Magnesium silicate hydrate (M–S–H) has been considered to play a significant role in different fields of engineering geology including radioactive waste disposal and geological storage of CO₂. However, M–S–H has been discussed only with synthetic samples in most previous studies. To confirm and characterize M–S–H precipitated in natural surface environments, and to assess the formation conditions and processes of the M–S–H, we investigated present-day precipitation of M–S–H at an ultramafic body in the Kamuikotan tectonic belt, Hokkaido, Japan. We collected seepage, surface water, and surface sediments on the ultramafic rock mass. Seepage and surface water showed alkaline pH and Mg²⁺–HCO₃⁻ type water. Although bulk XRD analysis of the sediments did not clearly identify peaks of M–S–H due to its low crystallinity, microscopic observation showed that the sediments contained solid phases that are precipitated interstitially around the detrital serpentine particles. A TEM analysis identified the phases as M–S–H that may be mineralogically considered as a low-crystalline chrysotile with nano-tubular morphology. Thermodynamic calculations for the collected liquid samples suggest that mixed solution of seepage and surface water having high Si activity can induce the formation of M–S–H. The precipitation of M–S–H is likely to be a commonly occurring phenomenon in natural Mg–Si–H₂O systems where geochemical environments contain alkaline fluid that shows high Si activity and meets the thermodynamic conditions for M–S–H formation. In addition to the precipitation of M–S–H in Mg–Si–H₂O systems, we also observed that M–S–H is precipitated even under conditions including Ca and CO₂ species (i.e., Mg–Ca–Si–CO₂–H₂O systems), with a simultaneous precipitation of aragonite. This study supports an understanding of the precipitation of M–S–H by mineral–water interactions in natural surface/subsurface environments for various engineering geology fields.

The crystal structure of a swellable sodium tetra-silicic fluoro-mica [NaLiMg₂Si₄O₁₀F₂], “Na-TN,” was determined and refined by means of XRD data collected with a single crystal in a dry N₂ gas flow. Na-TN is in triclinic space group C1̄, and has unit cell parameters: a=5.2204(10), b=9.0812(17), c=9.652(2) Å, α=91.202(7), β=95.905(7), γ=90.037(7)°, and V=455.06(16) ų. The structural formula, Na_0.874(Mg_0.706Li_0.294)₂(Mg_0.715Li_0.285)Si₄O₁₀F₂, suggests an isomorphous substitution of Li⁺+Na⁺→Mg²⁺+□ forming solid solution series from the ideal composition [NaLiMg₂Si₄O₁₀F₂] toward the dehydrated hectorite composition [Na_0.3(Mg,Li)₃Si₄O₁₀(F,OH)₂·nH₂O]. The lengths of a and b are slightly shorter than those of tainiolite, and intermediate between those of aspidolite and paragonite. At the same time, the interlayer spacing is markedly collapsed. The 6-membered ring of tetrahedra adopts a roughly hexagonal configuration similar to those in tri-octahedral micas. An interlayer Na⁺ ion forms an asymmetrically-coordinated polyhedron with 6+4 basal O on the tetrahedral sheet. It is possibly this irregular coordination which makes the sodium tetra-silicic fluoro-mica swellable.

First, in order to find suitable evaluation factors of zearalenone (ZEA) adsorption ability of clay and treated clay materials, their specific surface area values obtained from nitrogen and water adsorption isotherms, SA_(N2) and SA_(H2O), and monolayer adsorption capacities of water and toluene obtained from each adsorption isotherms, Vm_(H2O) and Vm_(toluene), were measured together with their ZEA adsorption ability. However, any good relationships between the measured values and the ZEA adsorption ability were not recognized here. This result means that the mechanism of ZEA adsorption is complicated depend on the kind of clay. From the water and toluene adsorption isotherms of these adsorbents, the reason of the higher adsorption ability of clays such as magnesium silicate and talc adsorbents was clarified and a certain good relationship between the SA_(H2O)/SA_(N2) ratio and the ZEA adsorption ability was found for these adsorbents. Next, the acid treatment and heat treatment of the Japanese acid earth, JAE sample, were carried out to develop economically the effective adsorbent for ZEA in aqueous solutions. Consequently, the heat treatment of the JAE sample resulted a dramatic decrease in the values of Vm_(H2O) and SA_(H2O)/SA_(N2) ratio, meaning the higher adsorption ability for ZEA. The ZEA adsorption ability of the HE-K sample heated at 773 K was the largest in all the clay adsorbents except the reference samples.