Unit cells, dimensions kaolinite

Table 1. Atomic Coordinates for the Structure of Kaolinite Expressed in Fractions of Unit-Cell Dimensions (from Drits and Kashaev [I960]).

Figure 6. Distorted tetrahedral network of kaolinite projected on the xyO plane. The numbers on the oxygen ions correspond to those given in Table 1. Joins A and C are rotated in a clockwise manner, and joins B and D are rotated in a counterclockwise manner away from the ideal hexagonal array. The unit cell is shown by the dashed lines. The a dimension is smaller than the b dimension. (Modified from Drits and Kashaev [I960].)...

A less common form of the mineral is orthochrysotile with virtually identical cell dimensions but with p = 90°. Zvyagin [1967] suggests that this mineral has a difierent stacking sequence in the unit cell from clinochrysotile, which tends to resemble the kaolinite or dickite stacking. However, the chrysotile minerals have many defects and irregularities in their structures, and the unit-cell concept is not strictly applicable. The best we can say is that the two modifications can be described by monoclinic and orthorhombic cells. 

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