ChemicalChemical WeatheringWeathering

Chemical Weathering• Chemical weathering - process by

which the internal structure of a mineral is altered by the addition or removal of elements. 

  

Factors that influence chemical weathering

• Climate Living Organisms    acid production and mineral decomposition

• Time • Mineral composition • Chemical Weathering Products

    Clays     Metals ores     Rounding of boulders (chemical exfoliation)

1. Carbonation• Process by which dissolved carbon dioxide

in rainwater forms carbonic acid and reacts with the minerals in the rock.

• This process weakens the rock thus breaking it down in the process.

• H20 +C02 H2C03

• (water + carbon dioxide carbonic acid)• Most effective agent of chemical

weathering: Carbonic acid!

2. Hydrolysis• chemical reaction between the minerals in

the rock and hydrogen in rain  water. • For example, during hydrolysis, the

feldspar in granite changes to clay mineral which crumbles easily, weakening the rock and causing it to break down.

• http://www.classzone.com/books/earth_science/terc/content/visualizations/es1202/es1202page01.cfm?chapter_no=visualization

3. Oxidation• The process by which oxygen combines

with water and minerals in the rock such as calcium and magnesium.

• When iron reacts with oxygen, reddish -brown iron oxide is formed.

• The iron-oxide crust crumbles easily and weakens the rock.

• e.g. : Iron + Oxygen -->  Iron Oxide (crumbles)

4. Solution• process by which minerals in the rocks

dissolve directly in water. • Rainwater can dissolve statues and

tombstones made of marble (mostly calcite)

• CaCO3 + CO2 + H2O Ca+ + 2 HCO3-

• (calcite + carbon dioxide + water Calcium ion + bicarbonate ion (liquid))

Stalactites and Stalagmites• Caves and caverns typically form in limestone

– stalactites - hang from ceiling – stalagmites - on the ground

• http://www.goodearthgraphics.com/virtcave/staltite/staltite.html• http://www.goodearthgraphics.com/virtcave/stalmite/stalmite.html

5. Hydration• process where minerals in the rock absorb

water and expand, creating stress which causes the disintegration of rocks.

• EG: Unhydrated Calcium sulphate + Water -->   Hydrated Calcium Sulphate (expands)

In text:

• Page 112 read article 5.1 make notes• Finish this web:

• Page 120 question 12,13,14,15,16