A) Mechanical / Physical weathering:

• Never in isolation

• Granular disintegration

• Frost shattering:

Insolationweathering:

Wetting and drying (slaking):

Exfoliation (spheroidal weathering):

• Salt crystal growth:

• pressure release - dilation

Organic action:

B) Chemical Weathering:

• decomposition of minerals so the chemistry of the rock is altered.

• H2O + CO2 <=> H2CO3

• Best in warm, humid conditions

Hydrolysis:

• H+ ions in water react to give clays.

• Rocks containing feldspar are particularly vulnerable (eg granite)

Hydration:

• the absorption of water into the crystal structure can weaken the rock

• Also a physical process (brown flakes)

Carbonation:

• H2CO3 + CaCO3 <=> Ca (HCO3)2

• Calcium hydrogen carbonate (or calcium bicarbonate) is very soluble in water and so the limestone dissolves

Solution:

• Some rocks simply dissolve eg halite (rock salt)

Oxidation:

• Minerals react with oxygen to form oxides or hydroxides

• eg ‘rusting’, where iron in ferrous form is oxidised into its ferric form

• Humic (organic) acid from decaying flora & fauna attack certain minerals• Lichens extract iron

Chelation:

Rates of weathering depend on:

• Rock type: quartz is unaffected by solution, hydrolysis and oxidation

(sand on a beach)

Rock structure(joints):

Climate:

• A temperature ‘range’

• Water

• Vegetation