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This is an example of a hard coal or anthracite. Credit: USGS.

Coals are usually thought of as black or dark brown rocks consisting mainly of carbonized plant matter.

Types of coal include: "bituminous, anthracite, or lignite, and grades and varieties thereof."[1]

Organic minerals[edit]

An organic mineral appears to be a naturally occurring mineral containing one or more organic chemicals at a concentration of greater than 25 molecular %.


This is a coating of evenkite inside a geode. Credit: Helix84.

Def. a rare hydrocarbon mineral (CH3)2(CH2)22 or C24H50 is called an evenkite.


Def. a "rare white monoclinic organic mineral, 7-isopropyl-1,4a-dimethyl-dodecahydro-1H-phenanthrene [C19H34], found in fossilized wood"[2] is called a fichtelite.

Also, occurs in "fossilized pine wood from a peat bog; in organic-rich modern marine sediment."[3]


This is a colorless to white Simonellite on fossil wood. Credit: Thomas Witzke / Abraxas-Verlag.

Def. an "orthorhombic-dipyramidal white mineral containing carbon and hydrogen [C19H24]"[4] is called a simonellite.


Def. a "rare organic mineral [C14H10 or (C6H4)2CH2, a polymorph of fluorene], an orthorhombic hydrocarbon formed by combustion of coal or pyritic black shale deposits"[5]

Kratochvilites have about 58.3 at % carbon.


Idrialite is a very rare mineral of organic origin. Credit: Carlton Davis Collection.

Def. a "soft, orthorhombic hydrocarbon [C22H14] mineral, usually greenish-yellow to light brown in colour with bluish fluorescence"[6] is called an idrialite.


The yellow fibrous crystals are carpathite. Credit: Rob Lavinsky.

Def. a solid, homogeneous, monoclinic (space group P2/c, no. 13, or P21/c, no. 14), naturally occurring, chemical compound with the formula C24H12 that results from natural inorganic processes is called a carpathite.

Def. a "rare hydrocarbon mineral composed of coronene"[7] is called a carpathite.

"Carpathite (aka Karpatite) is a very rare organic species, being a polycyclic aromatic hydrocarbon (PAH). This striking specimen from the old Picacho Mercury Mine of California features a very interesting radial spray of highly lustrous, canary-yellow carpathite lathes to 2.0 cm on starkly contrasting, sparkly, drusy quartz."[8]

Theoretical coals[edit]

This chart shows the BGR-Classification of Coal. Credit: Bundesanstalt für Geowissenschaften und Rohstoffe (Federal Institute for Geosciences and Natural Resources).

Def. a "black rock formed from prehistoric plant remains, composed largely of carbon and burned as a fuel"[1] is called a coal.

Def. the process by which plant remains become coal is called coalification.

The chart on the right is an idealized classification of coals from peat through anthracite using total water content (%), energy content (kJ/Kg), volatiles, and surface reflectivity.

Coal gases[edit]

Main sources: Gases/Coals and Coal gases

Def. a mixture of gases (chiefly hydrogen, methane, and carbon monoxide) obtained by the destructive distillation of coal, or gas given off when coal is burned, is called coal gas.


Main sources: Liquids/Petroleums and Petroleums
This is a natural oil (petroleum) seep near Korňa, Kysucké Beskydy, Western Carpathians, Slovakia. Credit: Branork.

Def. a "flammable liquid ranging in color from clear to very dark brown and black, consisting mainly of hydrocarbons, occurring naturally in deposits under the Earth's surface"[9] is called a petroleum.

Coal tars[edit]

Main sources: Liquids/Tars/Coals and Coal tars
The lake tar pit at the La Brea Tar Pits is in Los Angeles, CA, USA. Credit: Buchanan-Hermit.

Def. a "black, oily, sticky, viscous substance, consisting mainly of hydrocarbons derived from organic materials such as wood, peat, or coal"[10] is called a tar.

Def. a thick black liquid produced by the destructive distillation of bituminous coal is called a coal tar.

It contains at least benzene, naphthalene, phenols, and aniline.


