Coal ball facts for kids
A coal ball
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| Composition | |
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| Permineralised plant remains |
A coal ball is a type of concretion, varying in shape from an imperfect sphere to a flat-lying, irregular slab. Coal balls were formed in Carboniferous Period swamps and mires, when peat was prevented from being turned into coal by the high amount of calcite surrounding the peat; the calcite caused it to be turned into stone instead. As such, despite not actually being made of coal, the coal ball owes its name to its similar origins as well as its similar shape with actual coal.
Coal balls often preserve a remarkable record of the microscopic tissue structure of Carboniferous swamp and mire plants, which would otherwise have been completely destroyed. Their unique preservation of Carboniferous plants makes them valuable to scientists, who cut and peel the coal balls to research the geological past.
Coal balls may be found in coal seams across North America and Eurasia. North American coal balls are more widespread, both stratigraphically and geologically, than those in Europe. The oldest known coal balls date from the Namurian stage of the Carboniferous; they were found in Germany and on the territory of former Czechoslovakia.
In coal seams, coal balls are completely surrounded by coal. They are often found randomly scattered throughout the seam in isolated groups, usually in the upper half of the seam. Their occurrence in coal seams can be either extremely sporadic or regular; many coal seams have been found to contain no coal balls, while others have been found to contain so many coal balls that miners avoid the area entirely.
In 1855, two English scientists, Joseph Dalton Hooker and Edward William Binney, made the first scientific description of coal balls in England, and the initial research on coal balls was carried out in Europe. North American coal balls were discovered and identified in 1922. Coal balls have since been found in other countries, leading to the discovery of hundreds of species and genera.
Marie Stopes and D.M.S. Watson also examined coal ball samples. They agreed that coal balls formed in situ. They also added that interaction with a marine environment was necessary for a coal ball to form. In 1962, Sergius Mamay and Ellis Yochelson found signs of marine animal remains in North American coal balls.
The quality of the preservation of organic material depends on the speed of the burial process and the degree of compression before undergoing permineralisation. Generally, coal balls resulting from remains that have a quick burial with little decay and pressure have a higher preservation degree. However, plant remains in most coal balls show various signs of decay and collapse.
Related pages
Images for kids
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Calcite (middle) and dolomite (top and bottom) are common materials found in coal balls.
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A coal ball from southern Illinois
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A thin section of a plant stem depicting calcite crystals.
See also
In Spanish: Bola de carbón para niños
