Maceral classes

Each of the materials recognized as belonging to a specific maceral class (according to the criteria shown in Figure 2) has physical and chemical properties that depend upon its composition in the peat swamp and the effects of subsequent metamorphic alteration. Thus, for instance, in all coals there is material derived from the structural tissues ( wood ) of plants. These woody substances (lignin, cellulose) are the dominant components of plants, and hence their derivatives dominate in typical coals. In the peat swamp some of the woody tissues may have been pyrolyzed by fire, forming a carbon-rich char recognized as fusinite in the coal. In some coal layers fusinite may be the dominant maceral, and such layers would be referred to as fusinite-rich types of coal. 

Pieces of coal are mixtures of materials somewhat randomly distributed in differing amounts. The mineral matter can be readily distinguished from the organic, which is itself a mixture. Coal properties reflect the individual constituents and the relative proportions. By analogy to geologic formations, the macerals are the constituents that correspond to minerals that make up individual rocks. For coals, macerals, which tend to be consistent in their properties, represent particular classes of plant parts that have been transformed into coal (40). Most detailed chemical and physical studies of coal have been made on macerals or samples rich in a particular maceral, because maceral separation is time consuming. 

These four classes of source materials have given rise to at least 13 coalified products that appear to be optically distinguishable. These 13 products may represent as many as nine separate sequences in which plant substances are altered to coal substances and in which the coal substances are further metamorphosed from one maceral to another. 

Figure 1. Photomicrograph of a polished surface of a bituminous coal. Representatives of the three major classes of maceral materials are identified (V), vitrinite (L), liptinite (I), inertinite.

Figure 2. Principal features of the major classes of macerals...

The methods for isolation of steroid saponins are similar to those of triterpenoid saponins. Since glycosides, as a class, are particularly prone to enzymatic or microbial degradation, processing of plant material needs to be started soon after collection to avoid delays. Air-dried powdered plant material is defatted and then extracted, either with cold or hot methanol or ethanol or with 50% aqueous ethanol or methanol at ambient temperature. Usually the extract is concentrated at reduced pressure, macerated with water, and partitioned successively using ethyl acetate and re-BuOH. Most of the saponin constituents are found in the n-BuOH soluble fraction. However, highly polar glycosides may be found in the aqueous layer. 

Fusain consists of opaque to translucent irregularly shaped masses. On the other hand, the microscopical examination of polished coal carried out under reflected light, a methodology first initiated in France, led to four different classes also called lithotypes (macerals) vitrain, clarain, durain, and fusain. Each group is characterized by a particular reflectivity and aspect. The major maceral groups are vitrinite, exinite and inertinite. 

---