A process of disintegration and decomposition of rocks and minerals which are brought about by physical agents and chemical processes, leading to the formation of Regolith (unconsolidated residues of the weathering rock on the earth’s surface or above the solid rocks). The process of transformation of solid rocks into parent material or Regolith. Weathering Sequence of Minerals: Climatic and biotic conditions will determine the relative stability of the various soil forming minerals. Under all climatic conditions a definite listing of minerals in relation to their resistance to weathering cannot be made. So considering the various environmental conditions and diversification the following order of weathering resistance of the sand and silt-size mineral are quartz (most resistant) > muscovite, K-feldspars > Na and Ca-feldspars >biotite hornblende and augite> olivine > dolomite and calcite > gypsum and it is subjected to change according to environmental conditions . Weathering of Igneous Rocks: For igneous rocks the most prevalent minerals are feldspars (60%), pyroxenes and amphiboles (17%), quartz (12%) and mica (4%). When this rock type weathers the feldspars disappear. This very low stability is brought about because of the low bond strength between feldspar units, and in an alkaline environment the feldspar commonly alters first to the clay mineral montmorillonite. If the environment is conducive to change, this clay mineral type will alter further. The stability of the other rock forming minerals is in the order.

1. Weathering sequence of soil with
special reference to Indian soil
Presented by
S.BARATHKUMAR
2022520004

2. Weathering
• A process of disintegration and decomposition of rocks and minerals
which are brought about by physical agents and chemical processes,
leading to the formation of Regolith (unconsolidated residues of the
weathering rock on the earth’s surface or above the solid rocks).
• The process of transformation of solid rocks into parent material or
Regolith

3. Weathering Sequence of Minerals:
• Climatic and biotic conditions will determine the relative stability of the various
soil forming minerals.
• Under all climatic conditions a definite listing of minerals in relation to their
resistance to weathering cannot be made.
• So considering the various environmental conditions and diversification the
following order of weathering resistance of the sand and silt-size mineral are
• quartz (most resistant) > muscovite, K-feldspars > Na and Ca-feldspars >biotite hornblende and
augite> olivine > dolomite and calcite > gypsum and it is subjected to change according to
environmental conditions

4. The weathering sequence as reported by Goldich (1938) is presented

5. Stages in Weathering of Minerals:

6. Weathering of Igneous Rocks
• For igneous rocks the most prevalent minerals are feldspars (60%),
pyroxenes and amphiboles (17%), quartz (12%) and mica (4%).
• When this rock type weathers the feldspars disappear. This very low
stability is brought about because of the low bond strength between
feldspar units, and in an alkaline environment the feldspar commonly
alters first to the clay mineral montmorillonite.
• If the environment is conducive to change, this clay mineral type will
alter further. The stability of the other rock forming minerals is in the
order

7. • muscovite > > > amphibole > pyroxenes > > > biotite.
• Thus it could be expected that muscovite may be present in a soil
from igneous rocks, whereas the amphiboles, pyroxenes and biotites
would be altered completely.
• A general weathering schedule for igneous rocks has been described
by Currey

8. • The agents or features which contribute to weathering of a surface
are:
(i) water charged with carbon dioxide
(ii) oxygen
(iii) acids derived from vegetation and
(iv) a system of joints through which water will penetrate.

9. Unweathered Weathered Lateritic
Weathering
Quartz
Kaolinite
Muscovite
unaffected Quart
disorganised Kaolinite
slightly altered
Muscovite
Quartz
reduced to Halloysite 2H20
severely degraded Inter-
stratified

10. Weathering of Sedimentary Rock
• Weathering of the sedimentary (Silurian Age) rocks which form the base for a
large area around Melbourne is extremely variable. Very soft or hard beds can be
formed depending on whether the parent material was mudstone, siltstone or
sandstone
• Neilson (1977) identifies three phases in the weathering of the mudstones (and
siltstones) of the Melbourne area.
(a)Early to Mid-Tertiary
(b) Lateritic weathering of pre-existing deeply weathered profiles
(c) Later weathering - the development of soil and soil minerals.