Coal ball
Encyclopedia
Coal balls, despite their name, are calcium
-rich masses of permineralised life forms, generally having a round shape. Coal balls were formed roughly , during the Carboniferous Period
. They are exceptional at preserving organic matter
, which makes them useful to scientists, who cut and peel the coal balls to research the geological
past of the Earth
.
In 1855, two English scientists, Joseph Dalton Hooker
and Edward William Binney
, discovered coal balls in England, and the initial research on coal balls was carried out in Europe. It was not until 1922 that coal balls were discovered and identified in North America
. Since then, coal balls have been discovered in other countries and several theories on their formation have been proposed.
Coal balls can be found in coal seams across North America and Eurasia
. North American coal balls are relatively widespread, both stratigraphically
and geologically, as compared to coal balls from Europe. The oldest known coal balls were found in Germany and the former Czechoslovakia
.
and Edward William Binney
in northern England in 1855, and European scientists did much of the early work on these objects. Coal balls in North America were found in coal seams in the 1890s, although the connection to European coal balls was not made until Adolph Carl Noé made the connection in 1922, whose coal ball was actually found by Gilbert Cady.
Until 1922 coal balls were merely reported as "rock masses in the coal seams". Since then hundreds of new species have been discovered in coal balls in other countries, and multiple paleobotanists
have devised theories on the formation of coal balls.
(roughly ) coal balls in Yorkshire
and Lancashire
, England, Hooker and Binney proposed a theory on how coal balls were formed, which is commonly agreed upon in scientific papers.
Hooker and Binney believed that coal balls were formed in situ
– organic matter gently accumulated near a peat bog and was permineralised, a process of fossilization in which mineral deposits form internal casts of organisms. Water with a high dissolved mineral content was buried along with the plant matter in a peat bog. As the dissolved ions crystallised, concretion
s containing plant material were formed and preserved as rounded lumps of stone. This prevented coalification and preserved the peat, which eventually became a coal ball. The process is considered permineralisation because the plant material is preserved by the surrounding minerals. The majority of coal balls are found in bituminous and anthracite coal seams, in locations where the peat was not compressed sufficiently to render the material into coal.
Besides Hooker and Binney's analysis, Marie Stopes and David Watson analysed their own coal ball samples. Like Hooker and Binney they decided that coal balls formed in situ, but added that interaction with a marine environment was necessary for a coal ball to form.
, magnesium carbonate
, iron pyrite, silica, and carbonate of lime. Their sizes have been described as ranging from "the size of a walnut" to "large, round masses up to three feet in diameter", as well as "about the size of a man's fist".
Coal balls commonly contain microdolomites, products of aragonite
, and masses of organic matter at various stages of decomposition
. Hooker and Binney analysed a sample of a coal ball, finding "a lack of coniferous wood ... and fronds of fern
s", and that the discovered plant matter "appeared to [have been arranged] just as they fell from the plants that produced them". Coal balls are a good means of analyzing distribution of vegetation across wide ranges, providing evidence, for example, that "plants of the tropical belt were the same from the Ukraine to Oklahoma."
In 1962, Sergius Mamay and Ellis Yochelson discovered signs of marine animal remains in North American coal balls.
structures. Some coal balls have been found to contain preserved root hairs, and described as "more or less perfectly well-preserved" and containing "beautifully anatomically-preserved plants ... not what used to be the plant – it is the plant", while others have been described as "[containing] almost no preserved plant remains".
The quality of preservation depends on the minerals contained in it, 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 are more well preserved, although plant remains in most coal balls show various signs of decay and collapse, even in the same coal seam. Coal balls containing quantities of iron sulphide have far lower preservation than coal balls permineralised by magnesium or calcium carbonate, which has earned them the name "chief curse of the coal ball hunter".
