CLAY MINERALS

Kaolinite

Kaolinite is the most common minerals of the kaolinite group of the minerals. The basic structural unit consist of the Gibbsite sheet with the aluminium atom at the center,

The thickness of the kaolinite mineral is 7 armstrong. This mineral is join to silica sheet through unbalance oxygen atom at the apex of the silica sheet.

The structure of the kaolinite mineral are joint together by the hydrogen bond and this bond is  between the oxygen atom of silica s and the hydroxyls of gibbsite sheet.

This hydrogen bond is very strong and it is very difficult to separate the layer and water cannot penetrate through the layers of the structural unit of kaolinite minerals.

Hence , the kaolinite minerals are relatively stable.

 

MONTMORILLONITE

Montmorillonite is the most common minerals of the montmorillonite group of the clay minerals. The basic structural unit of the this group of minerals consist of the gibbsite  sheet sandwitched between two silica sheet.

The gibbsite sheet may include atoms of magnesium , iron , aluminium or combination of these.

The total structural thickness of montmorillonite is 10 armstrong.

This basic unit of momtmorillonite are joined together by a link between oxygen ions of the two silica sheet.

This link is due to natural attraction for the cations in the intervening space and due to vander wall forces.

In the montmorillonite water may enters between the silica sheet causing the minerals to swell.

ILLITE

Illite minerals is the most common mineral of the illite group of clay minerals. The basic structural unit is similar to that of montomorillonite mineral except that there is always substantial (20+-) substitution of silicon atoms by aluminium atoms in silica sheet.

The link between the different basic structural unit is through non-exchangeable potassium ions.

Thus , the properties of illite are somewhat intermediate between those of kaolinite and montmorillonite. The swelling in the illite is more than of kaolinite butless than the montmorillonite.

CONSISITENCY LIMIT

Atterberg explains  that the fine grained soil exist in four state that is liquid, plastic, semi-solid or solid state and water content at which the soil changes from one state to other is called consistency limit.