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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]

Coal is mostly carbon with variable amounts of other elements; chiefly hydrogen, sulfur, oxygen, and nitrogen.[2]

Coal is composed of macerals, minerals and water.[3] Fossils and amber may be found in coal.

Organic minerals[edit | edit source]

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

Abelsonites[edit | edit source]

This abelsonite is from the Green River Formation, Uintah County, Utah, US. Credit: .{{free media}}
Structure shows abelsonite.

Abelsonite has the chemical formula C

The mineral is known only from the Parachute Creek Member of the Green River Formation.[5] It has been known from the Uinta Basin in Utah since its discovery and from the Piceance Basin in Colorado since 1985.[5] Abelsonite occurs in association with albite, analcime, dolomite, mica, orthoclase, pyrite, and quartz.[4]

Abelsonite is a secondary mineral that formed in fractures, vugs, and bedding planes of oil shale.[4][5] The mineral probably formed from diagenesis of chlorophyll, likely chlorophyll a, which was transported as an aqueous solution into a favorable geologic setting.[5]

In 2003, abelsonite was fully synthesized for the first time.[6]

In 1989, abelsonite was the only known geoporphyrin to have a crystalline structure.[5][5] Most geoporphyrins occur as a series of homologues spanning a large range of carbon numbers.[5] The porphyrin which comprises abelsonite is common, but it does not usually occur in isolation from other porphyrins.[5]

The mineral is a deoxophylloerythroetioporphyrin (DPEP), with nickel occupying the center of the porphyrin ring. Most of the mineral consists of a C31 porphyrin with small quantities of a C30 norisomer.[7][4]

Evenkites[edit | edit source]

This is a coating of evenkite inside a geode. Credit: Helix84.{{free media}}

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

Fichtelites[edit | edit source]

Def. a "rare white monoclinic organic mineral, 7-isopropyl-1,4a-dimethyl-dodecahydro-1H-phenanthrene [C19H34], found in fossilized wood"[8] is called a fichtelite.

Also, occurs in "fossilized pine wood from a peat bog; in organic-rich modern marine sediment."[9]

Simonellites[edit | edit source]

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]"[10] is called a simonellite.

Kratochvilites[edit | edit source]

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"[11]

Kratochvilites have about 58.3 at % carbon.

Idrialites[edit | edit source]

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"[12] is called an idrialite.

Carpathites[edit | edit source]

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"[13] 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."[14]

Theoretical coals[edit | edit source]

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 is formed if dead plant matter decays into peat and over millions of years the heat and pressure of deep burial converts the peat into coal.[15]

Coalification starts with dead plant matter decaying into peat; then over millions of years the heat and pressure of deep burial causes the loss of water, methane and carbon dioxide and an increase in the proportion of carbon.[3] Thus first lignite (also called "brown coal"), then sub-bituminous coal, bituminous coal, and lastly anthracite (also called "hard coal" or "black coal") may be formed.[15][16]

Coal is known from Precambrian strata, which predate land plants—this coal is presumed to have originated from residues of algae.[17][18]

Coal gases[edit | edit source]

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.

Petroleums[edit | edit source]

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"[19] is called a petroleum.

Coal tars[edit | edit source]

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"[20] 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.

Naphthas[edit | edit source]

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"[21] is called a naphtha.

Malthas[edit | edit source]

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

Bitumens[edit | edit source]

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.

Pitches[edit | edit source]

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"[22] is called a pitch.

Asphalts[edit | edit source]

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"[23] is called an asphalt.

Zietrisikites[edit | edit source]

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

Ozocerites[edit | edit source]

Ozokerite is from the Bringham Young University Department of Geology, Provo, Utah, collection. Credit: Andrew Silver, USGS.

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

Ambers[edit | edit source]

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"[24] is called an amber.

Peats[edit | edit source]

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"[25] is called peat.

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

Lignites[edit | edit source]

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"[26] is called a lignite.

Jets[edit | edit source]

This is a piece of jet. Credit: Ewa Jastrzębska.

Def. a "hard, black form of coal"[27], specifically lignite is called a jet.

Bituminous coals[edit | edit source]

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

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

Anthracites[edit | edit source]

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"[28] is called anthracite.

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

Cokes[edit | edit source]

Def. a solid "residue from roasting coal"[29] is called a coke.

Fossils[edit | edit source]

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 | edit source]

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 | edit source]

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"[30] is called a coal ball.

Coal seams[edit | edit source]

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"[31] 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.

Tertiary[edit | edit source]

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

Lower Tertiary[edit | edit source]

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.

Cretaceous[edit | edit source]

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."[32]

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 | edit source]

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

Vast deposits of coal originates in former wetlands—called coal forests—that covered much of the Earth's tropical land areas during the late Carboniferous (Pennsylvanian) and Permian times.[33][34]

Coalfields[edit | edit source]

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

Peatlands[edit | edit source]

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

Hypotheses[edit | edit source]

  1. There is at least one coal seam in each geologic period.

See also[edit | edit source]

References[edit | edit source]

