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Chemical and Differential Weathering

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by

Tatiana A.

on 11 March 2014

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Transcript of Chemical and Differential Weathering

Chemical Weathering/ Hydrolysis/ Acid Precip.
Chemical Weathering
The process by which rocks are broken down because of chemical interactions with the environment is called
chemical weathering.
Chemical weathering
or
decomposition
occurs when reactions on the minerals in rock.
Chemical reactions usually occur between water, rock, oxygen, co2 and acids.
Acids are formed from
hydronium ions

Hydrolysis
The change in the composition of minerals when they react chemically is called
hydrolysis.
A type of

feldspar

combines with water and clay called a

Kaolin.
Minerals that are effected by the hydrolysis often dissolve in water water can then carry the dissolved minerals to lower layers in a process called

leaching
Carbonation
When carbon doxide CO2 from the air dissolves in water H2O a weak acid called carbonic acid H2CO3 forms.
Carbonic acid has higher concentration of hydronium ions than pure water does witch speed up the process of hrdrolysis.
The conversion of minerals into carbonate is called carbonation.
Organic Acids
Acids are produced naturally by certain living organisms.
Lichens and mosses grow on rocks and produce weak acids that can weather the surface of the rock.
The acids seep into the rock and produce cracks that eventually cause the rock to break part.
Differential weathering/ Rock Composition
Oxidation
The process by which elements combine with oxygen is called
oxidation
.
Oxidation commonly occurs in rock that has iron bearing minerals, such as hematite and magnetite.
In this rock, iron, Fe, combines quickly with oxygen, O2, that is dissolved in water to form rust, or iron oxide, Fe2O3:
4Fe+3O2 Fe2O3
Differential Weathering
The process by which softer, less weather-resistant rock wears away and leaves harder, more resistant rock behind is called
differential weathering
.
Mineral quartz are exposed on Earth's surface, they remain basically unchanged, even after all the surrounding rock has weathered away.
These characteristics also make quartz a very hard mineral, so it resists mechanical weathering.
Rock composition
Sedimentary rock are affected by mechanical weathering processes.
Shales and sandstones that are not firmly cemented gradually break up to become clay and sand particles.
Conglomerates and sandstones that are strongly cemented by silicates resist weathering longer than some igneous rocks do.
Acid precipitation
acid precipitation is caused by fossil fuels and nitrogen,sulfur and other chemicals being burned in the air and mixing with the water in the air this later causes acid precipitation.This can weather away rock faster than regular rain.
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