Is Coal a Mineral? (+ 3 Things to Know)

No, coal is not considered a mineral. It is classified as a sedimentary rock composed of organic matter, primarily plant material, and does not meet the criteria of a mineral, which typically consists of inorganic substances with a definite chemical composition and crystalline structure. ¹

Well, this was just a simple answer. But there are few more things to know about this topic which will make your concept super clear.

So let’s dive right into it.

Why is coal not a mineral?

Coal is not considered a mineral because it is an organic substance formed from the remains of plants and other organic matter. ^{2 3} While minerals are naturally occurring inorganic substances with a specific chemical composition and crystal structure, coal is primarily composed of carbon, along with various other elements such as hydrogen, oxygen, nitrogen, and sulfur.

Coal is formed through a geological process called coalification, which involves the transformation of plant materials under high temperature and pressure over millions of years. ^{4 5}

This process results in the formation of different types of coal, such as lignite, sub-bituminous coal, bituminous coal, and anthracite, each with varying carbon content and energy potential.

While coal deposits are often found alongside minerals in the Earth’s crust, the distinction between minerals and coal lies in their composition and origin.

Minerals, such as quartz, feldspar, or calcite, are inorganic substances that crystallize naturally, whereas coal is derived from organic matter and lacks a crystalline structure. Therefore, coal is classified as a sedimentary rock rather than a mineral.

How is coal different from minerals?

Coal is different from minerals in several key ways:

• Composition: Coal is primarily composed of carbon, along with varying amounts of other elements such as hydrogen, oxygen, nitrogen, and sulfur. ⁶ Minerals, on the other hand, are inorganic substances with a specific chemical composition and crystal structure. They are made up of elements or compounds arranged in a specific repeating pattern.
• Formation: Coal is formed from the remains of plants and other organic matter that undergo a process called coalification. ⁷ This process involves the burial and decomposition of organic materials under high temperature and pressure over millions of years. Minerals, on the other hand, are formed through geological processes such as crystallization from magma, precipitation from water, or deposition from mineral-rich solutions.
• Properties: Coal is a combustible material and is primarily used as a fossil fuel for energy generation. ⁸ It has a relatively low density, is brittle, and burns when exposed to heat. Minerals, on the other hand, exhibit a wide range of physical and chemical properties depending on their composition. They can be transparent or opaque, have various hardness levels, exhibit different colors, and have distinct crystal structures.
• Classification: Coal is classified as a sedimentary rock, specifically a combustible black or brownish-black sedimentary rock. It is categorized into different types based on its carbon content and energy potential, such as lignite, sub-bituminous coal, bituminous coal, and anthracite. Minerals, on the other hand, are classified based on their chemical composition, crystal structure, and physical properties into various mineral groups and species. ⁹

While coal deposits are often found in association with minerals in the Earth’s crust, they are distinct from minerals due to their organic origin, composition, and formation processes.

How is coal formed?

Coal is formed through a process called coalification, which involves the transformation of plant materials over millions of years. As plants and organic matter accumulate and are buried in swampy environments, they undergo physical and chemical changes due to heat and pressure, eventually resulting in the formation of coal. ¹⁰

During the coal formation process, dead plants and organic matter accumulate in swamps and wetland environments. Over time, layers of sediment build up and bury the plant materials. As the layers of sediment increase, the weight of the overlying sediments exerts pressure on the lower layers. This pressure, combined with heat from the Earth’s interior, initiates the process of coalification.

The heat and pressure cause physical and chemical changes in the buried plant matter. The initial stage of coalification is the formation of peat, a brown, soft material with a high moisture content. As more sediment accumulates and the burial continues, the peat undergoes compaction and loses moisture, transforming into lignite, a low-grade coal.

Further burial and increased heat and pressure cause the lignite to undergo additional changes. It becomes more compact, loses more moisture, and progresses to become sub-bituminous coal, bituminous coal, and ultimately, anthracite, which is the highest grade of coal with the highest carbon content and energy potential.

The specific type of coal formed depends on factors such as the types of plants involved, the amount of heat and pressure, and the duration of the coalification process. ¹¹ The entire process of coal formation, from plant material to coal, can take millions of years.

Further reading

Is Oil a Mineral?
Is Salt a Mineral?
Is Water a Mineral?
Is Glass a Mineral?
Is Mercury a Mineral?

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