Which One of the Following Is Not Related to Chemical Weathering? A Guide to Understanding the Process of Rock Decay

Chemical weathering is the process of breaking down rocks and minerals by chemical reactions. It is one of the main agents of erosion, along with physical weathering and biological weathering. Chemical weathering can change the composition, color, texture and shape of rocks, making them more susceptible to further weathering and erosion. In this article, we will explore the four main types of chemical weathering, their examples and effects, and how to identify which one of the following is not related to chemical weathering.

What Is Chemical Weathering?

According to ThoughtCo, chemical weathering, also known as decomposition or decay, is the breakdown of rock by chemical mechanisms. It does not break rocks into smaller fragments by wind, water or ice (that’s physical weathering), nor does it break rocks apart by the action of plants or animals (that’s biological weathering). Instead, it changes the chemical composition of the rock, usually through carbonation, hydration, hydrolysis or oxidation.

Chemical weathering alters the composition of the rock material toward surface minerals, such as clays. It attacks minerals that are relatively unstable in surface conditions, such as the primary minerals of igneous rocks like basalt, granite or peridotite. It can also occur in sedimentary and metamorphic rocks and is an element of corrosion or chemical erosion.

Water is especially effective at introducing chemically active agents by way of fractures and causing rocks to crumble piecemeal. Water may also loosen thin shells of material (in spheroidal weathering). Chemical weathering may include shallow, low-temperature alteration.

Types and Examples of Chemical Weathering

There are four main types of chemical weathering that are commonly recognized: carbonation, hydration, hydrolysis and oxidation. These are not the only forms, just the most common. Let’s take a look at each one in detail.


Carbonation occurs when rain, which is naturally slightly acidic due to atmospheric carbon dioxide (CO2), combines with a calcium carbonate (CaCO3), such as limestone or chalk. The interaction forms calcium bicarbonate, or Ca(HCO3)2. Rain has a normal pH level of 5.0-5.5, which alone is acidic enough to cause a chemical reaction. Acid rain, which is unnaturally acidic from atmospheric pollution, has a pH level of 4 (a lower number indicates greater acidity while a higher number indicates greater basicity).

Carbonation, sometimes referred to as dissolution, is the driving force behind the sinkholes, caverns and underground rivers of karst topography. Karst topography is a landscape characterized by features formed by the dissolution of soluble rocks such as limestone, dolomite and gypsum. Carbonation can also dissolve marble statues and buildings over time.


Hydration occurs when water reacts with an anhydrous mineral, creating a new mineral. The water is added to the crystalline structure of a mineral, which forms a hydrate. Anhydrite, which means “waterless stone,” is a calcium sulfate (CaSO4) that is usually found in underground settings. When exposed to water near the surface, it quickly becomes gypsum, the softest mineral on the Mohs hardness scale.

Hydration can also affect clay minerals, such as kaolinite and montmorillonite. These minerals can absorb water molecules between their layers, causing them to expand and contract with changes in humidity. This can weaken the cohesion of rocks that contain these minerals and make them more prone to erosion.


Hydrolysis is the opposite of hydration; in this case, water breaks down the chemical bonds of a mineral instead of creating a new mineral. It is a decomposition reaction. The name makes this one particularly easy to remember: The prefix “hydro-” means water, while the suffix “-lysis” means decomposition, breakdown or separation.

Hydrolysis occurs when water comes in contact with minerals that contain silicate ions (SiO4), such as feldspar, quartz and mica. The water molecules split into hydrogen ions (H+) and hydroxide ions (OH-). The hydrogen ions replace some of the metal ions in the silicate minerals, forming new minerals such as clay and releasing soluble ions such as potassium (K+), sodium (Na+), calcium (Ca2+) and magnesium (Mg2+).

Hydrolysis can change the color and texture of rocks. For example, when granite reacts with water, feldspar crystals inside the granite turn into clay minerals. The clay weakens the rock, making it more likely to break. The clay also gives granite a reddish or brownish hue.


Oxidation occurs when oxygen reacts with a mineral, changing its chemical composition and forming an oxide. Oxidation is also known as rusting or tarnishing. It is a type of redox reaction, which involves the transfer of electrons between atoms.

Oxidation affects minerals that contain iron (Fe), such as pyrite, magnetite and hematite. When these minerals are exposed to oxygen and water, they lose electrons and form iron oxides, such as hematite (Fe2O3) and goethite (FeO(OH)). These iron oxides have a reddish or yellowish color, which gives rocks a rusty appearance.

Oxidation can also affect copper (Cu), silver (Ag) and other metals. For example, when copper reacts with oxygen and water, it forms copper carbonate (CuCO3), which has a greenish color. This is why the Statue of Liberty, which is made of copper, has a green patina.

Now that we have learned about the four main types of chemical weathering, we can answer the question: Which one of the following is not related to chemical weathering?

  • A) Frost wedging
  • B) Carbonation
  • C) Hydration
  • D) Oxidation

The correct answer is A) Frost wedging. Frost wedging is a type of physical weathering, not chemical weathering. It occurs when water freezes in cracks and crevices in rocks, expanding and exerting pressure on the surrounding rock. This can cause the rock to split or fracture along the cracks.

The other three options are all related to chemical weathering. Carbonation is the reaction of rainwater with calcium carbonate minerals, forming calcium bicarbonate. Hydration is the reaction of water with anhydrous minerals, forming hydrates. Oxidation is the reaction of oxygen with metal minerals, forming oxides.


Chemical weathering is an important process that shapes the Earth’s surface and contributes to soil formation. It can change the composition, color, texture and shape of rocks by altering their chemical structure. There are four main types of chemical weathering: carbonation, hydration, hydrolysis and oxidation. Each one has its own examples and effects on different types of rocks and minerals.

To identify which one of the following is not related to chemical weathering, we need to know the difference between chemical weathering and physical weathering. Physical weathering breaks down rocks into smaller fragments by mechanical forces, such as wind, water, ice, plants and animals. Chemical weathering breaks down rocks by chemical reactions, such as acid-base reactions, redox reactions and decomposition reactions.

We hope this article has helped you understand the process of chemical weathering and how to answer the question: Which one of the following is not related to chemical weathering?

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