, including Belgium
, Holland, former Czechoslovakia
, Germany, the former Soviet Union
, and more recently, China. They were also encountered in North America, where, compared to Europe, they are relatively widespread, from the Illinois Basin
to Ohio to the Appalachian region, with ages varying from the later Stephanian
(roughly ) to the later end of the Westphalian
(roughly ). European coal balls are generally from the early end of the Westphalian Stage. The age of coal balls generally range from the Permian
Period to the Upper Carboniferous, though the oldest coal balls were of early Namurian
age and were discovered in Germany and former Czechoslovakia.
ing was the first procedure used to analyse fossilised material contained in coal balls. The procedure was created and used by Hooker and Binney, and involved cutting a coal ball with a diamond saw, flattening, polishing, and gluing the thin section to a slide, then placing it under a petrographic microscope
for examination. This process could be done with a machine, although the large amount of time needed and the inferior quality of samples produced by thin sectioning gave way to a more convenient method.
The thin section technique was superseded by the now-common liquid peel technique in 1928. In the liquid peel technique, peels are obtained by cutting the surface of a coal ball with a diamond saw, grinding the cut surface on a glass plate with carborundum to a smooth finish, and etching the cut and the surface with hydrochloric acid
. The acid dissolves the mineral matter from the coal ball, and will leave a projecting layer of plant cells. Acetone
should be applied and a piece of cellulose acetate
. This embeds the cells preserved in the coal ball into the cellulose acetate. Upon drying, the cellulose acetate can be removed from the coal ball with a razor and the obtained peel can be stained with a low-acidity stain and observed under a microscope
. Up to 50 peels can be extracted from 2 millimeters of coal ball with this method.
X-ray powder diffraction has also been used to analyse coal balls. In X-ray diffraction, X-ray
s of a predetermined wavelength are sent through a sample to examine its structure. It reveals information about the crystallographic
structure, chemical composition, and physical properties
of the examined material. The scattered intensity
of the X-ray pattern is observed and analysed, with the measurements consisting of incident and scattered angle, polarisation, and wavelength or energy.
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
-rich masses of permineralised life forms, generally having a round shape. Coal balls were formed roughly , during the Carboniferous Period
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
. They are exceptional at preserving organic matter
Organic matter
Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds...
, which makes them useful to scientists, who cut and peel the coal balls to research the geological
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
past of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
.
In 1855, two English scientists, Joseph Dalton Hooker
Joseph Dalton Hooker
Sir Joseph Dalton Hooker OM, GCSI, CB, MD, FRS was one of the greatest British botanists and explorers of the 19th century. Hooker was a founder of geographical botany, and Charles Darwin's closest friend...
and Edward William Binney
Edward William Binney
Edward William Binney FRS was an English geologist.Edward William Binney was born at Morton, in Nottinghamshire in 1812, and educated at Queen Elizabeth's Grammar School, Gainsborough. He was articled to a solicitor in Chesterfield, and in 1836 settled at Manchester...
, discovered coal balls in England, and the initial research on coal balls was carried out in Europe. It was not until 1922 that coal balls were discovered and identified in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Since then, coal balls have been discovered in other countries and several theories on their formation have been proposed.
Coal balls can be found in coal seams across North America and Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
. North American coal balls are relatively widespread, both stratigraphically
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
and geologically, as compared to coal balls from Europe. The oldest known coal balls were found in Germany and the former Czechoslovakia
Czechoslovakia
Czechoslovakia or Czecho-Slovakia was a sovereign state in Central Europe which existed from October 1918, when it declared its independence from the Austro-Hungarian Empire, until 1992...
.
Discovery
Coal balls were first reported by Sir Joseph Dalton HookerJoseph Dalton Hooker
Sir Joseph Dalton Hooker OM, GCSI, CB, MD, FRS was one of the greatest British botanists and explorers of the 19th century. Hooker was a founder of geographical botany, and Charles Darwin's closest friend...
and Edward William Binney
Edward William Binney
Edward William Binney FRS was an English geologist.Edward William Binney was born at Morton, in Nottinghamshire in 1812, and educated at Queen Elizabeth's Grammar School, Gainsborough. He was articled to a solicitor in Chesterfield, and in 1836 settled at Manchester...
in northern England in 1855, and European scientists did much of the early work on these objects. Coal balls in North America were found in coal seams in the 1890s, although the connection to European coal balls was not made until Adolph Carl Noé made the connection in 1922, whose coal ball was actually found by Gilbert Cady.
