Coal continued subbituminous

FIGURE 7.26 (Continued) Complex index of refracton of coal/char particles [237] (c) bituminous (BMV) (d) bituminous (BHVA) (e) subbituminous (/) lignite. 

The types of coal, in increasing order of alteration, are lignite (brown coal), subbituminous, bituminous, and anthracite. It is believed that coal starts off as a material that is closely akin to peat, which is metamorphosed (due to thermal and pressure effects) to lignite. With the further passing of time, lignite increases in maturity to subbituminous coal. As this process of burial and alteration continues, more chemical and physical changes occur and the coal is classified as bituminous. At this point, the coal is dark and hard. Anthracite is the last of the classifications, and this terminology is used when the coal has reached ultimate maturation. 

FIGURE 12.3 (continued) Aerial oxidation of subbituminous coal at various temperatures. (From Jensen, E.J. et al.. Advances in Chemistry Series No. 55, American Chemical Society, Washington, DC, 1966, p. 621.)... 

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