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A correlation was found between the net layer charge and the percentage of nonexchangeable potassium in 2:1 clay minerals having negative charges per half unit cell >0.45. This charge also marks the limit between low-charge smectites having entirely exchangeable cations and other 2:1 clay minerals. Furthermore, on samples prepared at 0.032 bar suction pressure, water retention decreased as the layer charge increased. Transmission electron micrographs, carried out so as to preserve the microstructure of the clay, also showed a relationship between layer charge, stability, and texture. For low-charge smectites (<0.45/half unit cell) exchanged with Na, clay particles were mainly individual crystals. Ca-exchanged clay particles, however, were arranged face-to-face in the form of “quasi-crystals.” High-charge illites (layer charge = 0.8/half unit cell) occurred as stable aggregates that appeared to be characteristic of these minerals. An intermediate behavior was noted for smectites having charges between 0.45 and 0.6/half unit cell.

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