-range structure, was not affected by the addition of CO₂ for partially depolymerized sodium silicate melt (Na₂Si₃O₇). On the other hand, the height of the FSDP for fully polymerized silica melt (SiO₂) slightly decreased, indicating that the Si-O network structure was disordered by the addition of CO₂. This difference in the behavior of the FSDP may be attributed to the type of carbon species.

Several coarse-grained mafic bodies with evidence for eclogite-facies metamorphism are present in the Besshi area of the Sambagawa subduction-type metamorphic belt, SW Japan. Among them the granulite-bearing Eastern Iratsu metagabbro body involves an unresolved problem of whether it originated in the hanging-wall or footwall side of the subduction zone. The key to settle this problem is its relationship with the adjacent Western Iratsu metabasaltic body, which includes thick marble layer and certainly has the footwall ocean-floor origin. Several previous studies consider that the Western and Eastern Iratsu bodies were originally coherent in the footwall side and formed the shallower and deeper parts of a thick oceanic crust, respectively. The validity of this hypothesis may be assessed by deriving pressure-temperature history of the Eastern Iratsu body, or especially the pressure (depth) condition of the granulite-facies metamorphism before the eclogite-facies overprinting because, if the pressure was relatively high, the oceanic crust assumed in the above hypothesis might be too thick to tectonically achieve the present-day adjacence of the two bodies on the geological map. This study petrologically analyzes a garnet-bearing granulite from the Eastern Iratsu body and newly reports stable coexistence of garnet and orthopyroxene in the sample. By utilizing a garnet-orthopyroxene geothermobarometer, the minimum P-T conditions of the granulite-facies stage was estimated to be 0.8 GPa (∼ 27 km in depth) and 780 °C. If the Western and Eastern Iratsu bodies were assumed to have formed a coherent oceanic crust before their subduction, the original thickness of it was >27 km and this demands unusually strong ductile shortening (<1/9) or unrealistically large vertical displacement on intraplate faulting, suggesting invalidity of the assumption. The Western and Eastern Iratsu bodies, therefore, are originally bounded by subduction-boundary fault and the obtained pressure of 0.8 GPa can be interpreted to represent that of the hanging-wall lower continental crust in the subduction zone, where the Eastern Iratsu body originated. After the granulite-facies metamorphism, the Western Iratsu body, which was located near the footwall surface, initiated subduction and was subsequently juxtaposed with the above-located Eastern Iratsu body at the corresponding depth (∼ 27 km or greater) along the subduction boundary.

Na pyroxene (Napx) of the aegirine-jadeite series occurs as a major metamorphic mineral in metacherts and metabasalts of the lawsonite blueschist (LBS) subfacies in the Kurosegawa belt, Kyushu, Japan. Its jadeite content [X_Jd = ^VIAl/(^VIAl + Fe³⁺ + Ca)] is highly variable at the thin section scale and is crucially influenced by associated minerals, such as albite and sodium amphibole (Namp). Whereas the coexistence with albite and quartz imposes an upper limit on X_Jd in Napx through the equilibrium reaction Ab = Jd + Qz, this paper reveals that uniformly low X_Jd was observed when albite was absent in the metacherts and the coexistence with Namp also effectively reduced X_Jd. In the former case available Na and Al content is limited in metacherts and in the latter case the Al/Fe³⁺ distribution between Napx and Namp controlled the X_Jd in metacherts and metabaslts. Notably, the distribution coefficient [K_D = (Al/Fe³⁺)^Namp/(Al/Fe³⁺)^Napx] systematically varied depending on the mode of growth: K_D ∼ 4 in metabasalts, where Napx developed replacing relict igneous pyroxenes (i.e., topotaxial growth), whereas K_D ∼ 1 in metacherts and metamorphic veins developed in metabasalts, where no relict phase was involved (i.e., nucleation and growth). Previous studies confirmed this trend, suggesting a convergence of K_D to 1 in higher grade rocks, such as epidote-blueschist and eclogite facies. This implies a kinetic control on the distribution process, particularly at lower temperatures (<300 °C). In summary, low-grade Napx associated with igneous pyroxene may represent a metastable state; thus, those in metacherts can serve as a more reliable proxy for the equilibrium conditions of the clinopyroxene system in these grades.

