Table of Contents
Quick Facts About Coal
Coal has shaped the modern world in ways most people never think about. Here are some of the most interesting things about this ancient energy source.
Coal is millions of years old. Most of the coal we burn today formed 300–360 million years ago during the Carboniferous Period, when giant ferns and swampy forests covered much of the Earth.
Coal once generated over half of all U.S. electricity. In 2005, coal produced about 50% of America’s power. By 2024, that had dropped to around 16% as natural gas and renewables took over.
Coal is the most abundant fossil fuel on Earth. There’s more coal underground than oil and natural gas combined. The world has enough known coal reserves to last over 100 years at current usage rates.
The Romans traded coal nearly 2,000 years ago. Archaeological evidence shows the Roman Empire mined and traded coal in Britain as early as the 2nd century AD.
Wyoming mines more coal than any other U.S. state — by a huge margin. Wyoming alone produces about 40% of all the coal mined in the entire country.
Coal is made from ancient plants. The energy stored in coal originally came from the sun — captured by plants through photosynthesis hundreds of millions of years ago and preserved underground.
What is Coal?
Coal is a black or dark brown rock that you can burn to release energy as heat. It belongs to a group of energy sources called fossil fuels, which also includes oil and natural gas. Fossil fuels are called “fossil” fuels because they formed from the remains of living things that died a very long time ago.
Coal’s story begins hundreds of millions of years ago, during a time called the Carboniferous Period (about 300–360 million years ago). Back then, much of the Earth was covered in hot, steamy swamps filled with giant ferns, mosses, and trees. When these plants died, they fell into the swamp water. Normally, dead plants decompose (break down), but the swamp water had very little oxygen, so the plants didn’t fully decay. Instead, they piled up in thick layers.
Over millions of years, sand, clay, and other sediments buried these layers deeper and deeper underground. The weight of everything above created enormous pressure, and the Earth’s internal warmth added heat. Together, that pressure and heat slowly transformed the spongy plant material into the hard, carbon-rich rock we call coal.
The energy inside a lump of coal is really ancient solar energy. Those prehistoric plants captured sunlight through photosynthesis and stored it as chemical energy. When we burn coal, we’re releasing sunshine that’s been locked underground for over 300 million years!
The Four Types of Coal
Not all coal is the same. Coal is ranked by how much carbon it contains and how much heat energy it can produce when burned. The longer coal has been underground (and the more heat and pressure it has experienced), the higher its rank. There are four types, from lowest to highest energy.
Lignite
The youngest and softest coal. It’s brownish-black, crumbly, and contains a lot of moisture. Lignite produces the least heat of any coal type. It’s mainly used in power plants located near the mines where it’s found, since it’s not efficient to transport long distances.
Subbituminous
A step up from lignite. It’s darker, harder, and contains less moisture. Subbituminous coal is about 100 million years old and is the most commonly mined coal in the U.S., with most of it coming from Wyoming’s Powder River Basin.
Bituminous
The most widely used coal worldwide. It’s 100–300 million years old, dense, and black. Bituminous coal produces a lot of heat and is used for both electricity generation and making steel. Most coal mined in the eastern U.S. is bituminous.
Anthracite
The oldest, hardest, and highest-energy coal. Anthracite is shiny, jet-black, and burns very hot with little smoke. It’s rare — less than 1% of the coal mined in the U.S. is anthracite. Most of it is found in northeastern Pennsylvania.
Imagine coal types on a scale: on one end is lignite (soft, young, low energy) and on the other end is anthracite (hard, ancient, high energy). The more heat and pressure the coal experienced over millions of years, the further along the scale it moves — and the more energy it packs.
How Coal Generates Electricity
Coal doesn’t make electricity on its own. It has to go through several steps inside a coal-fired power plant. Here’s how the process works, step by step.
Mining & Delivery
Coal is mined from the ground and transported to a power plant, usually by train. Some power plants receive multiple trainloads of coal every single day.
Crushing
At the plant, the coal is crushed into a fine powder — almost as fine as talcum powder. This helps it burn faster and more completely.
Burning
The powdered coal is blown into a giant furnace called a boiler, where it burns at extremely high temperatures — over 2,500°F (1,400°C).
Making Steam
The heat from the burning coal boils water inside tubes that line the boiler walls. The water turns into high-pressure steam.
Spinning the Turbine
The steam shoots through a massive turbine, making its blades spin at up to 3,600 revolutions per minute. The turbine is connected to a generator.
Generating Electricity
The spinning turbine drives the generator, which converts the mechanical energy into electrical current. This is the same basic principle Michael Faraday discovered in 1831.
Transmission
The electricity flows into a transformer that boosts the voltage, then travels through high-voltage transmission lines to cities and towns, and eventually to your home.