Until 1922 coal balls were merely reported as "rock masses in the coal seams". Since then hundreds of new species have been discovered in coal balls in other countries, and multiple paleobotanists
Paleobotany
Paleobotany, also spelled as palaeobotany , is the branch of paleontology or paleobiology dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments , and both the evolutionary history of plants, with a...
have devised theories on the formation of coal balls.
Formation
Upon discovering Westphalian-ageWestphalian (stage)
The Westphalian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 313 and 304 Ma . It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Westphalian is named for the region of Westphalia in western Germany where strata...
(roughly ) coal balls in Yorkshire
Yorkshire
Yorkshire is a historic county of northern England and the largest in the United Kingdom. Because of its great size in comparison to other English counties, functions have been increasingly undertaken over time by its subdivisions, which have also been subject to periodic reform...
and Lancashire
Lancashire
Lancashire is a non-metropolitan county of historic origin in the North West of England. It takes its name from the city of Lancaster, and is sometimes known as the County of Lancaster. Although Lancaster is still considered to be the county town, Lancashire County Council is based in Preston...
, England, Hooker and Binney proposed a theory on how coal balls were formed, which is commonly agreed upon in scientific papers.
Hooker and Binney believed that coal balls were formed in situ
In situ
In situ is a Latin phrase which translated literally as 'In position'. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may...
– organic matter gently accumulated near a peat bog and was permineralised, a process of fossilization in which mineral deposits form internal casts of organisms. Water with a high dissolved mineral content was buried along with the plant matter in a peat bog. As the dissolved ions crystallised, concretion
Concretion
A concretion is a volume of sedimentary rock in which a mineral cement fills the porosity . Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin con meaning 'together' and crescere meaning 'to grow'...
s containing plant material were formed and preserved as rounded lumps of stone. This prevented coalification and preserved the peat, which eventually became a coal ball. The process is considered permineralisation because the plant material is preserved by the surrounding minerals. The majority of coal balls are found in bituminous and anthracite coal seams, in locations where the peat was not compressed sufficiently to render the material into coal.
Besides Hooker and Binney's analysis, Marie Stopes and David Watson analysed their own coal ball samples. Like Hooker and Binney they decided that coal balls formed in situ, but added that interaction with a marine environment was necessary for a coal ball to form.
Contents
Notwithstanding the word "coal" in their name, coal balls are not made of coal (they are not flammable and useless for fuel), but rather calcium-rich permineralised life forms, mostly containing calcium carbonateCalcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
, magnesium carbonate
Magnesium carbonate
Magnesium carbonate, MgCO3, is a white solid that occurs in nature as a mineral. Several hydrated and basic forms of magnesium carbonate also exist as minerals...
, iron pyrite, silica, and carbonate of lime. Their sizes have been described as ranging from "the size of a walnut" to "large, round masses up to three feet in diameter", as well as "about the size of a man's fist".
Coal balls commonly contain microdolomites, products of aragonite
Aragonite
Aragonite is a carbonate mineral, one of the two common, naturally occurring, crystal forms of calcium carbonate, CaCO3...
, and masses of organic matter at various stages of decomposition
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...
. Hooker and Binney analysed a sample of a coal ball, finding "a lack of coniferous wood ... and fronds of fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s", and that the discovered plant matter "appeared to [have been arranged] just as they fell from the plants that produced them". Coal balls are a good means of analyzing distribution of vegetation across wide ranges, providing evidence, for example, that "plants of the tropical belt were the same from the Ukraine to Oklahoma."
In 1962, Sergius Mamay and Ellis Yochelson discovered signs of marine animal remains in North American coal balls.
Preservation
The quality of preservation in coal balls varies from no preservation to the point of being able to analyse the cellularCell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
structures. Some coal balls have been found to contain preserved root hairs, and described as "more or less perfectly well-preserved" and containing "beautifully anatomically-preserved plants ... not what used to be the plant – it is the plant", while others have been described as "[containing] almost no preserved plant remains".
The quality of preservation depends on the minerals contained in it, 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 are more well preserved, although plant remains in most coal balls show various signs of decay and collapse, even in the same coal seam. Coal balls containing quantities of iron sulphide have far lower preservation than coal balls permineralised by magnesium or calcium carbonate, which has earned them the name "chief curse of the coal ball hunter".
