tailieunhanh - Applied Clay Mineralogy Phần 2

Các xu hướng để đường cong là do một sự khác biệt nhỏ trong kích thước của tấm silicon tứ diện và tấm nhôm tám mặt (Hình 7). | Chapter 2 Structure and Composition of the Clay Minerals 11 Fig. 5. Scanning electron micrograph of halloysite. Fig. 6. Scanning electron micrograph of kaolinite. 12 Applied Clay Mineralogy Fig. 7. Diagrammatic sketch of the structure of kaolinite and hydrated halloysite Bates et al. 1950 a kaolinite b hydrated halloysite and c proposed cause for tubular shape of hydrated halloysite. halloysite and 10 A halloysite to designate the two forms. The elongate tubular form according to Bates et al. 1950 is made up of overlapping curved sheets of the kaolinite type. The curvature develops in 10 A halloysite because of the irregular stacking of the layers and the interlayer of water molecules which cause a weak bond between the layers. The tendency to curve is caused by a slight difference in dimension of the silicon tetrahedral sheet and the alumina octahedral sheet Fig. 7 . 2. SMECTITE MINERALS The major smectite minerals are sodium montmorillonite calcium montmorillonite saponite magnesium montmorillonite nontronite iron montmorillonite hectorite lithium montmorillonite and beidellite aluminum montmorillonite . Smectite minerals are composed of two silica tetrahedral sheets with a central octahedral sheet and are designated as a 2 1 layer mineral Fig. 8 . Water molecules and cations occupy the space between the 2 1 layers. The theoretical charge distribution in the smectite layer without considering substitutions in the structure is as shown in Table 3. Chapter 2 Structure and Composition of the Clay Minerals 13 Exchangeable Cations n H20 o Oxygens Hydroxyls Aluminum iron magnesium oe Silicon occasionally aluminum Fig. 8. Diagrammatic sketch of the structure of smectites. Table 3. Charge distribution of the smectite layer 6O 4Si 4O2 OH 4Al3 4O OH 4Si4 6O 12 16 10 Plane common to tetrahedral and octahedral sheets 12 10 Plane common to tetrahedral and octahedral sheets 16 12 The theoretical formula is OH 4Si8Al4O20 NH2O interlayer and the theoretical composition without .