weathering 1 Flashcards
def weathering
means by which soil, rocks and mnrls are changed by phi and X processes into other soil components
def mobility
capacity for elts, ions and molecules to move from one compartment of the soil to another
factors influencinf weathering
- prop of parent rock (solubility, structure)
- climate (rainfall, T°C)
- vegetation (decomposition vegetation releases CO2 or humic and fulvic acids)
- exposure time
podzol soil profile
O : OM
A = weathering and mobilization of meteals (low pH)
B: precipitation (immobilization) pH increases to due to reactions using H+
C: unweathered soil
R = bedrock
organic acids
when metals are complexed to dissolved organic acids, they are kept in solution (complexation increases metal mobility)
whend does smectite form
climate with intermediate annual precipitation
when does gibbsite form
froms in climate with high annual precipitation, intensive leaching of weathering soils
congurent/incongruent weatherin
congruent : only dissolved irons are produced
incongruent weathering : dissolved anions and 2ndary minerals are produced
guidelines for constructing weathering reactions
- Al does not dissolve
- Excess Si forms silicic acid H2SiO4 or Si(OH)4
- alkali metals and alkaline earth metals form ions
- Quel carbonate !!!
- oxygen is balanced with H20
- hydrogen is balanced with H+
pyrite weathering
know steps
calcite weathering
congruent
feldspar weathering
incongruent
what happens to the clay mineral if the precipitation increases
With increasing rainfall clay minerals become more depleted in cations
These ions are instead washed away as dissolved ions
In gibbsite (an hydroxide) only Al is left as a cation
Kaolinite
Al2Si2O5(OH)4
cold and humid climate
smectite
0,5(Ca,Na)Al3MgSi8O20(OH)4
dry climite
gibbsite
Al(OH)3
tropical, wet climate
