Saponite origin

Most of the saponites described have a hydrothermal origin and have usually been formed by the action of either hydrothermal or surface waters on basic rocks. The iron-rich saponite described by Sudo (1954) occurs as a clay matrix in a Tertiary iron sand bed and is presumably authigenic. A metamorphic origin is proposed for saponite from metalimestones (Wilson et al., 1968). 

From Figure 4 it can be seen that decreasing the Si/Al ratio from 39 to 5.7 is accompanied by an increase of the Al /Al -ratio frxrm approximately 2 to 30%. 29si MASNMR measurements on Zn-saponite with Si/Al=5.7 exhibit three resonances at -96, -91 and -86 ppm (Figure S), originating from silicon coordinated with zero, one and two aluminium ions, respectively, which agrees with literature data for clay minerals [9]. 

The two end members of this group with mainly tetrahedral substitutions are beidellite and saponite, which are di- and trioctahedral smectites, respectively. The corresponding end members with mainly octahedral substitutions are mont-morillonite and hectorite. Another common smectite, nontronite, is an iron-rich mineral. Chemical compositions of various smectite samples are provided in Table 2. Montmorillonite is the most common mineral of this group it is named for its location in Montmorillon, France. Figures 3d and 3e provide SEM views of the textural morphology of two montmorillonites. A common industrial mineral is bentonite, which is actually a montmorillonite of volcanic ash origin that contains a significant amount of impurities, such as cristobalite (a-quartz), that is intimately mixed with the clay. 

In the early work of Galarneau, a host clay with a high cation exchange capacity was considered essential for the PCH formation. However, more recent PCHs have been successfully synthesized from other clays of lower charge density. Cool and Ahenach reported the formation of PCHs from natural montmorillonite and synthetic saponite and laponite (25,104). The authors reported on the existence of two different heterostructures, depending on the origin of the host clay used (natural or synthetic) as well as on a combined micro- and mesoporosity for these materials. 

Hectorite. Originally known as hector CLAY from its source near Hector, California, USA. It is a hydrous magnesium silicate related to montmorillonite and forming an end-member of the saponite series. 

Magnesium alumimun silicate is insoluble in water or alcohol, but swells to many times its original volume to form colloidal dispersions. It is practically insoluble in organic solvents. Dispersions in water at the 1% to 2% level are thin colloidal dispersions. At 3% or above the dispersions are opaque, and as the concentration is increased above 3% the viscosity of the dispersions increases rapidly and exhibits thixotropic behavior. Magnesium aluminum silicate forms a gel at levels of 10% and above. Several different grades are available differentiated by Al Mg ratio (montmorillonite saponite ratio), particle size, dispersion viscosity, and degree of chemical activity. 

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