Katerina Swanson
Coal is a non-renewable fossil fuel formed from the remains of plants that lived millions of years ago. Over time, layers of dirt and rock built up over these plants, subjecting them to extreme heat and pressure, eventually transforming them into coal seams or beds. Coal is a combustible sedimentary rock with a high carbon content, and its ranking is determined by the amount of carbon it contains and the heat energy it can produce. The burning of coal releases carbon dioxide, a greenhouse gas, contributing to climate change.
| Characteristics | Values |
|---|---|
| Definition | Coal is a combustible black or brownish-black sedimentary rock with a high amount of carbon and hydrocarbons |
| Formation | Coal contains the energy stored by plants that lived hundreds of millions of years ago in swampy forests. Layers of dirt, rock, mud, and acidic water covered the plants over millions of years, preventing contact with oxygen and slowly turning the plants into coal through a process called carbonization |
| Fossilization | Paleontologists have discovered brilliantly preserved fossils of some of the world's oldest tropical rainforests in coal seams |
| Classification | Coal is classified as a nonrenewable fossil fuel because it takes millions of years to form. It is ranked into four main types: anthracite, bituminous, subbituminous, and lignite, based on carbon content and heat energy potential |
| Carbon Content | Anthracite contains 86%-97% carbon, bituminous coal 45%-86% carbon, subbituminous coal 35%-45% carbon, and lignite 25%-35% carbon |
| Usage | Coal is combusted to generate electricity and is used as a raw material in the iron and steel industry. Byproducts are used to make synthetic materials such as tar, fertilizers, and plastics |
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What You'll Learn
Coal is a sedimentary rock with a high carbon content
Coal is a combustible black or brownish-black sedimentary rock with a high carbon content. It is classified as a non-renewable energy source because it takes millions of years to form. Coal is formed from the energy stored by plants that lived hundreds of millions of years ago in swampy forests. Over time, layers of dirt and rock covered these plants, and the resulting pressure and heat turned them into coal. The process of converting dead vegetation into coal is called coalification.
During the coalification process, the complex organic compounds that make up plant material, such as cellulose, lignin, fats, waxes, and tannins, are broken down and new compounds are produced. The type of compounds produced depends on the amount of heat and pressure that acted on the plants over time. Coal with a higher rank, such as anthracite, has a higher carbon content and can produce more heat energy.
The formation of coal began when dead plant matter in wetlands was protected from oxidation, usually by mud or acidic water, and was converted into peat. Peat bogs trap large amounts of carbon and, over time, were deeply buried by sediments. The heat and pressure of deep burial caused the loss of water, methane, and carbon dioxide, increasing the proportion of carbon. This process of coalification can take millions of years, and the resulting coal can be between 100 and 300 million years old, as is the case with bituminous coal in the United States.
The ranking of coal depends on the types and amounts of carbon it contains, as well as the amount of heat energy it can produce. Anthracite, the highest rank of coal, contains between 86% and 97% carbon and is used primarily for residential and commercial space heating. Bituminous coal, the most abundant rank in the United States, contains between 45% and 86% carbon and is used for electricity generation and making coking coal for the iron and steel industry. Subbituminous coal typically contains 35%–45% carbon and has a lower heating value than bituminous coal. Lignite, the lowest rank of coal, contains 25%–35% carbon and has the lowest energy content.
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It takes millions of years for coal to form
Coal is a non-renewable fossil fuel that takes millions of years to form. It is a sedimentary rock with a high carbon and hydrocarbon content. The formation of coal began millions of years ago in swampy forests, where layers of dirt and rock covered plants, preventing them from coming into contact with oxygen. Over time, the heat and pressure from these layers caused the plants to decompose slowly, retaining most of their carbon content. This carbon is what gives coal its energy value.
The process of coal formation, or carbonization, involves the compression of layered vegetation under extreme heat and pressure. This process transforms the organic material into the substance we call coal. The amount of pressure and heat acting on the plants over time determines the rank of the resulting coal deposit. Coal is classified into four main types: anthracite, bituminous, subbituminous, and lignite.
Anthracite, the highest-ranking coal, contains the highest proportion of carbon, ranging from 86% to 97%. It also has the highest heating value of all coal types. Bituminous coal, the second-highest ranking, contains 45% to 86% carbon and is the most abundant type of coal in the United States. Subbituminous coal, with a carbon content of 35% to 45%, has a lower heating value than bituminous coal.
Lignite coal deposits are relatively young and have not been subjected to the same extreme heat and pressure as higher-rank coals. They contain between 25% and 35% carbon and have the lowest energy content of all coal types. The ranking of coal deposits is crucial, as it determines their suitability for various industrial applications, such as electricity generation and steel production.