Listvenites and carbonated serpentinites are found in the shear zone of the Median Tectonic Line at the Urayama River, Shikokuchuo City, Ehime Prefecture, Japan. The listvenites are classified into schistose and massive types, and they mainly consist of quartz, magnesite, and dolomite, with minor amounts of Cr-bearing clay minerals. Furthermore, the listvenites contain chromite and small amounts of sulfide minerals, such as millerite and the gersdorffite-cobaltite series. The occurrence of schistose listvenites in the pelitic schist side through the shear zone is a characteristic feature of the listvenites from the Urayama River. The carbonated serpentinites consist of antigorite, magnesite, and quartz, exhibiting a texture in which the lath-shaped antigorite is partially replaced by magnesite. The protoliths of the massive and schistose listvenites are considered to be serpentinite and pelitic schist, respectively, based on their texture, Mg# of magnesite, presence of chromite, and whole-rock chemical compositions. The massive listvenites at the Urayama River are formed from serpentinites that reacted with fluids containing Ca, Sr, K, Na, and CO₂. The fluids that reacted and were released from serpentinites, containing Ca and CO₂, enriched in Mg, Cr, Ni, and Co, likely interacted with the pelitic schist through the shear zone, producing the schistose listvenite.

The northern Lhasa terrane in Tibet is widely developed with Cretaceous magmatic rocks, but their petrogenesis and tectonic setting are still controversial. This study focuses on the Badui pluton in the Luolong area of Tibet and conducts a series of analyses on these granitic rocks, including petrology, geochemistry, and zircon U-Pb geochronology. The Badui pluton mainly consists of biotite monzogranite and diorite porphyry veins with zircon U-Pb ages of 131.7 and 120.1 Ma, respectively, showing that they both formed in the Early Cretaceous. The biotite monzogranite has SiO₂ and total alkali (Na₂O+K₂O) contents of 70.02-71.50 and 6.60-8.06%, respectively, and a Rittmann index (σ) of 1.53-2.40, indicating a metaluminous to weakly peraluminous I-type granite affinity. The diorite porphyry has SiO₂ and total alkali (Na₂O+K₂O) contents of 58.78-60.85 and 5.49-6.57%, respectively. The rare earth and trace element compositions indicate that both the biotite monzogranite and diorite porphyry are enriched in light rare earth elements and large ion lithophile elements, however, depleted in heavy rare earth elements and high field strength elements such as Nb, Ta, and Ti. Together with the previous studies, formation of the Early Cretaceous Badui pluton is a response for the southward subduction of the Bangong-Nujiang Ocean. The diorite porphyry has high Sr, low Y characteristics and more depleted Hf isotopic composition, suggesting that subduction sediments were added during the partial melting of subducted oceanic crust, while the biotite monzogranite has opposite characteristics, suggesting that it was derived from partial melting of ancient lower crustal material.

The crystal structures of clinoclase from Ikuchi-shima, Hiroshima, Japan, Cu₃AsO₄(OH)₃ [monoclinic, space group P2₁/c, with a = 7.2798(3), b = 6.4694(2), c = 12.4172(5) Å; β = 99.5060(10)° V = 576.77(4) ų, R1 = 0.0222 for 1734 independent reflections] and callaghanite from Sierra Magnesite Mine, Nevada, USA, Cu₂Mg₂(CO₃)(OH)₆·2H₂O [monoclinic, space group C2/c, with a = 10.0168(9), b = 11.7671(10), c = 8.2383(6) Å; β = 107.416(6)° V = 926.53(14) ų, R1 = 0.0368 for 1057 independent reflections] were refined using single-crystal X-ray diffraction. In clinoclase, Cu1Cu2(OH)₄O₄ and Cu3₂(OH)₄O₄ dimers share corners to form sheet structures with As tetrahedra. These sheets are held together by long Cu-O bonds [2.524(3) and 2.877(2) Å] and O6-H61…O3 bonds [O6-O3 = 2.852(3) Å]. In callaghanite, tunnel structures are formed within a three-dimensional framework constructed by sharing edges among polyhedra in the zigzag chains of Mg octahedra and the Cu₂(OH)₆·2H₂O units. The hydrogen atoms H31, H61, and H62 are located in the tunnels and the O2 corner of the carbonate ion protrudes into the tunnel. The Cu square bases of tetragonal pyramid in clinoclase are highly distorted with extremely large variations in bond distances. The differences between the shortest and longest bond distances, Δ_distance, in square base are 0.179 Å for Cu1 site, 0.106 Å for Cu2 site, and 0.126 Å for Cu3 site. In callaghanite, the variety of edge sharing manners and chemical species of ligand led to large variations in the Mg-O distances in the octahedron. Δ_distance between the shortest Mg-O distance [2.059(2) Å] and the longest distance [2.123(2) Å] is 0.064 Å, which is larger than that in Cu-O distances in the square base of the Cu tetragonal pyramid (0.037 Å).

