A) Mechanical / Physical weathering:

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A) Mechanical / Physical weathering

• Never in isolation
• Granular disintegration

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• Frost
  shattering

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Insolationweathering
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Wetting and drying (slaking)
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Exfoliation (spheroidal weathering)
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• Salt crystal growth

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• pressure release - dilation

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Organic action
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B) Chemical Weathering

• decomposition of minerals so the chemistry of
  the rock is altered.
• H2O CO2 ltgt H2CO3
• Best in warm, humid conditions

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Hydrolysis

• H ions in water react to give clays.
• Rocks containing feldspar are particularly
  vulnerable (eg granite)

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Hydration

• the absorption of water into the crystal
  structure can weaken the rock
• Also a physical process (brown flakes)

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Carbonation

• H2CO3 CaCO3 ltgt Ca (HCO3)2
• Calcium hydrogen carbonate (or calcium
  bicarbonate) is very soluble in water and so the
  limestone dissolves

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(No Transcript)
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Solution

• Some rocks simply dissolve eg halite (rock salt)

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Oxidation

• Minerals react with oxygen to form oxides or
  hydroxides
• eg rusting, where iron in ferrous form is
  oxidised into its ferric form

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Humic (organic) acid from decaying flora
fauna attack certain minerals

• Lichens extract iron

Chelation
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Rates of weathering depend on

• Rock type quartz is unaffected by solution,
  hydrolysis and oxidation
• (sand on a beach)

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Rock structure(joints)
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Climate

• A temperature range
• Water
• Vegetation