Chemical weathering process

Chemical weathering

Chemical weathering refers to the disintegration of rock as a result of chemical changes in the mineral composition if the rock.

The four main processes of chemical weathering are: solution, hydration, oxidation and carbonation.

Carbonation

Carbonation is caused by rainwater that has absorbed carbon dioxide from the atmosphere to form a weak carbonic acid.

The slightly acidic rainwater dissolves certain minerals in the rock

formation of the burren

Limestone is an alkaline rock with a component called calcium carbonate within it due to the seashell fragments that help form the rock.

As rainwater falls it absorbs carbon dioxide that is in the atmosphere. It turns into a weak carbonic acid that reacts with the alkaline calcium carbonate within the limestone rock.

The reaction forms calcium bicarbonate that is soluble that can be easily washed away by the rainwater.

The removal of dissolved calcium bicarbonate by rainwater is called solution.

As limestone is a permeable rock composed of layers and vertical joints, water often soaks within the rock and weathers it to form features.

These features are grikes, clint and karrens which can be seen in the karst landscape of the limestone pavement in the Burren Co.Clare.

Caverns and dripstone deposits

Carbonation has also created a distinctive landscape below the surface of the Burren.

It can lead to caves forming such as the Ailwee Caves. This happens when a river disappears underground through a swallow hole, leading to a passage being created.

Many dripstone features can be seen in these caves or caverns, such as stalactites, stalagmites and pillars.

Stalactites form when drops of water containing dissolved limestone seep through cracks in the cave roof.

These drops lose carbon dioxide, deposit calcite and hang down from the cave roof.

Stalagmites are formed when water droplets fall to the cave floor. They deposit calcite and build up from the floor.

Pillars are formed when stalactites and stalagmites grow towards each other and eventually meet.

Hydrolysis

• Hydrolysis is the chemical weathering of minerals by a mildly acidic water that forms when rains dissolves gases in the atmosphere.

• Hydrolysis happens faster in hot wet climates.It is very effective in weathering granite rock.

• Feldspar is one of the minerals in granite. Feldspar absorbs water easily.

• In the chemical process that takes place feldspar is converted into Kaolin (china clay).

• Feldspar is very good at holding minerals together but Kaolin is not. It crumbles easily weakening the rock.

• Together with freeze thaw action Tors can be formed on exposed Granite as a result