The Formation of Coal Deposits

A look at Coal Deposits in The Lehigh Valley

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Developed and Produced by
The Delaware & Lehigh National Heritage Corridor

Written And Illustrated By
Lance Leonhardt

e-book Publishing software provided by Killer Interactive, LLC.
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Coal's ability to burn has made it one of the most important rocks on Earth. It has lighted fires and provided heat and energy to homes and industries around the world for a thousand years.

Eastern Pennsylvania's Carbon and Luzerne counties are blessed with an underground abundance of anthracite coal, whose high carbon content allows it to burn hotter and longer than other varieties.

Coal was mined in the region in the early 1800s and replaced charcoal as the fuel that stoked the great blast furnaces at iron towns in Carbon, Lehigh, Northampton and Bucks counties.

The abundance of coal and iron and the availability of a cheap immigrant labor force helped the region become an industrial leader and an important player in the birth and growth of the American Industrial Revolution.

Formation of Coal

Coal's ability to burn has made it one of the most important rocks on Earth. It has lighted fires and provided heat and energy to homes and industries around the world for a thousand years.

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Coal is a black sedimentary rock made over millions of years from once-living plant material such as leaves and wood. Tremendous amounts of plant material, and specific conditions and events in Earth’s history, were needed for coal to form.

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Our story of coal begins about 300 million years ago when much of the land that would become the United States was under water. Prehistoric Pennsylvania was located near the equator and was covered by swamps and shallow seas.

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Plants thrived in the tropical climate along the equator where there was an abundance of sunlight, water, and warm temperatures. Swamps along rivers that drained into shallow seas produced huge amounts of plant material over long periods of time.

As the swamp plants died, they became buried and were slowly squeezed, or compressed, into layers of a moist, spongy, partially decayed plant material called peat. The layers of peat settled beneath the swamps and the nearby coastline.

Formation of Coal

Coal is a black sedimentary rock made over millions of years from once-living plant material such as leaves and wood. Tremendous amounts of plant material, and specific conditions and events in Earth’s history, were needed for coal to form.

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United States Three Hundred Million Years Ago
Sea
Land
Pennsylvania
Coastal Swamps and Marshes
River
Delta
Lagoon
Sand Bar
Peat Accumulation
Sand
Mud
Sand
Mud
Compressed Peat
Older Peat Layers
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When trees, ferns, and other swamp plants died, they fell into the shallow swamp water and became buried in the bottom of the swamp where there was little or no oxygen.

The low oxygen levels protected the plant material from decay by decomposers such as bacteria, and allowed the plants to build up in deep layers over time. The layers of plants eventually became layers of peat. The formation of peat is the first step in the process of dead plants becoming coal.

Marine Carbonate Reef

When trees, ferns, and other swamp plants died, they fell into the shallow swamp water and became buried in the bottom of the swamp where there was little or no oxygen.

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Dead Plant Material
Peat
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Tremendous heat and pressure are required to change peat into coal. The heat and pressure in the coal-making process came from the weight of sediments ‐ such as sand and mud ‐ that accumulated on top of the peat layers that laid at the bottom of the swamps.

Sometimes the sand and mud was carried into the swamps by rivers. At other times, rising sea levels carried sand into the swamps. As the swamps became covered with sediments over millions of years, the weight and pressure of the sediments heated and compressed the buried peat layers, squeezing out water and gases from the partly decayed plant material and changing the peat into a type of coal called lignite.

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As compression forced out water and gases in the peat, it concentrated carbon atoms that were used during photosynthesis, a process by which plants make leaves and wood. Materials that contain large amounts of carbon have energy and are combustible, meaning they are able to burn. Wood, for example, is about 50% carbon; peat about 60%. Although coal is a rock, its high levels of carbon allow it to burn.

Coal receives a grade, or rank, by how much carbon it contains. Lignite, with up to 70% carbon, is a low rank coal. Fifty feet of peat compresses into approximately 10 feet of lignite. Compressing lignite further increases the carbon concentration and produces a higher rank coal called bituminous coal, which has a carbon concentration of 75 to 85%. Ten feet of lignite compresses into approximately five feet of bituminous coal.

