5.4.3 Mudrocks - Montmorillonites Smectites Group Composition, Provenance and depositional setting. скачать в хорошем качестве

5.4.3 Mudrocks - Montmorillonites Smectites Group Composition, Provenance and depositional setting.

The next class of 2 : 1 clays is known as smectites; the most familiar of these are called montmorillonite. A small amount of Mg+2 substitutes for AI+3 in the gibbsite-like octahedral sheets, creating a small net negative charge (smaller than the charge in illite). To balance this charge, the inter layers are filled mostly with Na+, K+, and Ca+2 cations. Because the charge is smaller than that of illite, water is readily absorbed in the inter layers, making the montmorillonite structure very expandable in one direction (but the structural integrity of the sheets is maintained). These clays almost double in volume when they absorb water, and they are notorious for expanding so much during saturation that hill slopes made of montmorillonite shales (and the houses built on them) can slide during heavy rains. Some sodium smectites, such can expand to 10 times their original volume.