Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.

History:

Early coal extraction was small-scale, the coal lying either on the surface, or very close to it. Typical methods for extraction included drift mining and bell pits. As well as drift mines, small scale shaft mining was used. This took the form of a bell pit, the extraction working outward from a central shaft, or a technique called room and pillar in which 'rooms' of coal were extracted with pillars left to support the roofs. Both of these techniques however left considerable amount of usable coal behind.

Archeological evidence in China indicates surface mining of coal and household usage after approximately 3490 BC.

The earliest reference to the use of coal in metalworking is found in the geological treatise On stones by the Greek scientist Theophrastus (c. 371–287 BC).

 

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