GEOLOGICAL SURVEY CIRCULAR 894 

Recommended Procedures · 

and Methodology of Coal 

Description 
Recommended Procedures and Methodology 

of Coal Description 

By E. C. T. Chao, J. A. Minkin, and C. L. Thompson 

GEOLOGICAL SURVEY CIRCULAR 894 

Steps and methods to be followed to characterize, 

rapidly and quantitatively, the distinctive 

properties and profiles of a given coal bed 

1983 
United States Department of the Interior 

JAMES G. WATT, Secretary 

Geological Survey 

Dallas L. Peck, Director 

Library of Congress Cataloging in PubHcation Data 

Chao, E. C. T. 

Recommended procedures and methodology of coal description. 

(Geological Survey circular; 894) 

"This document is the result of a workshop on coal description held for the Branch of Coal Resources of the U.S. Geological Survey in 

March 1982" -Abstract. 

Bibliography: p. 

Supt. of Docs. no.: I 19.4/2:894 

1. Coal-Analysis. I. Minkin, .J. A. II. Thompson, C. L. III. Title. IV. Series. 

QE75.C5 no. 894 557.3s [553.2'4'0287] 83-600078 rrP325] 

Free on application to Distribution Branch, Text Products Section, 

U. S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 
Abstract - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Introduction-----------------------------------

Nomenclature, identification, and classification--------

Quantitative nomenclature --------------------

Categories and degree of details of megascopic and 

microscopic coal description ------------------

Types of descriptive information required for different 

purposes ---------------------------------

Coal chemistry and technologically related information ----------------------------------

Coal washability and preparation information --

Coal-bed profiles -------------------------

Information related to geologic processes------

Information for coal-bed correlation----------

Sampling and sample collecting techniques-----------

Examples of past and current methods of coal description -------------------------------------

CONTENTS 

Page 

1 

1 

2 

10 

11 

12 

12 

12 

12 

12 

12 

12 

16 

Page 

Proposed methodology and recommended procedures 

for coal and coal-bed profile description based on 

quantitative petrography -------------------- 17 

Conditions and expectations of megascopic observation, examination, and description-------- 17 

Megascopic recognition of macerals and microlithotypes ------------------------- 18 

Bridging the gap between megascopic and 

microscopic observations ------------- 18 

Procedures for first- and second-round laboratory 

megascopic description ------------------ 18 

Methods of AlAS quantitative analysis ---------- 20 

Selection of chips for further investigations------- 22 

Data presentation and use ------------------------ 24 

Quantitative coal-bed description: A new data base ----- 26 

Summary: The why, what, who, and how of coal description ------------------------------------- 27 

References cited -------------------------------- 28 

ILLUSTRATIONS 

Page 

FIGURE 1. Microlithotype ternary diagram ---------------------------------------------------------- 4 

2A -3A. Photographs showing: 

2A. Split drill core of bituminous coal from the Hazard coal, Knott County, Ky ----------------- 5 

2B. Split drill core from the Emery Coalfield, central Utah--------------------------------- 5 

3A. Enlarged view of lower outlined area shown in figure 2A ------------------------------- 6 

3B-3E. Photomicrographs showing: 

3B. Enlarged view of upper outlined area shown in figure 3A ------------------------------- 6 

3C. Enlarged view of area outlined in figure 3B ----------------------------------------- 6 

3D. Enlarged view of lower outlined area shown in figure 3A ------------------------------- 6 

3E. Enlarged view of area outlined in figure 3D ----------------------------------------- 6 

3F. Photograph showing enlarged view of upper outlined area shown in figure 2A ---------------------- 7 

3G, 3H. Photomicrographs showing enlarged views of areas outlined in: 

3G. Figure 3F ------------------------------------------------------------------- 7 

3H. Figure 3G ------------------------------------------------------------------- 7 

4A. Photograph showing block sample of bituminous coal from the No. 6 coal, Webster County, Ky --------

4B. Photomicrograph showing enlargement of area outlined in figure 4A ----------------------------- 8 

4C. Photograph showing polished area on block sample of bituminous coal from the No. 6 coal, Webster 8 

County,Ky------------------------------------------------------------------------- 9 

4D. Photomicrograph showing enlargement of microlithotype area outlined in figure 4C ___ __:_____________ 9 

