Hydrolysis
when mineral is broken down by reaction with reaction. occurs in acid conditions.
important in silicate minerals that form most rocks, especially the mineral feldspar.
reaction includes carbonation. produces clay residue and various solutions which
are removed in groundwater, found in analysis of river water.
other clays are produced from other silicate minerals e.g. montmorillonite
Hydration and dehydration
wetting and drying can cause addition/removal of water from molecules of some
minerals, causing expansion/contraction, assists disintegration. calcium sulphate
minerals (anhydrite and gypsum) are affected.
Carbonation
process affects carbonate minerals that make up limestone. rainwater contains the
weak acid (carbonic acid) forms as rain absorbs atmospheric CO2. carbonic acid
attacks carbonate minerals. calcium hydrogen carbonate is removed in solution,
washed away down rivers. muddy insoluble impurities in the limestone are left as
clay residue. process is responsible for the characteristic limestone scenery (karst).
chemical W of limestone accelerated by pollutants.
Organic action – vegetation roots
biological W can have physical effect in rocks as seen in wedging effect of tree
roots. shallow soil so seeds/roots find way into natural cracks in bedrock. they
make cracks wider and deeper, breaks up bedrock. seen in quarry and road
cuttings
examples of other biological effects that tend to assist chemical processes: release
of humid acids by decaying vegetation encourages hydrolysis. release of carbon
dioxide by plants encourages carbonation. blanket of vegetation traps water and
encourages a variety of chemical processes.
