Chemical Weathering of Glauconite1
- Gilani Abudelgawad,
- A. L. Page and
- L. J. Lund2
Glauconite samples were collected from geologic cuts in the Barce Plateau in the eastern part of Libya. The glauconite was associated with limestone, dolomitic limestone, marl, marl stone, chert, and kaolinite. Samples of the glauconite from the area of study after removal of carbonates gave X-ray diffraction spacings of 10.0, 7.2, 5.0, 3.6 and 3.3 Å. Spacings of 10.0, 5.0, and 3.3 Å represent the 001, 002, and 003 reflection of micaceous components. Spacings of 7.2 and 3.6 Å were due to kaolinite. No 060 reflection was observed for random samples. The absence of this spacing, although not entirely specific for glauconite, is indicative of glauconite-like minerals. Petrographic analysis and chemical composition confirmed that the micaceous mineral studied was glauconite. (The term glauconite in the area of the study was given by the field geologist based upon the morphology of the micaceous material.)
Potassium depletion of the glauconite by sodium tetraphenyl boron (NaTPB) treatment produced diffraction spacings of 14 to 15 Å when Mg saturated. Amounts of K removed by NaTPB and by exhaustive treatments with 1N NaCl were 183 and 179 meq/100 grams, respectively, which were about 95% of the total potassium as determined by Na2CO3 fusion. This demonstrated that essentially all of the K in the glauconite is of interlayer origin.
Equilibrium studies showed that the rate of K removed from the glauconite by 1N NaCl was dependent upon contact time and suspension density. Selectivity coefficients for the exchange of K by Na at equilibrium were about 2500. Infrared spectra of K-depleted glauconites were quite similar to the IR spectrum of the specimen layer silicate nontronite. Amounts of K removed by and cation exchange capacities following selective K depletion techniques, the chemical composition, X-ray diffraction and the infrared spectra show that K-depletion of glauconite gives rise to an iron rich vermiculite.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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