5. Columnar profile for the portion of drill-core sample shown in figure 2A --------------------------- 10 

6. Petrographic profile of the Permian Garrick seam of Australia----------------------------------- 11 

7, 8. Coal-bed profiles showing: 

7. Correlation of microlithotype and miospore distribution of a Carboniferous coal from Great 

Britain -------------------------------------------------------------------- 13 

8. Use of microlithotype distribution for correlating eastern and western parts of Wilhelm coal 

bed, Germany -------------------------------------------------------------- 14 

9. Diagram showing proposed method of obtaining a columnar sample of coal bed --------------------- 15 

10. Flow diagram of the Joyce-Loebl MAGISCAN automated image analysis system------------------- 20 

Ill 
11-13. Photographs showing: 

11A. Overall configuration of the MAG I SCAN automated image analysis system ---------------

liB. Setup for macroscopic analysis of hand samples with the MAGISCAN automated image 

analysis system -------------------------------------------------------------

12A. TV screen view of a split core of I coal from Emery Coalfield, central Utah-----------------

128. Segmentation of vitrite-rich areas in the same field shown in figure 12A -------------------

13A. TV screen view of area in polished block of No.6 coal from Webster County, Ky -------------

13B. Segmentation of exinite in the same field shown in figure 13A ---------------------------

14A, 14B. Photomicrographs showing: 

14A. Area of vitrite in polished thin section of bituminous coal from Upper Freeport coal, Indiana 

County,Pa-----------------------------------------------------------------

14B. Polished thin section of commercial cannel coal from eastern Kentucky-------------------

15-16B. Ternary diagrams showing: 

15. Petrographic characteristics of Tertiary, Cretaceous, and Gondwana coals of the West Pacific 

and India ------------------------------------------------------------------

16A. Recommended ternary diagram for plotting microscopic modal compositions of mixed microlithotype lithologies to show stratigraphic variations for a single drill-core sample of a coal 

bed (Hazard coal, Knott County, Ky.) --------------------------------------------

16B. Average total VEIM compositions for thickness intervals of the coal sample shown in figure 

16A ----------------------------------------------------------------------

TABLES 

P,age 

21 

21 

22 

22 

23 

23 

24 

24 

25 

26 

27 

Page 

TABLE 1. Macerals in bituminous coals------------------------------------------------------------------- 3 

2. Macerals in brown coals and lignites -------------------------------------------------------------- 3 

APPENDICES 

Page 

APPENDIX 1. Procedure for laboratory megascopic description of coal-Block or drill-core samples--------------------- 29 

2. The in-place polish procedure----------------------------------------------------------------- 29 

3. Checklist for binocular megascopic description --------------------------------------------------- 30 

IV 
Recommended Procedures and Methodology 

of Coal Description 

By E. C. T. Chao, J. A. Minkin, and C. L. Thompson 

Abstract 

This document is the result of a workshop on coal description 

held for the Branch of Coal Resources of the U.S. Geological 

Survey in March 1982. It has been prepared to aid and encourage the field-oriented coal scientist to participate directly 

in petrographic coal-description activities. 

The objectives and past and current practices of coal description vary widely. These are briefly reviewed and illustrated with examples. Sampling approaches and techniques for 

collecting columnar samples of fresh coal are also discussed. 

The recommended procedures and methodology emphasize 

the fact that obtaining a good megascopic description of a coal 

bed is much better done in the laboratory with a binocular 

microscope and under good lighting conditions after the 

samples have been cut and quickly prepared. For better observation and cross-checking using a petrographic microscope for 

identification purposes, an in-place polishing procedure (requiring less than 2 min) is routinely used. Methods for using both 

the petrographic microscope and an automated image analysis 

system are also included for geologists who have access to such 

instruments. 

To describe the material characteristics of a coal bed in terms 

of microlithotypes or lithotypes, a new nomenclature of (V), (E), 

(1), (M). (S). (X,). (X.I. and so on is used. The microscopic 

description of the modal composition of a megascopically 

observed lithologic type is expressed in terms of (VEIM); 

subscripts are used to denote the volume percentage of 

each constituent present. 