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Coal is formed from the remains of ancient plants
Coal is a non-renewable fossil fuel formed from the remains of ancient plants. It is a combustible black or brownish-black sedimentary rock with a high amount of carbon and hydrocarbons. Coal is formed over millions of years when layers of dirt and rock cover plants, applying pressure and heat, turning them into coal. This process is known as carbonization, which takes place under extreme heat and pressure.
The ancient plants that became coal lived in swampy forests, and the conditions of their decomposition led to the formation of coal seams or coal beds. These seams can be up to 30 meters thick and stretch for hundreds of kilometers. Coal seams are layers of coal found underground, and they are the result of the compression and transformation of plant matter over millions of years.
The process of coal formation starts with the burial of plant matter in peat bogs, where mud and acidic water prevent contact with oxygen. This environment causes the plant matter to decompose slowly, retaining most of its carbon. Over time, the heat and pressure increase, and the peat transforms into coal through carbonization.
The ranking of coal depends on the types and amounts of carbon it contains, as well as the amount of energy it can produce. Anthracite, with the highest carbon content, has the greatest heating value, while lignite, with lower carbon content, has a lower energy value. The age and formation conditions of coal deposits also contribute to their ranking.
Coal is a significant energy source, providing about half of the electricity generation in the United States. It is used for electricity production, as well as a raw material in industries such as iron and steel production. However, the combustion of coal releases harmful gases and particulates, impacting the environment and contributing to climate change.
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Peat bogs are a key part of the process
Peat bogs are areas of buried plant matter that formed in swampy forests. The mud and acidic water in these environments prevented the plant matter from coming into contact with oxygen, allowing it to decompose slowly and retain most of its carbon. Peat bogs store massive amounts of carbon several meters underground, and peat itself can be burned as a fuel source.
Under specific conditions, peat undergoes a process called carbonization, transforming into coal. Carbonization occurs under intense heat and pressure, causing the peat to compress into coal. This process can reduce a three-meter layer of vegetation to a third of a meter of coal.
Coal exists in underground formations called "coal seams" or "coal beds," which can be up to 30 meters thick and stretch for hundreds of kilometers. The ranking of coal, which includes anthracite, bituminous, subbituminous, and lignite, depends on the carbon types and amounts, as well as the heat energy it can produce. The rank of a coal deposit is influenced by the pressure and heat it was subjected to over time.
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Coal is categorised into four types
Coal is a combustible black or brownish-black sedimentary rock with a high amount of carbon and hydrocarbons. It is classified as a non-renewable energy source because it takes millions of years to form. Coal contains the energy stored by plants that lived hundreds of millions of years ago in swampy forests. Layers of dirt and rock covered the plants over millions of years. The resulting pressure and heat turned the plants into coal. This process is called coalification.
Anthracite
Anthracite is the highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as "hard coal". Anthracite contains 86%–97% carbon and generally has the highest heating value of all ranks of coal. It is mainly used by the metals industry. In 2022, anthracite accounted for less than 1% of the coal mined in the United States, with all mines located in northeastern Pennsylvania.
Bituminous
Bituminous coal is the second-highest rank of coal and is the most abundant type found in the United States. It usually has a high heating value and is used in electricity generation and steelmaking. Bituminous coal contains 45%–86% carbon. In 2022, it accounted for about 46% of total U.S. coal production.
Subbituminous
Subbituminous coal is the third-highest rank of coal. It is black in colour and is mainly dull, not shiny. Subbituminous coal typically contains 35%–45% carbon and has a lower heating value than bituminous coal. Most subbituminous coal in the United States is at least 100 million years old. In 2022, subbituminous coal accounted for about 46% of total U.S. coal production.
Lignite
Lignite, also known as brown coal, is the lowest grade of coal with the least concentration of carbon. It contains 25%–35% carbon and has the lowest energy content of all coal ranks. Lignite has a low heating value and a high moisture content, contributing to its low heating value. Lignite coal deposits tend to be relatively young and were not subjected to extreme heat or pressure. In 2022, five states produced lignite, which accounted for 8% of total U.S. coal production.
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Frequently asked questions
Coal is a nonrenewable fossil fuel that is combustible and used to generate electricity.
Coal contains the energy stored by plants that lived hundreds of millions of years ago in swampy forests. Layers of dirt, rock, mud, and acidic water covered the plants over millions of years. The resulting pressure and heat turned the plants into the substance we now call coal.
Coal takes millions of years to form. For example, most subbituminous coal in the United States is at least 100 million years old.
Coal is a sedimentary rock with a high amount of carbon and hydrocarbons. The amount of carbon in coal can vary between 25% and 97%, depending on the type of coal.
