Modern coal petrology requires rapid and precise description of great numbers of coal core or bench samples in order to acquire the information required to understand and predict vertical and lateral variation of coal quality for correlation with coal-bed thickness, depositional environment, suitability for technological uses, etc. Procedures for coal description vary in accordance with the objectives of the description. To achieve our aim of acquiring the maximum amount of quantitative information within the shortest period of time, we have adopted a combined megascopic-microscopic procedure. Megascopic analysis is used to identify the distinctive lithologies present, and microscopic analysis is required only to describe representative examples of the mixed lithologies observed. This procedure greatly decreases the number of microscopic analyses needed for adequate description of a sample. For quantitative megascopic description of coal microlithotypes, microlithotype assemblages, and lithotypes, we use (V) for vitrite or vitrain, (E) for liptite, (I) for inertite or fusain, (M) for mineral layers or lenses other than iron sulfide, (S) for iron sulfide, and (X₁), (X₂), etc. for mixed lithologies. Microscopic description is expressed in terms of V representing the vitrinite maceral group, E the exinite group, I the inertinite group, and M mineral components. volume percentages are expressed as subscripts. Thus (V)₂₀(V₈₀E₁₀I₅M₅)₈₀ indicates a lithotype or assemblage of microlithotypes consisting of 20 vol. % vitrite and 80% of a mixed lithology having a modal maceral composition V₈₀E₁₀I₅M₅. This bulk composition can alternatively be recalculated and described as V₈₄E₈I₄M₄. To generate these quantitative data rapidly and accurately, we utilize an automated image analysis system (AIAS). Plots of VEIM data on easily constructed ternary diagrams provide readily comprehended illustrations of the range of modal composition of the lithologic units making up a given coal bed. The use of bulk-specific-gravity determinations is alo recommended for identification and characterization of the distinctive lithologic units.

The availability of an AIAS also enhances the capability to acquire textural information. Ranges of size of maceral and mineral grains can be quickly and precisely determined by use of an AIAS. We assume that shape characteristics of coal particles can also be readily evaluated by automated image analysis, although this evaluation has not yet been attempted in our laboratory.

Definitive data on the particulate mineral content of coal constitute another important segment of petrographic description. Characterization of mineral content may be accomplished by optical identification, electron microprobe analysis, X-ray diffraction, and scanning and transmission electron microscopy. Individual mineral grains in place in polished blocks or polished this sections, or separated from the coal matrix by sink-float methods are studied by analytical techniques appropriate to the conditions of sampling.