Phyllosilicate mineral

In the seawater example (Table 6.6), the saturation indices are inflated somewhat by the choice of a rather alkaline pH, reflecting equilibrium with atmospheric CO2. If we had chosen a more acidic pH within the range observed in seawater, the indices would be smaller. The choice of large formula units for the phyllosilicate minerals, as discussed later in this section, also serves to inflate the saturation indices reported for these minerals. 

Talc is a soft, large-molecule phyllosilicate mineral having a characteristic waxy luster. Ground to a floury texture, it used as bath powder and as a base for cosmetics. It is also used as a filler in food, as a dry lubricant, and in the manufacture of some kinds of paper. 

Soapstone or steatite are names generally applied to any soft, waxy or greasy, massive metamorphic rock. The dominant mineral is usually talc, a light-colored magnesium silicate. Other phyllosilicate minerals or mixtures of minerals are used in similar ways, since their relative softness makes them attractive to carvers. Massive soft soapstone has also been used to make sinks, electrical switchboards, and ovens. 

IX. Phyllosilicates. Minerals (clays) made out of O2 coordinated by metal cations and stacked in a certain sequence (Fig. 3.6). 

Another phyllosilicate mineral, namely, biotite, has larger sorption capability as expected. It is likely related to the iron content of biotite. Similarly, the carbonates containing iron and magnesium (ankerite and dolomite Table 3.8) show more significant cesium sorption as calcite (calcium carbonate), which practically does not adsorb cesium. The low sorption ability of calcite can be explained by the Hahn adsorption rule (Chapter 1, Section 1.2.4) that is, the sorption is low when the sorbate (cesium carbonate) has great solubility. 

The structural distortions of phyllosilicate minerals have been investigated by solid-state Si nuclear magnetic resonance spectroscopy (NMR) [24], In trioctahedral layer silicates such as talc, the wSi chemical-shift value is related to the amount of >VA1 substitution and/or distortion of the tetrahedral sheet structure. 

The solid-state MSi NMR spectrum of talc displays a single resonance at -98.5 ppm [24], Upon, VA1 substitution, the wSi chemical shift value is shielded (more positive ppm value), whereas further distortion of the tetrahedral sheet is reflected in a decreased chemical shift value (deshielded, increased negative ppm value). The authors of this report suggest that solid-state wSi NMR may be used to determine the compositional nature of phyllosilicate minerals. In each of these studies, the spectra were obtained at a frequency of 71.5 MHz on a Fourier transform spectrometer interfaced to a 8.45-T magnet. Tetramethylsilane (TMS) was used as an external chemical-shift standard. 

Why is the phrase clay mineral misleading, and what term is best used to describe phyllosilicate minerals of >2 gm effective diameter ... 

Greenalite An iron-rich phyllosilicate mineral found in banded iron formations. 

Montmorillonite A phyllosilicate mineral that typically forms microscopic crystals making a clay. It is the main constituent of the volcanic ash weathering... 

Mica is an aluminosilicate mineral, extracted from rocks along with quartz and sometimes feldspar. The name mica is a simplification as it actually represents a group of about 37 phyllosilicate minerals, although they all have the same characteristic layered structure. 

The term clay mineral refers to phyllosilicate minerals and to minerals which impart plasticity to clay and which harden upon drying or firing. 

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