  1. 1.0 1.1 "coal". San Francisco, California: Wikimedia Foundation, Inc. 1 January 2015. Retrieved 2015-01-05.
  2. Blander, M. "Calculations of the Influence of Additives on Coal Combustion Deposits" (PDF). Argonne National Laboratory. p. 315. Archived from the original (PDF) on 28 May 2010. Retrieved 17 December 2011.
  3. 3.0 3.1 "Coal". British Geological Survey. March 2010.
  4. 4.0 4.1 4.2 4.3 Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W. et al., eds. Abelsonite. Chantilly, VA: Mineralogical Society of America. 
  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 Mason, G. M.; Trudell, L. G.; Branthaver, J. F. (1989). "Review of the stratigraphic distribution and diagenetic history of abelsonite". Organic Geochemistry. 14 (6): 585–594. doi:10.1016/0146-6380(89)90038-7.
  6. Zhang, B.; Lash, T. D. (September 2003). "Total synthesis of the porphyrin mineral abelsonite and related petroporphyrins with five-membered exocyclic rings". Tetrahedron Letters. 44 (39): 7253–7256. doi:10.1016/j.tetlet.2003.08.007.
  7. Storm, C. B.; Krane, J.; Skjetne, T.; Telnaes, N.; Branthaver, J. F.; Baker, E. W. (1984). "The structure of abelsonite". Science. 223 (4640): 1075–1076. doi:10.1126/science.223.4640.1075. JSTOR 1693019. PMID 17830155. S2CID 19850858. The mineral crystallizes in the triclinic crystal system.
  8. "fichtelite, In: Wiktionary". San Francisco, California: Wikimedia Foundation, Inc. 29 May 2014. Retrieved 2015-01-09.
  9. R. Ruff (2005). "Fichtelite" (PDF). Mineral Data Publishing. Retrieved 2015-01-09.
  10. "simonellite". San Francisco, California: Wikimedia Foundation, Inc. 19 June 2013. Retrieved 2015-01-09.
  11. "kratochvilite". San Francisco, California: Wikimedia Foundation, Inc. 19 June 2013. Retrieved 2015-01-09.
  12. "idrialite". San Francisco, California: Wikimedia Foundation, Inc. 20 June 2013. Retrieved 2015-01-09.
  13. "carpathite". San Francisco, California: Wikimedia Foundation, Inc. 18 June 2013. Retrieved 2015-01-09.
  14. Rob Lavinsky (20 October 2009). "Carpathite". Retrieved 2015-01-09.
  15. 15.0 15.1 "Coal Explained". Energy Explained. US Energy Information Administration. 21 April 2017. Archived from the original on 8 December 2017. Retrieved 13 November 2017.
  16. Taylor, Thomas N; Taylor, Edith L; Krings, Michael (2009). Paleobotany: The biology and evolution of fossil plants. ISBN 978-0-12-373972-8. Archived from the original on 16 May 2016. 
  17. Tyler, S.A.; Barghoorn, E.S.; Barrett, L.P. (1957). "Anthracitic Coal from Precambrian Upper Huronian Black Shale of the Iron River District, Northern Michigan". Geological Society of America Bulletin 68 (10): 1293. doi:10.1130/0016-7606(1957)68[1293:ACFPUH]2.0.CO;2. ISSN 0016-7606. 
  18. Mancuso, J.J.; Seavoy, R.E. (1981). "Precambrian coal or anthraxolite; a source for graphite in high-grade schists and gneisses". Economic Geology 76 (4): 951–54. doi:10.2113/gsecongeo.76.4.951. 
  19. "petroleum". San Francisco, California: Wikimedia Foundation, Inc. 16 July 2014. Retrieved 2015-01-09.
  20. "tar". San Francisco, California: Wikimedia Foundation, Inc. 5 January 2015. Retrieved 2015-01-09.
  21. "naphtha". San Francisco, California: Wikimedia Foundation, Inc. 16 December 2014. Retrieved 2015-01-09.
  22. "pitch". San Francisco, California: Wikimedia Foundation, Inc. 12 December 2014. Retrieved 2015-01-10.
  23. "asphalt". San Francisco, California: Wikimedia Foundation, Inc. 20 October 2014. Retrieved 2015-01-09.
  24. "amber". San Francisco, California: Wikimedia Foundation, Inc. 19 December 2014. Retrieved 2015-01-09.
  25. "peat". San Francisco, California: Wikimedia Foundation, Inc. 9 January 2015. Retrieved 2015-01-09.
  26. "lignite". San Francisco, California: Wikimedia Foundation, Inc. 16 December 2014. Retrieved 2015-01-09.
  27. "jet". San Francisco, California: Wikimedia Foundation, Inc. 15 November 2014. Retrieved 2015-01-10.
  28. "anthracite". San Francisco, California: Wikimedia Foundation, Inc. 30 January 2015. Retrieved 2015-02-09.
  29. "coke". San Francisco, California: Wikimedia Foundation, Inc. 15 December 2014. Retrieved 2015-01-09.
  30. "coal ball". San Francisco, California: Wikimedia Foundation, Inc. 10 November 2012. Retrieved 2015-01-09.
  31. "coal seam". San Francisco, California: Wikimedia Foundation, Inc. 8 October 2013. Retrieved 2015-01-09.
  32. Gaidheal1 (May 16, 2012). "Cretaceous Period". Retrieved 2012-07-24. {{cite web}}: |author= has generic name (help)
  33. Cleal, C. J. & Thomas, B. A. (2005). "Palaeozoic tropical rainforests and their effect on global climates: is the past the key to the present?" Geobiology, 3, p. 13-31.
  34. Sahney, S., Benton, M.J. & Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica" (PDF). Geology 38 (12): 1079–1082. doi:10.1130/G31182.1. 

External links[edit | edit source]