So yes, coal is classified as an organic sedimentary rock , and yes, rocks are supposed to be made of minerals and minerals can't be organic. All true, but… then there's coal. It looks like a rock and feels like a rock and is found in layers between other types of rocks — it sure sounds like a rock to me.
And so what if it breaks one little rule? Some rules are more important than others like standing quietly in the lunch line vs. Output is the same text file with the converted values and the KY county and KY , quadrangle where a coordinate is located. Originally, the network provided a group of geologists who served as resource persons for teachers.
Read more. Because coal undergoes physical and chemical changes as a result of increased heat, there is sometimes a misconception that coal is a metamorphic rock.
Coal is a sedimentary rock. Coal is altered through biological and burial-thermal processes into different ranks. Many sedimentary rocks are also altered through burial-thermal processes increasing cementation, etc.
Coal is not what most geologists would consider metamorphic rock with the possible exception of meta-anthracite, which is transitional with metamorphic rocks. Confusion arises because high-rank coals are considered the product of processes termed "low-grade burial metamorphism. Menu About Mission Statement.
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Rocks and Minerals. If you are an astute reader you are probably wondering: "How can fifty feet of plant debris accumulate in water that is only a few feet deep? It can only occur under one of two conditions: 1 a rising water level that perfectly keeps pace with the rate of plant debris accumulation; or, 2 a subsiding landscape that perfectly keeps pace with the rate of plant debris accumulation.
Most coal seams are thought to have formed under condition 2 in a delta environment. On a delta, large amounts of river sediments are being deposited on a small area of Earth's crust, and the weight of those sediments causes the subsidence. For a coal seam to form, perfect conditions of plant debris accumulation and perfect conditions of subsidence must occur on a landscape that maintains this perfect balance for a very long time. It is easy to understand why the conditions for forming coal have occurred only a small number of times throughout Earth's history.
The formation of a coal requires the coincidence of highly improbable events. Anthracite coal: Anthracite is the highest rank of coal.
It has a bright luster and breaks with a semi-conchoidal fracture. Plant debris is a fragile material compared to the mineral materials that make up other rocks. As plant debris is exposed to the heat and pressure of burial, it changes in composition and properties.
The "rank" of a coal is a measure of how much change has occurred. Sometimes the term "organic metamorphism" is used for this change. Based upon composition and properties, coals are assigned to a rank progression that corresponds to their level of organic metamorphism. The basic rank progression is summarized in the table here.
Lignite: The lowest rank of coal is "lignite. It often contains recognizable plant structures. Electricity production is the primary use of coal in the United States.
Most of the coal mined in the United States is transported to a power plant, crushed to a very small particle size, and burned. Heat from the burning coal is used to produce steam, which turns a generator to produce electricity.
Most of the electricity consumed in the United States is made by burning coal. Coal-Fired Power Plant: Photo of a power plant where coal is burned to produce electricity. The three large stacks are cooling towers where water used in the electricity generation process is cooled before reuse or release to the environment. The emission streaming from the right-most stack is water vapor.
The combustion products from burning the coal are released into the tall, thin stack on the right. Within that stack are a variety of chemical sorbents to absorb polluting gases produced during the combustion process. Coal has many other uses. It is used as a source of heat for manufacturing processes. For example, bricks and cement are produced in kilns heated by the combustion of a jet of powdered coal. Coal is also used as a power source for factories. There it is used to heat steam, and the steam is used to drive mechanical devices.
A few decades ago most coal was used for space heating. Some coal is still used that way, but other fuels and coal-produced electricity are now used instead. Coke production remains an important use of coal. Coke is produced by heating coal under controlled conditions in the absence of air. This drives off some of the volatile materials and concentrates the carbon content.
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