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Constancy of the Sum of Mica Unit Cell Potassium Surface and Interlayer Sorption Surface in Vermiculite-Illite Clays¹

ABSTRACT

The total unit cell planar specific surface was computed as the sum of planar sorption surface (by a glycerol gravimetric method) and the mica unit cell interplanar surface (corresponding to the K). This sum was found to be constant for a given unit cell formula weight, averaging 773 m.²/g. with a standard deviation of ±12.7 or about ±2%. For example, a Colorado vermiculite had 1.63% K₂O equivalent to 16.3% mica residue with a unit cell interplanar surface of 124 m.²/g.; this added to the measured 631 m.²/g. of planar sorption surface (glycerol sorbed on expanded or cleavage planes) gives a total planar surface of 755 m.²/g. Similarly, for coarse clay from Fithian, Illinois, the 5.61% K₂O is equivalent to 56.1% of illite, with unit cell interplanar surface of 426 m.²/g. This, added to 235 m.²/g. of measured planar sorption surface, gives a total of 661 m.²/g. which when corrected to exclude 15% unexpanded minerals (kaolinite and chlorite) gives a total planar specific surface of 775 m.²/g. Wyoming montmorillonite had 803 m.²/g. of planar specific surface, comparing well with the theoretical, 808 m.²/g. This principle of unit cell planar specific surface constancy of 2:1 layer silicates shows that the mechanism of K release from mica is by cleavage, and gives an accurate tool for analysis of the rather generally occurring interstratified mixtures of expanding 2:1 layer silicate minerals with micas in soils and sediments.

Contribution from the Department of Soils, University of Wisconsin, Madison, supported in part by the University Research Committee through a grant of funds from the Wisconsin Alumni Research Foundation. Presented before Div. II, Soil Science Society of America, Atlanta, Ga., Nov. 19, 1957.

² Graduate Assistant and Professor of Soils, respectively.

Received for publication July 30, 1958. Accepted for publication September 19, 1958.

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				C. Weaver and C. E. Weaver Potassium Content of Illite Science, February 5, 1965; 147(3658): 603 - 605. [Abstract] [PDF]

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