The experimentally determined unit cell parameters and atomic coordinates of clinoclase and callaghanite were optimized using first-principles calculations. Three-dimensional representations of covalent and anti-bonding interactions around Cu atoms in both minerals were constructed. The values of bond overlap population in the square bases of clinoclase vary from 0.44 to 0.16, while those in callaghanite show lesser variation, ranging from 0.37 to 0.29. The absolute values of partial orbital-orbital anti-bonding correlations between As and Cu in clinoclase (−0.22 to −0.11) are larger than those between Cu and Cu or Mg in callaghanite (−0.14 to −0.11), indicating the significant influence of As on both antibonding and covalent bonding behaviors in clinoclase. In conclusion, the large dispersion in bond distances within square planar covalent bonds in clinoclase can be attributed to the effects of adjacent highly covalent cations, mediated via oxide ions.

We conducted detrital zircon U-Pb dating and Raman spectral analysis of carbonaceous material (CM) around the Takihara thrust, which is thought to be the boundary between the Sanbagawa metamorphic complex and Chichibu accretionary complex in the central Kii Peninsula, southwest Japan. The Mikabu greenstones, which are normally used to define the boundary, are missing from this area. U-Pb dating of psammitic rocks yields a youngest age of ∼ 118 Ma on the northern side of the Takihara thrust and ∼ 158 Ma on the southern side. The youngest age and age distribution obtained for the sample from the northern side is consistent with data for the Sanbagawa metamorphic complex in other regions, and the age data obtained for the sample from the southern side are consistent with the Chichibu accretionary complex, demonstrating that the Takihara thrust is the geological boundary between these complexes. We examined two parameters of the Raman spectra from CM: the temperature estimated from the full width at half maximum of the D1 band (T_D1) and the ratio of the intensities of the D4 and D1 bands (D4/D1_int). We obtained T_D1 values of ∼ 275-290 °C on the northern side of the Takihara thrust and ∼ 275-280 °C on the southern side, with no clear difference across the thrust. In contrast, there is a clear difference in D4/D1_int values across the thrust: ∼ 0.30-0.33 on the northern side and ∼ 0.47-0.50 on the southern side. This suggests that the D4/D1_int value can not only be used to distinguish between the Sanbagawa and Chichibu complexes in the central Kii Peninsula, but it is also useful for detecting differences in metamorphic grade in low-grade metamorphosed rocks that cannot be detected by the geothermometer that uses the full width at half maximum of the D1 band.

Single phase of Na-bearing grace titanosilicate (Na-GTS) powder was prepared hydrothermally. Its Cs⁺-exchanged forms [Na_4(1−x)Cs_4xTi₄O₄(SiO₄)₃·nH₂O] with various compositions up to x = 1.0 were produced by shaking the Na-GTS in the CsCl aqueous solutions with the Cs-concentration (C_Cs) up to 1.0 mol/L at temperatures up to 80 °C for 24 h. The Cs⁺-exchange rates (x) at each temperature increase steeply with increasing C_Cs up to 0.1 mol/L, after which they are almost constant. Meanwhile, up to 60 °C the x values do not depend significantly on treatment temperature, but at a higher temperature of 80 °C they increase dramatically up to unity. Thus, at least above 80 °C, the increase in treatment temperature is considerably effective for promotion of ion-exchange, as well as the increase in C_Cs. TG-DTA measurements show that the exchange of Na⁺ ions for Cs⁺ ions largely decreases H₂O contents, as a consequence of a remarkable reduction in available void-space within the cavities due to a remarkable increase in mean cation size. The comparison between the observed XRD pattern and the simulated ones suggests the cation-distribution model that Cs⁺ ions prefer the 6g site in the GTS cavity in the assumed pseudocubic structure to the 4e site. The unit cell volumes increase largely with increasing x although the H₂O contents reduce largely. This can be because moderate bonding forces acting between a Cs⁺ ion on the 6g site, located at the proximity of the centers of the 8-membered ring windows, and adjacent O atoms forming the windows directly influence the framework structure. Furthermore, these findings are compared with those of the previously reported Er³⁺-exchanged forms, in terms of the difference in valence and size of the extra-framework cations.