A large coal power plant can burn over 10,000 tons of coal per day — that’s roughly the weight of 80 blue whales. A single plant can generate enough electricity to power more than 500,000 homes.
How Coal is Mined
Before coal can generate electricity, it has to be dug out of the ground. This process is called mining, and the people who do it are called miners. There are two main methods, and which one is used depends on how deep the coal is buried.
Surface Mining
When coal is less than about 200 feet underground, miners use enormous machines — excavators, bulldozers, and dump trucks — to remove the soil and rock on top (called overburden) and expose the coal beneath. Sometimes explosives are used to break through rock. After the coal is collected, the mining company is required by law to fill the area back in with soil and replant trees and vegetation. Surface mining is cheaper and safer than underground mining, but it dramatically changes the landscape.
Underground Mining
When coal is buried deep underground — sometimes more than 1,000 feet down — miners dig shafts and tunnels to reach it. They ride elevators down into the mine and use small rail cars to travel through tunnels. Giant machines called continuous miners and longwall miners cut the coal from the seam. Underground mining is more dangerous due to risks like cave-ins, gas explosions, and coal dust. Modern mines use advanced ventilation and safety systems to protect workers.
The world’s largest dump trucks, used in surface coal mines, can carry over 400 tons in a single load. Their tires alone are over 13 feet tall — more than twice the height of most adults!
Coal in the United States
The United States has some of the largest coal reserves in the world. Coal has played an enormous role in American history, powering the Industrial Revolution, railroads, and the rise of electric power. Today, coal is used for three main purposes.
How Coal is Used
Electric Power
The vast majority of coal is burned in power plants to generate electricity. Coal-fired plants still supply about 16% of U.S. electricity, though this number continues to decline each year as natural gas and renewables grow.
Steel & Industry
A special type of coal called metallurgical coal (or “coking coal”) is heated to make coke, a key ingredient in producing steel. Steel is used to build bridges, skyscrapers, cars, and appliances.
Other Products
Coal by-products are used to make things you might not expect: activated carbon (for water filters), certain plastics, medicines, and even the carbon fiber used in sports equipment and aircraft.
Top Coal-Producing States
Coal is found in many parts of the country, but five states produce the lion’s share.
- Wyoming — produces about 40% of all U.S. coal, mostly from enormous surface mines in the Powder River Basin
- West Virginia — the historic heart of American coal mining, with both surface and underground mines
- Pennsylvania — home to nearly all U.S. anthracite deposits and a long mining heritage
- Illinois — large bituminous coal reserves in the Illinois Basin
- Kentucky — significant mining in both the eastern mountains and the western coalfields
In 2005, coal generated about 50% of all U.S. electricity. By 2024, that number had fallen to roughly 16%. Natural gas became the top source around 2016, and renewable energy (wind, solar, and hydro) has been growing rapidly ever since. Many coal plants have closed or been converted to run on natural gas.
Coal and the Environment
Coal is a powerful source of energy, but burning it and mining it cause significant environmental problems. Understanding these impacts is an important part of learning about energy.
Air Pollution
When coal burns, it releases several pollutants into the air:
- Carbon dioxide (CO₂) — a greenhouse gas that traps heat in the atmosphere and contributes to climate change. Coal produces more CO₂ per unit of energy than any other fuel.
- Sulfur dioxide (SO₂) — combines with moisture in the atmosphere to form acid rain, which can harm forests, lakes, and buildings.
- Nitrogen oxides (NOx) — contribute to smog and respiratory health problems.
- Particulate matter — tiny particles that can get deep into your lungs and cause health issues.
- Mercury — a toxic heavy metal released in small amounts that can accumulate in fish and waterways.
Mining Impacts
Surface mining removes entire mountaintops and forests to reach coal underneath. This destroys habitats, pollutes streams, and permanently changes the landscape. Underground mining can cause land to sink (called subsidence) and produces wastewater that must be carefully managed.
What’s Being Done
Over the decades, the U.S. government has passed laws to reduce coal’s environmental damage:
- The Clean Air Act requires power plants to install scrubbers and filters that capture pollutants before they leave the smokestack.
- The Surface Mining Control and Reclamation Act requires mining companies to restore the land after mining is complete.
- Many older, dirtier coal plants have been retired and replaced with cleaner natural gas or renewable energy.
Coal is the single largest source of carbon dioxide emissions from electricity generation worldwide. Reducing coal use is considered one of the most important steps in fighting climate change, which is why many countries are working to replace coal with wind, solar, and other clean energy sources.
Pros and Cons of Coal
Like every energy source, coal has both advantages and disadvantages. Here’s a balanced look at both sides.
- Abundant. There is more coal on Earth than any other fossil fuel. Known reserves could last over 100 years.
