Kaolinite precipitation during

There is no proof, liowever, that the weathered material has derived from the exact parent rock given in the table. This may explain the excess in soil vol % quartz, which, assuming quartz is not dissolved or precipitated during soil formation and that volume and weight percents are roughly equal, should not exceed about (30/75) x 100 = 40 wt % of the soil. (Densities of quartz, K-feldspar, plagioclase feldspar, and kaolinite are alt 2.60 0.05 g/cm ). 

During the process of weathering, new kinds of minerals, the secondary minerals, are synthesised. As well as precipitates (hydroxides, oxides, sulphates, carbonates and phosphates) there are the clay minerals. For example, potassium feldspar can hydrolyse and lead to the formation of kaolinite ... 

The thin, clay and iron-rich red layer caps a transition to a calmer water depositional environment. The red layer is predominantly composed of quiet water clay laminae, but at least five separate episodes of turbulent flow introduced clay rip-up clasts into the system. The red layer marks the last occurrence of remobilized clay clasts. These were in turn covered by laminae deposited during the quieter phase of flow. The high iron and kaolinite clay contents suggest an influx of weathered soil sediment. The iron enriched caps on fining upward laminae implies that an extraordinary amount of iron was allowed to settle or precipitate out in quiet water. 

Now if K-feldspar continues to dissolve (or, if you prefer, we continue to perform speciation calculations for solutions in which K, Al, and Si continue to increase in the ratio 1 1 3), gibbsite will continue to precipitate, and the remaining solution will have compositions that follow the path A B on Figure 19.5. During this process, the silica content of the solution continues to increase until at point B, a silica-bearing mineral (kaolinite) becomes stable. The coexistence of gibbsite and kaolinite buffers the activity of silica according to... 

Since precipitation has often been observed during adsorption studies when surfactants are contacted with certain mineral suspensions, the role of it in determining the nature of isotherms for the important reservoir system made up of kaolinite and dodecylbenzenesulfonate was investigated in this study. Results showed a complex and interesting behavior of the system involving precipitation followed by redissolution at higher sulfonate concentrations that was markedly dependent upon the salt concentration and the type of inorganic ions involved (5). Also, the phenomenon of precipitation and redissolution whenever it occurred proved to have a definite influence on the shape of the isotherm. 

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