The environmental problems caused by CO₂ emissions endanger human lives. Under these circumstances, carbon dioxide capture, utilization, and storage (CCUS) is likely to reduce CO₂ gas emissions with economic advantages. An application of CCUS is the reinforcement of mechanically weak bio-based composite plastics. Needle-like calcium carbonate crystals can potentially reinforce weak plastics. Moreover, the synthesis of calcium carbonate via carbonation can reduce CO₂ emissions. Here, we review the development of synthetic methods for needle-like aragonite (which is a polymorph of calcium carbonate crystals) using a gaseous CO₂ for further development of efficient synthetic conditions and precise control of morphology. Various factors influencing the synthesis of aragonite have been discussed. These include the temperature; degree of supersaturation of CaCO₃; pH; additives; and external stimuli such as high gravity, sound waves, and microbubbles. The estimated elastic moduli of aragonite were anisotropic depending on the crystal direction. This indicated the importance of controlling the long-axis direction of aragonite as a novel reinforcement material.

We report an outcrop of tonalitic mylonite along the Median Tectonic Line (MTL) in the Ryoke Belt near Sakurabuchi Park in Shinshiro City, Aichi Prefecture. The mylonite has a foliated porphyroclastic texture with coarse (up to a few millimeters) feldspar grains in a greenish/brownish matrix. The strike of the foliation is approximately parallel to that of the MTL. The mylonite consists of plagioclase (locally K-feldspar) porphyroclasts in a fine-grained foliated matrix that consists mainly of dynamically recrystallized quartz aggregates, along with plagioclase and biotite/chlorite. The feldspar porphyroclasts contain quartz-filled fractures and have a asymmetric shape that indicates dextral shear. The quartz c-axis fabric has an intense Y-maxima with a weak cross-girdle pattern. These features of the mylonite fabric are similar to those of porphyroclastic mylonites, such as the Kashio mylonite, which occur along the MTL in other regions.

Cuprospinel, which is rarely been found in nature, was identified on the Yuhama coast in Aogashima Island, Tokyo, Japan. Cuprospinel occurred as one of the sublimated minerals in a rim of black spherical aggregates with hematite as the core. In one sample, the cuprospinel was found to have a composition of (Cu_0.86Fe²⁺_0.08Mg_0.04Mn_0.02Ca_<0.01)(Fe³⁺_1.98Al_0.01Ti_<0.01)O₄, and exhibited a crystal structure with tetragonal symmetry (I4₁/amd) and unit cell parameters of a = 5.826(2) Å, c = 8.682(5) Å, and V = 294.7(3) ų. Another sample had a composition of (Cu_0.60Mg_0.21Fe²⁺_0.10Mn_0.05Ca_0.03)(Fe³⁺_1.99Al_0.01Ti_<0.01)O₄, and its crystal structure exhibited cubic symmetry (Fd3m) with unit cell parameters of a = 8.358(3) Å and V = 583.7(6) ų. Both samples may have undergone growth at high temperature and subsequent annealing at low temperature, so that the difference in crystal structure may be mainly due to the abundance of Cu²⁺ Jahn-Teller cations. This is the first demonstration of the occurrence of tetragonal cuprospinel in a natural environment.

Bentonite will be exposed to γ radiation during geological disposal of high-level radioactive waste. Montmorillonite is the main mineral component of bentonite, and the study on how γ radiation affects the microstructure can help us comprehend how bentonite works and how it evolves. Montmorillonite extracted from GaoMiaoZi (GMZ) bentonite was irradiated by a ⁶⁰Co source (average energy is 1.25 MeV) with a dose rate of 2.88 kGy·h⁻¹ and absorbed dose of 1.0, 2.0, and 3.0 MGy. The samples were then tested by X-ray diffraction, synchronous thermal analysis, Mössbauer spectroscopy, infrared spectroscopy, Raman spectroscopy, and a Four-bar mass spectrometer. The results showed that: γ radiation reduced the d₀₀₁-value, and the average grain size decreased from 5.6 to 4.5 nm. The partial Si-O bonds of the tetrahedral structure, Al-O bonds of the octahedral structure, and hydroxyl (OH) groups in the montmorillonite structure were destroyed, and the mass loss of the hydroxyl (OH) groups decreased from 2.64 to 2.30%. The unit cell charge of montmorillonite rose as a result of H radicals produced by the radiolysis of water entering the crystal structure and converting Fe³⁺ to Fe²⁺. The content of Fe³⁺ decreased from 91 to 83%, while the content of Fe²⁺ increased from 9 to 17%. γ radiation damaged the partial microstructure of montmorillonite and induced the changes in the valence state of structural ion.