- Reliable. Coal plants can run around the clock regardless of weather, unlike solar and wind which depend on sunshine and wind.
- Affordable. Coal has historically been one of the cheapest fuels for generating electricity.
- Established infrastructure. Decades of investment mean coal has extensive mining, rail, and power plant systems already built.
- Versatile. Besides electricity, coal is essential for making steel and can be converted into liquid fuels or gas.
- Biggest carbon emitter. Coal releases more CO₂ per unit of energy than any other fuel, making it a major driver of climate change.
- Air & water pollution. Burning coal releases sulfur dioxide, mercury, and particulates that harm health and the environment.
- Non-renewable. Once burned, coal is gone forever. It takes millions of years to form again.
- Mining harms the land. Surface mining destroys mountains, forests, and streams. Underground mining poses dangers to workers.
- Becoming more expensive. As natural gas and renewables get cheaper, coal is losing its cost advantage in many markets.
History of Coal
Coal has been part of human history for thousands of years. From ancient hearths to the factories of the Industrial Revolution and the power plants of today, here are the key moments in coal’s story.
The Roman Empire mined coal in Britain and used it for heating. Archaeologists have found coal ash at Roman forts and settlements across England.
Coal became widely used in England as forests were cut down and firewood became scarce. London’s air grew so smoky from coal fires that King Edward I briefly banned coal burning in 1306.
Thomas Newcomen built the first practical steam engine, powered by coal. It was used to pump water out of coal mines, allowing miners to dig deeper than ever before.
The Industrial Revolution transformed the world, with coal at its center. Coal-powered steam engines ran factories, locomotives, and ships, driving the biggest economic shift in human history.
Thomas Edison opened the Pearl Street Station in New York City — one of the first commercial power plants. It burned coal to generate electricity for 85 customers in lower Manhattan.
Coal powered nearly everything: trains, ships, factories, and home heating. At its peak, the U.S. employed over 800,000 coal miners.
The Clean Air Act was signed into law, beginning a decades-long effort to reduce the pollution from burning coal. Power plants were required to install scrubbers and filters.
Coal reached its modern peak, generating about 50% of U.S. electricity. After this point, cheap natural gas from the fracking boom began displacing coal rapidly.
Natural gas surpassed coal as the #1 source of U.S. electricity for the first time. Coal’s share continued to decline each year as gas prices stayed low and renewables grew.
Renewable energy generated more electricity than coal in the U.S. for the first time. Coal’s share had fallen to about 16%, and hundreds of coal plants across the country had closed.
The shift away from coal continues worldwide. Many countries have set coal phase-out dates, and investment in wind, solar, and battery storage is at an all-time high. Coal’s role in electricity is smaller than at any point in the last century.
Coal Vocabulary
These are key terms that will help you understand coal and how it fits into the world of energy.
The highest rank of coal. It’s very hard, shiny, and produces the most heat when burned. Anthracite is rare and found mainly in Pennsylvania.
The most common type of coal used worldwide. It’s dense and black, and is burned for electricity and used to make steel.
A huge furnace in a power plant where coal is burned to heat water into steam. The boiler is the first major step in turning coal into electricity.
A greenhouse gas released when coal (and other fossil fuels) are burned. It traps heat in the atmosphere and is a primary driver of climate change.
A geological era roughly 300–360 million years ago when vast swampy forests covered the Earth. Most of the world’s coal deposits formed from plants that lived during this time.
A hard, carbon-rich material made by heating coal without air. Coke is a critical ingredient in steelmaking.
An energy source formed from the remains of ancient plants and animals. Coal, oil, and natural gas are all fossil fuels. They are non-renewable.
A machine that converts spinning motion into electricity. In a coal plant, the turbine spins the generator to produce electrical current.
The lowest-ranking type of coal. It’s soft, brownish, and contains a lot of moisture. Lignite produces the least energy when burned.
An energy source that exists in a limited supply and cannot be replaced in a human lifetime. Coal, oil, and natural gas are all non-renewable.
The layers of soil and rock that sit on top of a coal seam. In surface mining, the overburden must be removed before coal can be extracted.
The process of restoring land after mining. Mining companies are required by law to fill in mined areas, replace soil, and replant vegetation.
A device installed in coal plant smokestacks that removes sulfur dioxide and other pollutants from the exhaust before it enters the atmosphere.
A mid-ranking coal that’s harder than lignite but softer than bituminous. It’s the most commonly mined coal in the U.S., mostly from Wyoming.
A machine with blades that spin when pushed by steam, water, or wind. In a coal plant, high-pressure steam drives the turbine to produce electricity.
Keep Exploring Energy for Kids
Now that you know about coal, explore our full guide to electricity — covering solar, wind, EVs, lightning, and more.
Electricity for Kids