Introduction to Soil Chemistry

soil solids 31
the name taken from the concept that material from the surface falls to the
bottom of the cracks, resulting in inversion of the soil.
In the field when soil containing 2:1 clays become wet, they swell shut and
water movement through them is extremely slow. In a soil profile wetting
and swelling of this type of clay will prevent downward movement of water
and associated contaminants. For this reason swelling clays are used to seal
both landfills and ponds to prevent leaching or leaking.
The crystals of 2:1 swelling clays are typically smaller than either kaolinite
or fine grained mica and thus have higher adsorption and cation exchange
capacities. However, surface adsorption will be of the same chemistry as that
in the fine micas.
2.1.3.3 Amorphous Clays
In addition to the crystalline clays described above, there are some materials
that act like clays but do not have a crystalline structure. Amorphous clays do
not have a definite X-ray diffraction pattern and are differentiated from the
crystalline clays on this basis. They are composed of mixtures of aluminum,
silicon, and other oxides and generally have high sorptive and cation exchange
capacities. Few soils contain large amounts of amorphous clays [2].
2.1.4. Soil Texture
Sand, silt, and clay are the three components of soil texture. Various relative
compositions, expressed on a percentage bases, are used to give soils a textural
name such as sandy loam, or loamy clay. For soils containing significant
amounts of silt, the term loam is used, although with high levels (>88% silt,