Clay minerals, formation

Michalopoulos, P. and Aller, R. C. (1995). Rapid clay mineral formation in Amazon Delta sediments reverse weathering and oceanic elemental cycles. Science 270, 614-617. 

The chemical weathering of crustal rock was discussed in Chapter 14 from the perspective of clay mineral formation. It was shown that acid attack of igneous silicates produces dissolved ions and a weathered solid residue, called a clay mineral. Examples of these weathering reactions were shown in Table 14.1 using CO2 + H2O as the acid (carbonic acid). Other minerals that undergo terrestrial weathering include the evaporites, biogenic carbonates, and sulfides. Their contributions to the major ion content of river water are shown in Table 21.1. 

REX (R.W.) and MARTIN (B.D.), 1966. Clay mineral formation in sea water by submarine weathering of K-feldspar. Clays and Clay Min. 14,... 

Price JR, Velbel MA, Patino LC (2005) Rates and time scales of clay-mineral formation by weathering in saprolitic regoliths of the southeren Appalachians from geochemical mass balance. Geol Soc Am Bull 117 783-794... 

DeKimpe, C.R., Gastuche, M.C. and Brindley, G.W., 1961. Ionic coordination in alumino- silicic gels in relation to clay mineral formation. Am. Mineralogist, 46 1370-1381. 

Hawkins, D.B. and Roy, R., 1963. Experimental hydrothermal studies on rock alteration and clay mineral formations. Geochim. Cosmochim. Acta, 27 1047-1054. 

McMurtry G. M. and Yeh H.-W. (1981) Hydrothermal clay mineral formation of East Pacific Rise and Bauer Basin sediments. Chem. Geol. 32, 189-205. 

Wider controls on soil and clay mineral formation... 

Figure 9.7 Clay mineral composition of the surface layers of residual soils formed on (a) quartz- and feldspar-rich rocks, and (b) Fe- and Mg-rich igneous rocks in California. After I Barshad. The effect of variation in precipitation on the nature of clay mineral formation in soils from acid and basic igneous rocks, Prac. Int. Clay Conf., 19 by the Geological Survey of Norway. Used by permission.

Barshad, I. 1966. The effect of variation in precipitation on the nature of clay mineral formation in soils from acid and basic igneous rocks. Proc. int. clayconf. Jerusalem 1, pp. 167-73. 

The first two pathways of formation will not be discussed here as they were found to be only of local/regional importance and are not eonsidered to be of major importance for early diagenetic reactions. Iron bearing clay mineral formation under high-temperatnre conditions near a hydro-thermal system of the Red Sea was studied by Bischoff (1972). A direct precipitation of an iron-rich smectite (nontronite) within the metalliferons sediments was found. This pathway of clay mineral formation was shown to occur at temperatures... 

During clay mineral formation 0 and D are enriched in the newly formed mineral. The isotope fractionation between mineral and fluids in isotopic equilibrium is a function of the temperature. The isotopic composition of the parent rock is negligible (Yeh and Savin, 1977), especially when large water - rock ratios can be expected during the early stage of alteration. 

Eberl, D.D. (1984). Clay mineral formation and transformation in rocks and soils. Phil. Trans. R. Soc. Lond. A, 311 241-257. 

Figure 4.16 Schematic representation of smectite clay minerals formation and structure.

While inheritance dominates in the sedimentary environment at generally ambient conditions characterized by slow reaction rates, layer transformation requires a considerable input of activation energy, and thus is found preferentially in the diagenetic and hydrothermal realms, where higher temperatures prevail. In between these two environments, the weathering environment exists in which all three mechanisms discussed above can be operational. Hence, when these three mechanisms occur in three different geologic environments, it leads to nine pos-sibiUties of clay mineral formation in nature, attesting to the exceptional variability and complexity of day mineral chemistries. 

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