Sintering and devitrification of glass-powder compacts in the akermanite-gehlenite system

The sintering and devitrification behavior of glass-powder compacts with four compositions, Ca2Mg0.5Al1.0Si1.5O7, Ca2Mg0.6Al0.8Si1.6O7, Ca2Mg0.7Al0.6Si1.7O7, and Ca2Mg0.8Al0.4Si1.8O7, corresponding to akermanite-gehlenite ratios (mol%) of 50/50, 60/40, 70/30, and 80/20 were investigated. Glass frits were prepared by the classical melt quenching technique in water. The structure of the glasses was investigated using FTIR and NMR, whereas the sintering behavior was studied by DTA and HSM. Sintering precedes crystallization only in Ca2Mg0.5Al1.0Si1.5O7 glass while in the remaining glass compositions maximum densification was achieved slight after the onset of crystallization. However, the ratios of final area/initial area (A/A (0)) of the glass-powder compact ranging from 0.63 to 0.66 imply towards good densification levels (95-98 %) achieved in the investigated glasses. Qualitative and quantitative XRD analyzes were performed in glass-powder compacts heat treated at 900 and 1000 A degrees C. Merwinite was found to crystallize first followed by decomposition at higher temperatures to form akermanite-like phase

Water-rock interactions: An investigation of the relationships between mineralogy and groundwater composition and flow in a subtropical basalt aquifer

A holistic study of the composition of the basalt groundwaters of the Atherton Tablelands region in Queensland, Australia was undertaken to elucidate possible mechanisms for the evolution of these very low salinity, silica- and bicarbonate-rich groundwaters. It is proposed that aluminosilicate mineral weathering is the major contributing process to the overall composition of the basalt groundwaters. The groundwaters approach equilibrium with respect to the primary minerals with increasing pH and are mostly in equilibrium with the major secondary minerals (kaolinite and smectite), and other secondary phases such as goethite, hematite, and gibbsite, which are common accessory minerals in the Atherton basalts. The mineralogy of the basalt rocks, which has been examined using X-ray diffraction and whole rock geochemistry methods, supports the proposed model for the hydrogeochemical evolution of these groundwaters: precipitation + CO 2 (atmospheric + soil) + pyroxene + feldspars + olivine yields H 4SiO 4, HCO 3 -, Mg 2+, Na +, Ca 2+ + kaolinite and smectite clays + amorphous or crystalline silica + accessory minerals (hematite, goethite, gibbsite, carbonates, zeolites, and pyrite). The variations in the mineralogical content of these basalts also provide insights into the controls on groundwater storage and movement in this aquifer system. The fresh and weathered vesicular basalts are considered to be important in terms of zones of groundwater occurrence, while the fractures in the massive basalt are important pathways for groundwater movement