Feldspars weathering

ABSTRACT A geochemical analysis of major, trace and rare earth elements was carried out in beach sands collected from the Northeastern coast of Mexico in order to observe the spatial trends along three different beaches. Results show that major elements patterns along the beaches are controlled by heavy minerals and plutonic and sedimentary input towards the coast. In addition, trace elements tendencies indicate that the beach sands are influenced by the presence of magnetite. Finally, the differences in Eu anomalies indicate a mix of felsic to mafic and intermediate rocks and feldspar weathering. 

Rare earth elements trends show a negative and positive Eu anomalies in some samples studied from the Northeastern beaches suggesting a mix of felsic and mafic source rocks and feldspar weathering. 

Influence of Surface Area, Surface Characteristics, and Solution Composition on Feldspar Weathering Rates... 

Either the intrinsic surface area and characteristics of natural materials are significantly different from those used in laboratory experiments, or other non-mineralogical factors must account for the disparity between laboratory- and field-determined rates of feldspar weathering. 

Rates of Feldspar Weathering in Natural Weathering Profiles from Geochemical Mass Balance of Small Watersheds... 

Rates estimated in the above studies are shown in Table I. Watershed-scale geochemical mass balance studies yield calculated feldspar weathering rates one to three orders of magnitude slower than rates determined in laboratory experiments. 

The range of variability in feldspar weathering rates due to fine particles, strained surfaces, defects and dislocation outcrops, and surface layers is too small to account for the... 

China Clay, The product obtd by leaching weathered deposits of granitic rocks, so that quartz mica portions are removed (Ref 1). For example, when Feldspar weathers, the first product is Cornish stone this next becomes china clay rock from which the china clay is obtd. The purest china clay is known as kaolin and consists mainly of hydrated aluminum silicate(Ref 2)... 

A number of workers (Wollast, 1967 Huang and Kiang, 1972 Luce et al., 1972) have observed that feldspar weathering conforms to the parabolic diffusion law (Chapter 2). An example of this is shown in Fig. 7.2. Much research effort has gone into explaining why parabolic kinetics could be operational for feldspar dissolution. Several explanations have been given, and these are discussed below. 

However, as Velbel (1985) stated so well, more research is needed to see whether the above mechanism is operational under field conditions. We know that rates of mineral weathering are often lower in the field than in the laboratory. Natural feldspar weathering may be one to three times slower in the field (Paces, 1973). Velbel (1985) found that the rate of... 

Velbel, M. A. (1986). Influence of surface area, surface characteristics, and solution composition on feldspar weathering rates. ACS Symp. Ser. 323, 615-634. 

Berner, R. A., and Holdren, G. R., Jr. (1977). Mechanism of feldspar weathering Some observational evidence. Geology 5, 369-372. 

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