Calcium smectite

Hydrated calcium silicate minerals such as xonotlite, truscottite, and gyrolite are rare but have been reported from several Au-Ag deposits. They do not coexist with Au-Ag minerals but instead are found with quartz, carbonates, and johannsenite. However, in the Keisen No. 3-2 vein in the Hishikari Au-Ag deposits, a close association of electrum with truscottite, smectite and calcite is observed (Imai and Uto, 2001). 

Products of this type seem to protect the humus from rapid incorporation into new biological processes. Additional factors that appear to be associated with the accumulation of organic matter in Mollisols are high exchange capacities, saturation with calcium, an abundance of mineral colloids and a high content of minerals of the smectite group (Fenton, 1983). 

An interaction potential between the surface and ions may also be needed in simulating counterion diffusion for the smectite and mica surface models. The form of such an interaction potential remains to be determined. This may not pose a significant problem, since recent evidence (40) suggests that over 98% of the cations near smectite surfaces lie within the shear plane. For specifically adsorbed cations such as potassium or calcium, the surface-ion interactions can also be neglected if it is assumed that cation diffusion contributes little to the water structure. In simulating the interaction potential between counterions and interfacial water, a water-ion interaction potential similar to those already developed for MD simulations (41-43) could be specified. 

The mineralogical composition of Sahara dust particles shows the predominance of aluminosilicates (clays). Illite is also present in many cases while quartz particles are rare. Scanning Electron Microscopy (SEM) results on dust composition transported over different regions in the Mediterranean Basin have shown that Al-rich clay minerals such as illite and kaolinite are very common in PM10 for Cypms and dominant for Crete. Dust particles are also very rich in calcium which is distributed between calcite, dolomite and sulphates and Ca-Si particles (e.g. smectites) whereas iron oxides are often detected [43]. 

Laser granulometry indicated little variation in the particle size with depth in the trench section, the median size being 12-15 pm. On average the bulk sediments were found to contain approximately 20% clay ( < 2 pm), 70% silt (2-63 pm) and < 10% sand ( > 63 pm). Bulk sediment XRF analyses also showed that the major element proportions are also relatively constant with depth (Figure 7.7). X-ray diffraction (XRD) analyses showed some variability in the relative proportions of clay minerals present in the < 2 pm fraction, but all samples were dominated by illite, smectite, kaolinite and chlorite. The calcium carbonate content was low ( < 1%), much of the detrital material apparently having been dissolved. The sediment pH ranged from 6.2 to 6.7. 

Smectites, by virtue of their large surface area, are particularly sensitive to the exchangeable cation type. In nature, the most common cations are Ca and Na. Calcium ions reduce bound water layer thickness and provide some deformation resistance by cross-linking clay platelet surfaces. Sodium smectite, on the other hand, has the highest affinity for water of any common phyllosilicate, and is therefore used in water-based muds (WBM) to build viscosity and to suspend fine-grained materials used to increase the mud weight. The most geochemically sensitive shales are almost invariably smectitic with saline pore fluids. 

Smectite clays consist of 1 nm thick aluminosilicate layers separated by sodium and calcium counterions. As little as 1 to 5 wt% of these layered clays can significantly improve the mechanical properties of nylon, polyolefins, and other polymers (78). Delaminating the clay structure by replacement of the sodium or calcium ions with a polymer-compatible surfactant, a quaternary ammonium ion surfactant, for example, is essential to generate a large polymer-clay interfacial area, as shown in Figure 11.21 (79). Ammonium ion head groups of the dispersant bind to the surface of the clay by Coulombic forces, and the hydrophobic alkyl tails bind to the polymer by van der Waals forces. 

Silicic acid, aluminum sodium salt. See Sodium silicoaluminate Silicic acid, calcium salt. See Calcium metasilicate Calcium silicate Silicic acid, calcium salt (1 1). See Calcium metasilicate Silicic acid, disodium salt. See Sodium metasilicate Silicic acid hydrate Silicic acid hydrated. See Silica, hydrated Silicic acid, lithium, magnesium, sodium salt. See Smectite Silicic acid, potassium salt. See Potassium silicate Silicic acid (HjSiOj), calcium salt (1 1). See Calcium metasilicate Silicic acid, sodium salt. See Sodium silicate Silicic acid, tetraethyl ester. See Ethyl silicate... 

Many nanodays are based on the smectite clay, montmorillonite, a hydrated sodium calcium aluminum magnesium silicate hydroxide, (Na,Ca)(Al, Mg)6(Si40io)3 (OH) wH 2O. M ontmorillonite is found throughout the world in small quantities in its natural geological state. In large deposits, where the mineral is found in greater than 50% concentrations admixed vdth a variety of other minerals, it is known as bentonite. 

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