Main sources: Liquids/Naphthas and Naphthas
The beaker contains open-specification naphtha from Bangladesh. Credit:

Def. any "of a wide variety of aliphatic or aromatic liquid hydrocarbon mixtures distilled from petroleum or coal tar"[11] is called a naphtha.


Main sources: Liquids/Malthas and Malthas

Def. a black viscid substance intermediate between petroleum and asphalt is called a maltha, or malthite.


Main sources: Liquids/Bitumens and Bitumens
Here, Lussatite, an opal, occurs with bitumen. Credit: Parent Géry.

Def. a black viscous mixture of hydrocarbons obtained naturally is called a bitumen.

In the image on the right, bitumen occurs with lussatite, an opal.


Main sources: Liquids/Pitches and Pitches
Pitch Lake (Asphalt Lake) near La Brea on the island of Trinidad in the West Indies is the largest natural Tar or Bitumen Lake in the world. Credit: Richard Seaman.
Mother-of-the-Lake, Pitch Lake, is in Trinidad. Credit: Jw2c.

Def. a "dark, extremely viscous material remaining in still after distilling crude oil and tar"[12] is called a pitch.


Main sources: Liquids/Asphalts and Asphalts
Hand sample including natural asphalt, from Slovakia. Credit: Piotr Gut.

Def. a "sticky, black and highly viscous liquid or semi-solid, composed almost entirely of bitumen, that is present in most crude petroleums and in some natural deposits"[13] is called an asphalt.


Def. a natural, waxy hydrocarbon mineraloid is called a zietrisikite.


Main sources: Liquids/Ozocerites and Ozocerites
Ozokerite is from the Bringham Young University Department of Geology, Provo, Utah, collection. Credit: Andrew Silver, USGS.

Def. a natural dark, or black, odoriferous mineraloid wax is called ozokerite, or ozocerite.


Main sources: Liquids/Ambers and Ambers
These are naturally occurring amber stones. Credit: Lanzi.
This is natural blue dominican amber. Credit: Vassil.

Def. a "hard, generally yellow to brown translucent fossil resin"[14] is called an amber.


Main sources: Rocks/Coals/Peats and Peats
This is a natural reserve of peat at Frasne, France. Credit: Jeffdelonge.

Def. soil "formed of dead but not fully decayed plants found in bog areas"[15] is called peat.

Def. a brown, soil-like material characteristic of boggy, acid ground, consisting of partly decomposed vegetable matter, is called a peat.


Main sources: Rocks/Coals/Lignites and Lignites
This is a sample of lignite. Credit: Saupreiß.
Lignite seams are interlayered with calcareous mud strata. Credit: Nadirrias.

Def. a "low-grade, brownish-black coal"[16] is called a lignite.


Main sources: Rocks/Coals/Jets and Jets
This is a piece of jet. Credit: Ewa Jastrzębska.

Def. a "hard, black form of coal"[17], specifically lignite is called a jet.

Bituminous coals[edit]

A piece of bituminous coal is displayed. Credit: Amcyrus2012.

Def. a black coal having a relatively high volatile content is called a bituminous coal.


Lump of anthracite was extracted from the Ibbenbüren underground coal mine, located in Ibbenbüren, Germany. Credit: Educerva.

Def. a "form of carbonized ancient plants; the hardest and cleanest-burning of all the coals; hard coal"[18] is called anthracite.

Def. a coal of a hard variety that contains relatively pure carbon is called an anthracite.


Def. a solid "residue from roasting coal"[19] is called a coke.


Main sources: Sediments/Fossils and Fossils
Neuropteris is a common fossil in bituminous coal. Credit: Jstuby.
Lepidodendron leaf fossils are in or on a piece of bituminous coal. Credit: Martin.

Neuropteris, a fern, leaf impressions and fossils occur in bituminous coal such as in the image on the right. These coal seams and strata are dated to the Carboniferous period.

The Lepidodendrales, quillwort-like large tree-like plants from the Carboniferous also left fossils in bituminous coal as on the left.

Rocky objects[edit]

This image is of asteroid 2012 LZ1 by the Arecibo Observatory in Puerto Rico using the Arecibo Planetary Radar. Credit: Arecibo Observatory.

A rocky object is any object, including astronomical objects, composed of one or more types of rocks.

