Coal is a solid fuel created from deposits of ancient vegetation that have undergone a series of metamorphic changes resulting from pressure, heat, submersion, and other natural formative processes occurring over a long period of time. Because of the different combinations of these processes acting on the vegetation and the widely differing forms of vegetation involved, coal is a complex and nonuniform substance.

The formation of peat represents a pre-coal stage of development. After increased pressure and time, lignite begins to form. The next stage is semibituminous, followed by bituminous, and then anthracite. Each of these stages is characterized by an increase in the hardness of the coal. Anthracite is the hardest of the coals. Graphite represents a post-coal developmental stage, and cannot be used for heating purposes. Coal is often classified according to the degree of metamorphic change to which it has been subjected into the following categories:

1. Anthracite
2. Bituminous
3. Semibituminous
4. Lignite

Anthracite is a clean, hard coal that burns with little or no luminous flame or smoke. It is difficult to ignite, but burns with a uniform, low flame once the fire is started. Anthracite contains approximately 14,440 Btu’s per pound, and is used for both domestic and industrial heating purposes. It’s major disadvantage as a heating fuel is its cost. Anthracite coal is divided by size into a number of different grades. Each of these grades (e.g. egg size, buckwheat size, pea size) is suitable for a specific size fire-pot.

A great amount of smoke will result if it is improperly fired. The term “bituminous coal” actually covers a whole range of coals many of which have widely differing combustion characteristics. Some of the coals belonging to this classification are hard, whereas others are soft.

The available heat for bituminous coal ranges from a low 11,000 Btu’s per pound (Indiana bituminous) to a high of 14,100 Btu’s per pound (Pocahontas bituminous). The heat value of the latter approximates that of anthracite (about 14,400 Btu’s per pound); however, unlike anthracite coal, it is available in far greater supply, a factor that makes it a very economical solid fuel to use.

Semibituminous coal is a soft coal that ignites slowly and burns with a medium length flame. Because it provides so little smoke, it is sometimes referred to as smokeless coal.

Lignite (sometimes referred to as brown coal) ignites slowly, produces very little smoke, and contains a high degree of moisture. In structure, it is midway between peat and bituminous coal. Lignite contains approximately half the available heat of anthracite (or about 7400 Btu’s per pounds), and burns with a long flame. Its fire is almost smokeless, and it does not coke, a characteristic, which it shares with anthracite. Lignite is considered a low-grade fuel, and its calorific value is low when compared with the other coals. Moreover, it is difficult to handle and store.

Coal (?), n. [AS. col; akin to D. kool, OHG. chol, cholo, G. kohle, Icel. kol, pl., Sw. kol, Dan. kul; cf. Skr. jval to burn. Cf. Kiln, Collier.]


A thoroughly charred, and extinguished or still ignited, fragment from wood or other combustible substance; charcoal.

2. Min.

A black, or brownish black, solid, combustible substance, dug from beds or veins in the earth to be used for fuel, and consisting, like charcoal, mainly of carbon, but more compact, and often affording, when heated, a large amount of volatile matter.

⇒ This word is often used adjectively, or as the first part of self-explaining compounds; as, coal-black; coal formation; coal scuttle; coal ship. etc.

⇒ In England the plural coals is used, for the broken mineral coal burned in grates, etc.; as, to put coals on the fire. In the United States the singular in a collective sense is the customary usage; as, a hod of coal.

Age of coal plants. See Age of Acrogens, under Acrogen. -- Anthracite or Glance coal. See Anthracite. -- Bituminous coal. See under Bituminous. -- [Blind coal[. See under Blind. -- Brown coal, ∨ Lignite. See Lignite. -- Caking coal, a bituminous coal, which softens and becomes pasty or semi-viscid when heated. On increasing the heat, the volatile products are driven off, and a coherent, grayish black, cellular mass of coke is left. -- Cannel coal, a very compact bituminous coal, of fine texture and dull luster. See Cannel coal. -- Coal bed Geol., a layer or stratum of mineral coal. -- Coal breaker, a structure including machines and machinery adapted for crushing, cleansing, and assorting coal. -- Coal field Geol., a region in which deposits of coal occur. Such regions have often a basinlike structure, and are hence called coal basins. See Basin. -- Coal gas, a variety of carbureted hydrogen, procured from bituminous coal, used in lighting streets, houses, etc., and for cooking and heating. -- Coal heaver, a man employed in carrying coal, and esp. in putting it in, and discharging it from, ships. -- Coal measures. Geol. (a) Strata of coal with the attendant rocks. (b) A subdivision of the carboniferous formation, between the millstone grit below and the Permian formation above, and including nearly all the workable coal beds of the world. -- Coal oil, a general name for mineral oils; petroleum. -- Coal plant Geol., one of the remains or impressions of plants found in the strata of the coal formation. -- Coal tar. See in the Vocabulary. -- To haul over the coals, to call to account; to scold or censure. [Colloq.] -- Wood coal. See Lignite.


© Webster 1913.

Coal, v. t. [imp. & p. p. Coaled (?); p. pr. & vb. n. Coaling.]


To burn to charcoal; to char.


Charcoal of roots, coaled into great pieces.


To mark or delineate with charcoal.



To supply with coal; as, to coal a steamer.


© Webster 1913.

Coal, v. i.

To take in coal; as, the steamer coaled at Southampton.


© Webster 1913.

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