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A tremendous amount of heat and pressure is required to make anthracite coal, a shiny, hard, black coal that contains up to 98% carbon. Anthracite coal is found in Carbon, Luzerne, and several other eastern Pennsylvania counties.

Layers of Limestone Rock

Tremendous heat and pressure are required to change peat into coal. The heat and pressure in the coal-making process came from the weight of sediments ‐ such as sand and mud ‐ that accumulated on top of the peat layers that laid at the bottom of the swamps.

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Seawater
Sand
Mud
Peat
Lignite
Water & Gas
Peat
60% Carbon
Lignite
70% Carbon
10 Feet Thick
50 Feet Thick
10 Feet Thick
Bituminuous
75 to 85% Carbon
5 Feet Thick
Anthracite
92 to 98% Carbon
5 Feet Thick
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The heat and pressure required to make anthracite coal was provided by a collision of the North American and African continents at the equator some 300 million years ago (according to the plate tectonics theory). The collision lifted, folded, and cracked the Earth's crust upward into mountains. Pennsylvania's Appalachian Mountains were formed at this time.

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The twisting and folding caused by the continental collision produced extremely high amounts of heat and pressure in parts of the Appalachian Mountains, including the mountains in Carbon and Luzerne counties.

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The high heat and pressure from the folding of the Earth's crust compressed bituminous coal layers in these areas into nearly pure-carbon anthracite coal. Anthracite has the highest rank of the three major types of coal, lignite and bituminous being the others. Layers, or seams, of anthracite range from one to 12 feet in thickness. Nearly six billion tons of anthracite coal has been mined in Pennsylvania since 1820.

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Over the last 300 million years, the continents have split apart from the supercontinent Pangaea. Pennsylvania has moved from near the equator (zero degrees latitude) to its current location of 40 degrees latitude. Today, coal formed from ancient, tropical swamp plants over the course of millions of years is burned to generate half of Pennsylvania's electricity.

Lehigh Valley Coal

The heat and pressure required to make anthracite coal was provided by a collision of the North American and African continents at the equator some 300 million years ago (according to the plate tectonics theory). The collision lifted, folded, and cracked the Earth's crust upward into mountains. Pennsylvania's Appalachian Mountains were formed at this time.

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North America
Africa
South America
Equator
Appalachian Mountains
Appalachian Mountains
  • Glossary

    Glossary

    • Sedimentary rock: A layered rock resulting from the packing of sediment (fragments of rock, sand, mud) deposited at the Earth’s surface and into bodies of water by water, wind, or ice.

    • Peat: A deposit of partially decayed dead plant material in a water-filled environment (wetland swamps and bogs). Peat deposits are the earliest stage in the formation of coal. Peat is about 60% carbon.

    • Heat: A form of energy (the motion of molecules of a substance) that can be transferred from one body to another.

    • Lignite: A brownish-black, low-rank coal that forms from peat and with heat and pressure can become bituminous coal. Lignite is up to 70% carbon.

    • Carbon: A very common nonmetallic element which occurs in combination with other elements in all plants and animals. The atoms of carbon can link with one another into rings and chains to form molecules like those in coal, that when burned, release large amounts of energy.

    • Photosynthesis: The process by which plant cells make high-energy carbon compounds (like sugar) by combining carbon dioxide and water using sunlight energy, and releasing oxygen. It is the energy in the carbon compounds made by ancient plants using photosynthesis that is released as heat energy when coal is burned.

    • Combustion: Chemical reactions during the burning of a fuel (like coal) in the presence of oxygen that release heat and light energy.

    • Rank: The rank of coal is generally based on its carbon content. Lignite (up to 70% carbon) is a low rank coal. Bituminous coal (75 to 85% carbon) is higher in rank. Anthracite (up to 98% carbon) is the highest ranked and cleanest burning coal.

    • Bituminous coal: A black, relatively soft coal formed from lignite. Bituminous coal is around 75 to 85% carbon.

