An Organic Rock

Coal and coal products will play an increasingly important role in fulfilling the energy needs of society. Future applications will extend far beyond the present major uses for power generation (Chapter 15) and chemicals production (Chapter 24). A key feature in these extensions will be the development of means to convert coal from its native form into useful gases and liquids in ways that are energy-efficient, nonpolluting, and economical. 

The design of a new generation of conversion processes will require a deeper understanding of coal s intrinsic properties and the ways in which it is chemically transformed under process conditions. Coal properties such as the chemical form of the organic material, the types and distribution of organics, the nature of the pore structure, and the mechanical properties must be determined for coals of different ranks (or degrees of coalification) in order to use each coal type most effectively. 

Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials (Chapter 3). 

Briefly, sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks (1) clastic sedimentary rocks, such as breccia, conglomerate, sandstone, and shale, which are formed from mechanical weathering debris, (2) chemical sedimentary rocks, such as rock salt and some limestone rocks, which form when dissolved materials precipitate from solution, and (3) organic sedimentary rocks, such as coal and some limestone rocks, which form from the accumulation of plant or animal debris. 

Chemical sediments are created by a precipitation of low temperature/pressure minerals from water solution onto a depositional surface or within sediment pores. Depending on the acidity, oxidation, temperature, or salinity, a variety of chanical sedimentary rock may result. Examples of chemical sediments include carbonates, evaporites, opal, chert (may form in other ways too), iron oxides, and aluminum oxides. Chanical textures are usually o-ystaUine with some special terms, such as oolitic or pisolitic. Sandstone is a clastic sedimentary rock made up mainly of sand-size (1/16 to 2 mm diameter) weathering debris. 

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Coal has been described as an organic rock. In order to better utilize coal supplies, however, the chemical structure of coal needs to be known in much greater detail so that methods can be developed to convert coal to a clean burning liquid or gaseous fuel. 

Coal is an organic rock that can be converted by heat treatment into a variety of products (Fig. 1). 

Coal is an organic rock-like natural product (Speight, 1994) whose beginnings were as the remains of flora that accumulated as peat. The accumulation occurred in submerged conditions, thereby preventing complete decay of the organic... 

Coal may be viewed as an organic rock. As such, it has an organic, an inorganic, and a physical structure. It is by nature a heterogeneous substance that varies from millimeter to millimeter in the same seam coals of different rank formed from different species of plant matter during different geological periods in swamps hundreds or thousands of miles apart vary just as much. While it may not be possible to determine a coal structure absolutely, it is possible to determine key structural features of coals that affect their reactivity and ultimately their utility. 

Coal is defined as an organic rock composed of carbon, hydrogen, oxygen, nitrogen, sulfur, and mineral matter. Its conversion to useful products is typically carried out by reacting air, oxygen, steam, carbon dioxide, hydrogen, or a... 

Chapter 4). It is unnecessary to repeat this discussion except to note that this particular aspect of coal science (petrography) deals with the individual components of coal as an organic rock (Chapter 4) whereas the nomenclature, terminology, and classification systems are intended for application to the whole coal. Other general terms that are often applied to coal include rank and grade, which are two terms that describe the particular characteristics of coal. 

In the chemical and geological senses, coal is an organic natural product or, more correctly, an organic rock formed from partially decomposed (and decomposing) plant debris (and, in some cases, animal debris) which had collected in regions where waterlogged swampy conditions prevailed (Terres, 1931 Lowry, 1945 Francis, 1961 Lowry, 1963 Murchison and Westoll, 1968 Elliott, 1981 Bend et al., 1991 Bend, 1992). These conditions prevented complete decay of the debris (to carbon dioxide and water) as it accumulated and was subsequently metamorphosed to eventually lead to the material now known as coal. 

Peat is considered (by some investigators) to be low-rank coal it is not sufficiently natural to be classed as an organic rock but it is no longer merely a collection of organic debris. 

The nomenclature employed to define coal as an organic rock distinguishes between the rock types (lithotypes) and their microscopic constituents. These constituents are called macerals by analogy with the minerals which occur in inorganic rocks. Identification of the macerals requires that the... 

Coal An organic rock a stratified combustible carbonaceous rock, formed by partial to complete decomposition of vegetation varies in color from dark brown to black not fusible without decomposition and very insoluble. 

Coal is an organic rock, being grossly characterized by layers or bands having glossy or dull appearances. The glossy layers are composed mainly of vitrinite, formed from... 

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