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Chemical Weathering:

a process that breaks rocks apart through chemical changes.

Here are some elements that cause chemical weathering:

  • water
  • oxygen
  • carbon dioxide
  • living organisms
  • acid rain

Mechanical Weathering:

a process that physically breaks rocks apart

Similarities

Here are some types of mechanical weathering:

  • Ice or frost wedging
  • mechanical exfoliation (the release of pressure above a rock)
  • the growth of plants
  • animals (animals that burrow in the ground will sift soil and break up rocks)
  • abrasion

Both types of weathering are supported by wet climates.

Mechanical Weathering

Ice-wedging, also known as frost-wedging, requires water.

  • Water is pooled inside the crevices of rocks
  • The water freezes, and expands
  • The rock splits from the ice expansion

More Similarities

Both types of weathering include plants in their processes.

Mechanical Weathering

The roots of some plants will weather as they grow.

  • Especially the roots of strong trees, plants growing in rocky soil will break up the rocks with their growing roots.
  • Even the strongest rocks can be broken by some trees' roots.

A tree is weathering a rock.

Chemical Weathering

Chemical weathering also requires water. Rainfall provides water needed for chemical changes.

  • Acid rain is made of water.
  • Sulfur, carbon, and nitrogen mix with rainwater in the clouds, and create acid rain when it precipitates.
  • This rain can weather marble and limestone.

Mechanical and Chemical Weathering

More Differences

Different temperatures will encourage a different type of weathering to occur.

Chemical Weathering

Mechanical Weathering

The roots of plants produce weak acids (acids that react to water). These acids can weather limestone and marble easily.

Cold temperatures will more likely cause mechanical weathering to take place.

  • Ice wedging requires the cold for the water to freeze inside rocks.
  • Cold temperatures cause many things to expand, which will aid mechanical weathering more than hot temperatures.

Differences

The mechanical weathering process occurs differently than chemical weathering.

By Tian Wells

Mechanical Weathering

Mechanical weathering physically breaks the rocks into smaller pieces. Because of this, the mineral makeup of the new rock is the same as the original.

The outcome will still be the same as the original rock.

The water weathers the rocks as it flows.

Chemical Weathering

Chemical weathering breaks down the rock through chemical changes. Rocks that undergo chemical changes may have a different mineral composition in the result, unlike mechanical weathering.

This statue has gone through chemical weathering and developed rust, a material different from the original.

Key Vocabulary

oxidation

Chemical Weathering

  • weathering: the gradual process of wearing away and breaking down rocks
  • abrasion: where ice, wind, water, gravity, or waves wear or rub away material by friction
  • exfoliation: a mechanical weathering process which removes overlying layers and pressure of rock and causes the underlying layers to be weathered in a dome shape
  • oxidation: a chemical change in which a substance combines with oxygen, forming rust

On the other hand, hot temperatures increase the potential of chemical activity.

  • Warm temperatures also make evaporation possible, a key step to creating acid rain.
  • Heat quickens the rate at which the particles are moving, thus making the bonds between particles easy to break and reconnect to different ones, all the while increasing the chemical action.
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