Distribution
Coal balls were first found in England, and later in other parts of EurasiaEurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
, including Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
, Holland, former Czechoslovakia
Czechoslovakia
Czechoslovakia or Czecho-Slovakia was a sovereign state in Central Europe which existed from October 1918, when it declared its independence from the Austro-Hungarian Empire, until 1992...
, Germany, the former Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
, and more recently, China. They were also encountered in North America, where, compared to Europe, they are relatively widespread, from the Illinois Basin
Illinois Basin
The Illinois Basin is a Paleozoic depositional and structural basin in the United States, centered in and underlying most of the state of Illinois, and extending into southwestern Indiana and western Kentucky...
to Ohio to the Appalachian region, with ages varying from the later Stephanian
Stephanian (stage)
The Stephanian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 304 and 299 Ma . It is a subdivision of the Carboniferous system or period and the regional Silesian series...
(roughly ) to the later end of the Westphalian
Westphalian (stage)
The Westphalian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 313 and 304 Ma . It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Westphalian is named for the region of Westphalia in western Germany where strata...
(roughly ). European coal balls are generally from the early end of the Westphalian Stage. The age of coal balls generally range from the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
Period to the Upper Carboniferous, though the oldest coal balls were of early Namurian
Namurian
The Namurian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 326 and 313 Ma . It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Namurian is named for the Belgian city and province of Namur where strata of this age...
age and were discovered in Germany and former Czechoslovakia.
Analysis
Thin sectionThin section
In optical mineralogy and petrography, a thin section is a laboratory preparation of a rock, mineral, soil, pottery, bones, or even metal sample for use with a polarizing petrographic microscope, electron microscope and electron microprobe. A thin sliver of rock is cut from the sample with a...
ing was the first procedure used to analyse fossilised material contained in coal balls. The procedure was created and used by Hooker and Binney, and involved cutting a coal ball with a diamond saw, flattening, polishing, and gluing the thin section to a slide, then placing it under a petrographic microscope
Petrographic microscope
A petrographic microscope is a type of optical microscope used in petrology and optical mineralogy to identify rocks and minerals in thin sections. The microscope is used in optical mineralogy and petrography, a branch of petrology which focuses on detailed descriptions of rocks...
for examination. This process could be done with a machine, although the large amount of time needed and the inferior quality of samples produced by thin sectioning gave way to a more convenient method.
The thin section technique was superseded by the now-common liquid peel technique in 1928. In the liquid peel technique, peels are obtained by cutting the surface of a coal ball with a diamond saw, grinding the cut surface on a glass plate with carborundum to a smooth finish, and etching the cut and the surface with hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
. The acid dissolves the mineral matter from the coal ball, and will leave a projecting layer of plant cells. Acetone
Acetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...
should be applied and a piece of cellulose acetate
Cellulose acetate
Cellulose acetate , first prepared in 1865, is the acetate ester of cellulose. Cellulose acetate is used as a film base in photography, as a component in some adhesives, and as a frame material for eyeglasses; it is also used as a synthetic fiber and in the manufacture of cigarette filters and...
. This embeds the cells preserved in the coal ball into the cellulose acetate. Upon drying, the cellulose acetate can be removed from the coal ball with a razor and the obtained peel can be stained with a low-acidity stain and observed under a microscope
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
. Up to 50 peels can be extracted from 2 millimeters of coal ball with this method.
X-ray powder diffraction has also been used to analyse coal balls. In X-ray diffraction, X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s of a predetermined wavelength are sent through a sample to examine its structure. It reveals information about the crystallographic
Crystallography
Crystallography is the experimental science of the arrangement of atoms in solids. The word "crystallography" derives from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write.Before the development of...
structure, chemical composition, and physical properties
Physical property
A physical property is any property that is measurable whose value describes a physical system's state. The changes in the physical properties of a system can be used to describe its transformations ....
of the examined material. The scattered intensity
Scattering
Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of...
of the X-ray pattern is observed and analysed, with the measurements consisting of incident and scattered angle, polarisation, and wavelength or energy.