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SOIL FORMATION - Coggle Diagram

- - - - Primary minerals
        
        are those which are not altered chemically since the time of formation and deposition
        
        This group includes quartz, feldspar (alumina silicates containing varying amounts of sodium, potassium), micas (muscovite, chlorite), amphibole (hornblende: magnesium iron silicates), etc
        
        Primary minerals are non-clay minerals with low surface area (silica minerals) and with low reactivity. These minerals mainly affect the physical transport of liquid and vapors
      - Secondary minerals
        
        are formed by the decomposition and
        chemical alteration of primary minerals
        
        Some of these minerals include kaolinite, smectite,
        vermiculite, gibbsite, calcite, gypsum, etc.
        
        These secondary minerals are mostly layered alumina-silicates, which are made up of
        silicon/oxygen tetrahedral sheets and aluminum/oxygen octahedral sheets.
        
        Secondary minerals are clay minerals with high surface area and high reactivity that affect the chemical transport of liquid and vapors
  - - - This induces plasticity in clay
      - Therefore, plasticity increases with SSA. Water in clays exhibits negative pressure due to which two particles are held close to each other
      - Clay attracts dipolar water towards its surface by adsorption
      - Due to this, apparent cohesion is developed
        in clays
    - - A lot of engineering properties of soil is affected by this behavior and the stability of structures founded on such soils become detrimental.
      - The swelling of clay minerals decreases in the order montmorillonite > illite > kaolinite
      - Some clay minerals when exposed to moisture are subjected to excessive swelling and during drying undergo excessive shrinkage
    - - Defined as the surface area of soil particles per unit mass (or volume) of dry soil. Its unit is in m2/g or m2/m3
      - Clay minerals are characterized by high specific surface area (SSA) as listed
        in the table below
      - High specific surface area is associated with high soil-water-contaminant interaction, which indicates high reactivity
        
        The reactivity increases in the order Kaolinite < Illite < Montmorillonite
        
        For the purpose of comparison, SSA of silt and sand has also been added in the table
        
        There is a broad range of SSA values of soils, the maximum being for montmorillonite and minimum for sand. As particle size increases SSA decreases
- - - - The deposits of gravel, sand, silt, and clay formed by weathering may become compacted by
        overburden pressure and cemented by agents like iron oxide, calcite, dolomite, and quartz.
      - Cementing agents are generally carried in solution by groundwater
      - They fill the spaces
        between particles and form sedimentary rock
    - - Metamorphism
        
        is the process of changing the composition and texture of rocks (without
        melting) by heat and pressure
        
        During metamorphism, new minerals are formed, and mineral
        grains are sheared to give a foliated texture to metamorphic rock.
    - - are formed by the solidification of molten magma ejected from deep within the
        earth’s mantle.
- - - - It may be caused by the expansion and contraction of rocks from the
        continuous gain and loss of heat, which results in ultimate disintegration
      - Frequently, water seeps into
        the pores and existing cracks in rock
      - As the temperature drops, the water freezes and expands. The pressure exerted by ice because of volume expansion is strong enough to break down even large rocks
      - Other physical agents that help disintegrate rocks are glacier ice, wind, the running water of streams and rivers, and ocean waves. Note that the soils formed by mechanical weathering bear a similarity in certain properties to the minerals in the parent or original rock, since chemical changes
        which could destroy their identity do not take place
    - - Water and carbon dioxide from the atmosphere form carbonic acid, which reacts
        with the existing rock minerals to form new minerals and soluble salts
      - Soluble salts present in the
        groundwater and organic acids formed from decayed organic matter also cause chemical weathering
      - the original rock minerals are transformed into new minerals by chemical reaction
- - - - formed by deposition in quiet lakes
    - - formed by deposition in the seas
    - - transported by running water and deposited along streams
    - - transported and deposited by wind
    - - formed by transportation and deposition of glaciers
    - - formed by movement of soil from its original place by gravity, such as
        during landslides