    • Anthracite coal: A hard, black, shiny coal formed from bituminous coal. Anthracite has the highest amount of carbon (up to 98%) of the 3 general types of coal and the fewest impurities, and so is the cleanest burning coal.

    • Plate tectonics theory: Plate tectonics is a scientific theory that describes the large scale movements of the Earth's crust over time. The Earth’s crust is broken into sections or tectonic plates that ride on and are moved by flowing, liquid-like rock in a layer below the crust called the asthenosphere. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur where the plates meet along tectonic plate boundaries.

    • Earth’s crust: The outermost, rocky layer of the Earth. The crust of the Earth is composed of a great variety of igneous, metamorphic, and sedimentary rocks.

    • Appalachian Mountains: The Appalachian Mountains are a system of mountains in eastern North America that were formed around 325 million to 260 million years ago during continental plate collisions of Africa and North America.

    • Supercontinent Pangaea: A supercontinent (a large landmass made up of many continents joined together) that formed about 300 million years ago and began to break apart approximately 200 million years ago.

    • Electricity: Energy generated by the presence and flow of charged particles. A flow or movement of electrically charged particles can generate energy over time or electrical power. Coal is burned to produce the heat to boil water into steam that drives the turbines used in generating the electrical power used to run air conditioners, refrigerators, heaters, computers, light bulbs, toys, and cars.

  • CC

    Lesson Text

  • Standards

    Pennsylvania Academic Standards

    7.1. Geography

    7.1.4.B.
    Describe and locate places and regions s defined by physical and human features.

    Geography Glossary

    Place – an area with distinctive human and physical characteristics; these characteristics give it meaning and character and distinguish it from other areas.

    Region – an area with one or more common characteristics or features that gives it a measure of consistency and makes it different from surrounding areas.

    3.2. Physical Sciences: Chemistry and Physics

    3.2.4.A4.
    Recognize that combining two or more substances may make new materials with different properties.

    3.3. Earth and Space Sciences

    3.3.4.A1.
    Describe basic landforms.

    Recognize that the surface of the earth changes due to slow processes and rapid processes.

    3.3.4.A2.
    Identify basic properties and uses of Earth’s materials including rocks, soils, water and gases of the atmosphere.

    3.3.5.A2.
    Describe the usefulness of Earth’s physical resources as raw materials for the human made world.

    3.3.4.A3.
    Recognize that fossils provide evidence about the plants and animals that lived long ago and the nature of the environment at that time.

    3.3.4.A4.
    Recognize Earth’s different water resources, including both fresh and saltwater.

    3.3.4.A6.
    CONSTANCY/CHANGE – Identify simple changes in the earth system as air, water, soil and rock interact.

    Earth and Space Sciences Glossary

    Atmosphere – the gaseous mass or envelope surrounding a celestial body, especially the one surrounding the Earth, and retained by the celestial body’s gravitational field.

    System – a set of interacting or interdependent entities, real or abstract, forming an integrated whole. An open system usually interacts with some entities in their environment. A closed system is isolated from its environment.

    4.3. Environment and Ecology

    4.3.4.A.
    Identify ways humans depend on natural resources for survival.

    Identify resources used to provide humans with energy, food, employment, housing and water.

    4.3.4.B.
    Identify the geographic origins of various natural resources.

    Environment and Ecology Glossary

    Natural resources – any materials produced by nature that can be used to produce goods or provide services.

  • My Map

    • Magnetite & Hematite ore Deposits
    • Limonite ore Deposits
    • Anthracite Coal Deposits
    • Slate Deposits
    • Surface Carbonate Rock Deposits
      (Limestone and/or Dolomite)
    • Limestone mined for cement
      (manufacture & cement plants)
    • Geography
    • Water
    • Counties
    • Cities
    Magnetite & Hematite ore Deposits
    Limonite ore Deposits
    Anthracite Coal Deposits
    Slate Deposits
    Surface Carbonate Rock Deposits
    (Limestone and/or Dolomite)
    Limestone mined for cement
    (manufacture & cement plants)
    Geography
    Water
    Counties
    County Names
    City Names

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