The Breaking Down of Rocks by Different Types of Weathering

Weathering rocks is most often called the breaking down of rocks or the dissolving of rocks.  This process of weathering involves larger rocks being broken down into smaller rocks.  Only natural occurrences on the surface of the earth are considered to be part of weathering rocks.

There are two different types of weathering most people refer to when it comes to the breaking down of rocks.  The first type is mechanical weathering, which is often referred to as physical weathering.  The second type is chemical weathering.

There is another type of weathering called biological weathering.  This type of weathering is often put as a separate, or third, type of weathering.  Biological weathering can easily be included in the other two types of weathering.  I will get into more detail below.

Weathering can generally be applied to a broad use of the word when discussing decomposition of various materials.  Many talk about weathering as if the word can ONLY be applied when talking about rocks.

In this article I will refer to weathering, or the weathering of rocks, as the breaking down of rocks and minerals.  I will go into the two different types of weathering with the inclusion of biological weathering as a third type of weathering.

The Mechanical, or Physical, Type of Weathering

The definition for mechanical weathering of rocks is the process to break down rocks by nature’s use of water, salt, abrasion and impact, temperature, and exfoliation.  Mechanical weathering of rock, sometimes called physical weathering, is more commonly thought of than that chemical and biological weathering.  

The best example of mechanical weathering of rocks is by water through absorption, freezing, and thawing.  Rocks will often absorb water or water will seep into cracks and crevices.  Once the water is set, changing temperatures will cause rocks to weather quickly. 

When water freezes it can slightly expand.  A tremendous amount of force from this expansion will push rocks apart.  The water can then thaw out to liquid again creating more room for additional water.  The process can continuously repeat in transitioning seasons where temperatures can be warmer during the day and freezing at night.

Examples of mechanical weathering are:

• Weathering by Water
• Salt Weathering
• Abrasion and Impact Weathering
• Temperature weathering
• Exfoliation Weathering
• Plants and Animals Weathering

See more information in the table below “Examples of Mechanical Weathering”.

Examples of Mechanical Weathering	Weathering Definition
Water Weathering	Water weathering is the process where water will absorb or seep into cracks or crevices of rocks.  Freezing water creates pressure and expansion within the rock.  Thawing creates more room for additional water.
Salt Weathering	Salt weathering is defined by the process of salt water seeping into cracks and crevices.  As the water evaporates the salt will crystalize and grow.  As the crystals grow the host rocks will receive pressure and break apart.
Abrasion and Impact Weathering	Weathering by abrasion and by impact is when friction is caused to break down rocks.  The friction can be from high winds carrying small particles and essentially sand blasting rock.  When rocks come loose, gravity can send that rock down to smash other rocks, breaking them into smaller pieces.
Temperature weathering	Temperature weathering is simply defined as the process in which rocks heat up and cool down.  This heating and cooling repeatedly, causes the rocks to contract and expand.  This will cause the breaking down of rocks.
Exfoliation Weathering	The definition of exfoliation of rocks is the process by which rocks will break off in sheets or pieces.  Pressure from below the rocks can cause the surface rocks to expand, making them weak and crack.  The rocks will shed, or exfoliate pieces of rock.
Plants and Animals Weathering	Weathering by plants and animals is described as organisms causing the breaking down of rocks.  Plants will often sprout roots into the cracks of rocks.  Additionally, moss will attach to the surface of rocks.  In both cases the plants are getting a strong root system, moisture, or nutrients from the rock.  In this though, the host rocks will break down.  Animals above and below the earth will cause the breaking down of rocks through stepping on rocks or breaking up rocks through tunneling.

The Chemical Weathering of Rocks

Chemical weathering of rocks in definition is the process of chemical reactions happening to rocks to cause the breaking down of those rocks.  Chemical reactions from water, carbon dioxide, acids, and even just oxygen can cause reactions to rocks overtime.

Examples of chemical weathering are:

• Weathering by Water
• Acid Weathering
• Weathering from Dead or Living Organisms
• Oxygen Weathering
• Carbon Dioxide Weathering

See more information in the table below “Examples of Chemical Weathering”.

Examples of Chemical Weathering	Weathering Definition
Weathering by Water	Water weathering is a fairly common way of chemical weathering in breaking down rocks.  Water weathering is when water will move and mix elements to create chemical reactions.  Hydration is an example of chemical weathering by water.  This is when water interacts with the minerals within host rock causing chemical reactions and changes.  A great example of a chemical reaction with water and air is when pyrite is involved and creates sulfuric acid.
Acid Weathering	Often nature can produce acids through various elements in the surrounding ecosystem.  Acid weathering is defined as the bringing together of elements to create an acid that causes a chemical reaction.  The rock can either be affected by the created acid or be one of the elemental ingredients to the acid in which the rock will break down.
Weathering from Dead or Living Organisms	Chemical weathering by organisms is defined by those organisms causing chemical reactions to rocks to break them down.  Fungi or simple algae can cause chemical reactions to their host rock by producing acids that help them break down the nutrients within the rock.  Dead animals, or the feces they leave behind, on rocks can cause chemical reactions that will break down rocks.
Oxygen Weathering	The definition of oxygen weathering is when oxygen contributes in the breaking down of rocks.  When iron in rocks mix with oxygen, you get a chemical reaction causing rust.  A similar reaction can be found with a popular mineral called Bornite.
Carbon Dioxide Weathering	Carbon dioxide weathering is when carbon dioxide in the air mixes with water.  This combination will create a mild acid that will dissolve rock.  This can leave large openings in rocks where there might have been greater concentrations of water.

The Biological Weathering of Rocks

Biological weathering involves currently living, or long ago living, organisms that can contribute to mechanical or chemical weathering.  Organisms, alive or dead, will react with rocks and cause the breaking down of those rocks.

This form of weathering is often referred to as a third type of weathering of rocks or minerals.  This is due to the nature of the weathering being in biological form, or in other words plants and animals.

When plants and animals interact in their environment they can cause mechanical or chemical weathering to surrounding rocks and minerals. 

Organisms can weather rocks chemically by their remains and their excrements.  These can cause chemical reactions that will break down rocks.  Organisms can weather rocks mechanically by their penetrating roots, or stomping hoofs, and even their little claws.

There are Different Types of Weathering and There is Erosion

Before I close, I want to describe the difference between the different types of weathering and erosion.  These are often used one in the same but they do carry a difference to be noted.

The differences between weathering and erosion are best described in that weathering is the process of breaking down of rocks.  While erosion is the process of moving, or displacing, those broken down rocks or other materials by water, wind, and other natural forces.