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CH3041
SOIL FORMATION
• Secondary minerals are formed in the soil
from primary minerals due to the lack of
thermodynamic stability of the 1o minerals.
After the 1o minerals have been physically weathered to a small particle size the chemical decompositn 
is kinetically fast.
Relative amount
sand   50  silt   2  clay
    particle size (mm)
Secondary Minerals
            layer silicate clays,
               oxides, non-xyst.
                 aluminosilicates
Primary Minerals
quartz,  feldspar.
mica
• The major chemically
reactive fractions in
soil are the secondary
clay minerals and
the organic matter
(humus).