Coal balls[edit]

This is a 42-pound coal ball. Credit: RLKorotev.
This is a coal ball from southern Illinois, USA. Credit: Geni.

Def. a "nodule of plant material permeated with minerals found mostly in bituminous and anthracite coal seams"[20] is called a coal ball.

Coal seams[edit]

The coal stratigraphy of the Powder River Basin is dated. Credit: USGS.
Coal seams occur in the strata of Roome Bay. Credit: Nathan Siemers.

Def. a "stratum of coal between strata of other rocks"[21] is called a coal seam.

Both the Paleocene and Eocene of the Tertiary have coal seams in their stratigraphy, shown in the image on the right, of the Powder River Basin.

On the left is an image of coal seams in the strata of Roome Bay, Scotland.


Main sources: History/Tertiary and Tertiary

The Tertiary Period extends from 65.5 ± 0.3 to 2.588 ± 0.005 x 106 b2k.

Lower Tertiary[edit]

The coal seam occurs in the lower Tertiary. Credit: R. E. Davis, USGS.

The Yellowstone Basin in the lower Tertiary has coal seams such as the one imaged on the right, about 8 m thick.


Main sources: History/Cretaceous and Cretaceous
This stratigraphic column shows coal seams in the Pine Ridge section of the Late Cretaceous. Credit: Warren Resources.
This anthracite coal seam is in between Cretaceous sandstone layers, in Central Utah, USA. Credit: Marli Miller.

"The Cretaceous period is the third and final period in the Mesozoic Era. It began 145.5 million years ago after the Jurassic Period and ended 65.5 million years ago, before the Paleogene Period of the Cenozoic Era."[22]

The Pine Ridge section of the Late Cretaceous on the right contains coal seams.

The second image on the right exhibits an anthracite coal seam between Cretaceous sandstone strata from Central Utah, USA.

Coal measures[edit]

Def. a series of strata of the Carboniferous period, including coal seams, is called coal measures.


Def. an extensive area containing a number of underground coal deposits is called a coalfield.


Def. land consisting largely of beat or peat bogs is called a peatland.


Main source: Hypotheses
  1. There is at least one coal seam in each geologic period.

See also[edit]


  1. 1.0 1.1 "coal, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 1 January 2015. Retrieved 2015-01-05. 
  2. "fichtelite, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 29 May 2014. Retrieved 2015-01-09. 
  3. R. Ruff (2005). "Fichtelite" (PDF). Mineral Data Publishing. Retrieved 2015-01-09. 
  4. "simonellite, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 19 June 2013. Retrieved 2015-01-09. 
  5. "kratochvilite, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 19 June 2013. Retrieved 2015-01-09. 
  6. "idrialite, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 20 June 2013. Retrieved 2015-01-09. 
  7. "carpathite, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 18 June 2013. Retrieved 2015-01-09. 
  8. Rob Lavinsky (20 October 2009). "Carpathite". Retrieved 2015-01-09. 
  9. "petroleum, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 16 July 2014. Retrieved 2015-01-09. 
  10. "tar, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 5 January 2015. Retrieved 2015-01-09. 
  11. "naphtha, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 16 December 2014. Retrieved 2015-01-09. 
  12. "pitch, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 12 December 2014. Retrieved 2015-01-10. 
  13. "asphalt, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 20 October 2014. Retrieved 2015-01-09. 
  14. "amber, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 19 December 2014. Retrieved 2015-01-09. 
  15. peat. San Francisco, California: Wikimedia Foundation, Inc. 9 January 2015. Retrieved 2015-01-09. 
  16. "lignite, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 16 December 2014. Retrieved 2015-01-09. 
  17. "jet, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 15 November 2014. Retrieved 2015-01-10. 
  18. "anthracite, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 30 January 2015. Retrieved 2015-02-09. 
  19. "coke, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 15 December 2014. Retrieved 2015-01-09. 
  20. "coal ball, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 10 November 2012. Retrieved 2015-01-09. 
  21. "coal seam, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 8 October 2013. Retrieved 2015-01-09. 
  22. Gaidheal1 (May 16, 2012). "Cretaceous Period, In: Wikiversity". Retrieved 2012-07-24. 

External links[edit]

{{Geology resources}}