Question

Draw and explain the structure of different types of clays

Answer 1

The different type of clay minerals are-

1) Kaolinite:

In this type of clay mineral silica tetrahedral layer (S) is joined with one aluminium octahedral layer (G). The total thickness of one structural unit is 7 Angstrom. Bond in the structural unit is Hydrogen bond which exists between the oxygen of silica sheet and hydroxyl ion of alumina sheet. Since the bond is very strong hence water can not enter between units. So mineral is quite stable and shows no expansion.

2) Montmorillonite-

In the basic structural unit, an alumina sheet(G) is sandwiched between two silica sheet (S). The total thickness of each structural unit is 10 angstrom. Two units are joined by the bond formed between oxygen ions of two different silica sheet. So a weak Vander Waal forces exist and water molecules can enter between two structural units. so, such a clay may show swelling.

3) Illite-

The basic structural unit looks like montmorillonite. However, this mineral has different properties. The link between two different units is due to non-exchangeable potassium ion. The lattice of illite is also stronger. It swells less than montmorillonite.

Above three are the most important type of clay structures. However, some other types of structures include-

Allophanes- It is a random asymmetrical distribution of silica tetrahedra and aluminium octahedra.

Chlorite- it is made up of one unit of a vermiculite layer and one unit of a magnesium octahedral layer.

Vermiculite- contains two silica tetrahedral layers and one octahedral layer.