Coal ball: Difference between revisions

<!--

This article is written in British English because coal balls were discovered in England, and the term "coal ball" itself is the English name for it.

Also, if you're adding a new reference, please put it in the bibliography and use {{sfn}} for the inline citation.

-->

{{Infobox rock

|name=Coal ball

}}

 

 

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.

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}}

 

 

There are two theories&nbsp;– the autochthonous (''[[in situ]]'') theory and the allochthonous (drift) theory&nbsp;– that attempt to explain the formation of coal balls, although the subject is mostly speculation.{{sfn|Phillips|Avcin|Berggren|1976|p=17}}

[[Marie Carmichael Stopes|Marie Stopes]] and [[David Meredith Seares Watson|David Watson]] analysed coal ball samples and decided that coal balls formed ''in situ''. They stressed the importance of interaction with seawater, believing that it was necessary for the formation of coal balls.{{sfn|Stopes|Watson|1909|p=212}} Some supporters of the ''in situ'' theory believe that Stopes' and Watson's discovery of a [[plant stem]] extending through multiple coal balls shows that coal balls formed ''in situ'', stating that the drift theory fails to explain Stopes' and Watson's observation. They also cite fragile pieces of organic material projecting outside some coal balls, contending that if the drift theory was correct, the projections would have been destroyed,{{sfn|Feliciano|1924|p=233}} and some large coal balls are large enough that they could never have been able to be transported in the first place.{{sfn|Andrews|1951|p=434}}

 

 

===Contents===

 

Coal balls are not made of coal;{{sfn|Andrews|1951|p=432}}{{sfn|Andrews|1946|p=327}} they are non-flammable and useless for fuel. Coal balls are calcium-rich permineralised life forms,{{sfn|Scott|Rex|1985|p=123}} mostly containing [[calcium carbonate|calcium]] and [[magnesium carbonate|magnesium]] [[carbonate]]s, [[pyrite]], and [[quartz]].{{sfn|Lomax|1903|p=811}}{{sfn|Gabel|Dyche|1986|p=99}} Other minerals, including [[gypsum]], [[illite]], [[kaolinite]], and [[lepidocrocite]] also appear in coal balls, albeit in lesser quantities.{{sfn|Demaris|2000|p=224}} Although coal balls are usually about the size of a man's fist,{{sfn|Evening Independent|1923|p=13}} their sizes vary greatly, ranging from that of a [[walnut]] up to {{convert|3|ft|0}} in diameter.{{sfn|Feliciano|1924|p=230}} Coal balls have been found that were smaller than a [[thimble]].{{sfn|Andrews|1946|p=327}}

 

 

In 1962, Sergius Mamay and Ellis Yochelson analysed North American coal balls.{{sfn|Scott|Rex|1985|p=126}} Their discovery of marine organisms led to classification of coal balls were sorted into three types: normal (sometimes known as floral), containing only plant matter; faunal, containing animal [[fossil]]s only; and mixed, containing both plant and animal material.{{sfn|Lyons et al.|1984|p=228}} Mixed coal balls are further divided into heterogeneous, where the plant and animal material was distinctly separated; and homogeneous, lacking that separation.{{sfn|Mamay|Yochelson|1962|p=196}}

==Distribution==

[[File:Coal ball from southern illinois.JPG|thumb|A coal ball from southern Illinois]]

 

The oldest coal balls were from the early end of the [[Namurian]] stage (326 to 313 mya) and discovered in Germany and former Czechoslovakia,{{sfn|Scott|Rex|1985|p=124}} but their ages generally range from the [[Permian]] (299 to 251 mya) to the [[Upper Carboniferous]].{{sfn|Jones|Rowe|1999|p=206}} Some coal balls from the US vary in age from the later end of the [[Westphalian (stage)|Westphalian]] (roughly 313 to 304 mya) to the later [[Stephanian (stage)|Stephanian]] (roughly 304 to 299 mya). European coal balls are generally from the early end of the Westphalian Stage.{{sfn|Scott|Rex|1985|p=124}}

 

==Analytical methods==

 

[[Thin section]]ing was an early procedure used to analyse fossilised material contained in coal balls.{{sfn|Phillips|Pfefferkorn|Peppers|1973|p=26}} The process required cutting a coal ball with a [[diamond saw]], then flattening and polishing the thin section with an abrasive.{{sfn|Darrah|Lyons|1995|p=177}} It would be glued to a slide and placed under a [[petrographic microscope]] for examination.{{sfn|Baxter|1951|p=531}} Although the process could be done with a machine, the large amount of time needed and the poor quality of samples produced by thin sectioning gave way to a more convenient method.{{sfn|Scott|Rex|1985|p=125}}{{sfn|Seward|2010|p=48}}

 

{{refbegin}}

{{refend}}

 

==Further reading==

 

[[Category:Carboniferous geology]]

[[Category:Mineralogy]]