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Thadguidry (talk | contribs) m Added reference for Gilbert Cady |
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|image_caption=A coal ball
|composition=Permineralised plant remains
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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|Carboniferous Period]] swamps and mires, when [[peat]] was prevented from being [[wikt:coalification|turned into coal]] by the high amount of [[calcite]] surrounding the peat; the calcite caused it to be [[permineralisation|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.
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The first [[Academic publishing|scientific description]] of coal balls was made in 1855 by Sir [[Joseph Dalton Hooker]] and [[Edward William Binney]], who reported on examples in the coal seams of [[Yorkshire]] and [[Lancashire]], England. European scientists did much of the early research.{{sfn|Scott|Rex|1985|p=124}}{{sfn|Noé|1923a|p=385}}
Coal balls in North America were first found in [[Iowa]] coal seams in 1894,{{sfn|Darrah|Lyons|1995|p=176}}{{sfn|Andrews|1946|p=334}} although the connection to European coal balls was not made until [[Adolf Carl Noé]] (whose coal ball was found by Gilbert Cady{{sfn|Darrah|Lyons|1995|p=176}}{{sfn|Leighton|Peppers|2011}}<ref>{{cite web |title=Memorial to Gilbert Haven Cady |url=https://rock.geosociety.org/net/documents/gsa/memorials/v03/Cady-GH.pdf |website=Geological Society of America |publisher=Geological Society of America |access-date=23 April 2024}}</ref>) drew the parallel in 1922.{{sfn|Noé|1923a|p=385}} Noé's work renewed interest in coal balls, and by the 1930s had drawn paleobotanists from Europe to the [[Illinois Basin]] in search of them.{{sfn|Phillips|Pfefferkorn|Peppers|1973|p=24}}
There are two theories – the autochthonous (''[[in situ]]'') theory and the allochthonous (drift) theory – that attempt to explain the formation of coal balls, although the subject is mostly speculation.{{sfn|Phillips|Avcin|Berggren|1976|p=17}}
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