To describe a coal-bed profile, semiquantitative data (without microscopic study) and quantitative data (with microscopic 

study) are presented in ready-to-understand form. The average 

total composition of any thickness interval or of the entire coal 

bed can be plotted on a triangular diagram having V, E, and 

I+ M +S as the apices. The modal composition of any mixed 

lithologies such as (X1), (X2), and so on can also be plotted on 

such a triangular ternary diagram. Such diagrams can be used 

either for tracing compositional variations throughout a single 

coal-bed profile or for comparing variations between different 

coal beds. 

INTRODUCTION 

This document is based on material presented at 

a workshop for the U.S. Geological Survey's 

Branch of Coal Resources on March 4, 5, and 8, 

1982. It has been prepared to serve two major 

objectives: (1) to present, particularly for the 

benefit of field-oriented coal-research scientists, 

procedures and methodology that have been developed for rapid, semiquantitative to quantitative 

characterization of bituminous coals, especially 

megascopic coal-bed profiles, and (2) to encourage 

the field-oriented coal scientist or his assistant 

to participate directly in coal-description activities without having to rely on results from coal 

petrographers. 

For both megascopic and microscopic quantitative characterization of coal, we normally recommend using an automated image analysis system 

(AlAS) and presenting the descriptive data in columnar sections and triangular diagrams using the 

VE IM nomenclature described below and discussed in detail by Chao and others (1982a, b). Not 

all field-oriented coal scientists, however, will have 

access to an AlAS or to a research petrographic 

microscope, nor will they have the time or the inclinatie:::i to describe the coal or coal bed as a coal 

petrographer would. Therefore, the emphasis of 

this document is on the procedures and methodology for preparing coal drill-core or block samples 

to obtain the maximum amount of descriptive 

petrographic data quickly by using a binocular 

microscope under laboratory lighting and space 

conditions. Methods involving the petrographic 

microscope and the AlAS are also included here 

for geologists who do have access to such 

instruments. 

Those engaged in coal investigations need to describe coal beds in their study area to make their 

maps and their reports more meaningful and complete. The description of a particular coal bed 

should bring out its characteristics, such as certain properties that are similar to or different from 

those of other coal beds, and should evaluate 

whether these features vary locally or are consistent regionally. 
Objectives of coal description will differ according to whether the work is to be done in the field or 

carried out in the laboratory. These objectives 

must fit either the purposes of the study and the 

problems to be solved (coal preparation, utilization, sale, mining operations) or the geologic 

studies for developing models of depositional and 

geochemical environments to predict coal-bed 

variations. 

The motives for developing a rapid quantitative 

descriptive methodology are rooted in the question, "Why hasn't coal petrography played a major role in coal geology, coal mining, or coal 

chemistry investigations?" The two main reasons 

probably are: 

1. Obtaining coal petrographic descriptions in the 

past was time consuming. Once the 

samples had been collected and prepared 

and the investigations had been completed, 

it took months or even years before the results were available for use by coal geologists, coal-mining engineers, or coal 

chemists. For petrographic study results to 

be of value, the study/ must be completed in 

a timely fashion. Therefore, the speed of 

obtaining petrographic data must be 

increased. 

2. After a detailed petrographic study had been 

completed, the data presented included 

many technical terms, some of which were 

ambiguous, and quantitative data painstakingly obtained were presented in 

difficult-to-follow graphic form. To make 

the results of petrographic study more convenient and immediately useful to other 

coal scientists, the use of ambiguous technical terms in petrographic descriptions 

should be reduced, and graphic display of 

the detailed quantitative data on coal composition and characteristics should be 

simplified. 

These objections and needs should be satisfied 

by the procedures recommended below. 

NOMENCLATURE, IDENTIFICATION, 

AND CLASSIFICATION 

To minimize possible confusion and to provide 

the field-oriented coal scientist with a quick reference to the terms used in describing coal com2 

ponents, some of the terms and examples of 

organic and inorganic single and aggregate components are given and are illustrated as follows: 

Megascopic (macroscopic) observation or description. The term "megascopic" is defined in the 

Glossary of Geology (Bates and Jackson, 1980) as, 

"Said of an object or phenomenon, or of its characteristics, that can be observed with the unaided 

eye or with a hand lens." In our usage, megascopic 

observation is made with the naked eye, with a 

hand lens, or with a low-magnification binocular 

microscope (generally about lOX and in no case in 

excess of 32X). 

Microscopic observation or description. The 

term "microscopic" is defined in the Glossary of 

Geology (Bates and Jackson, 1980) as, "Said of an 

object or phenomenon or of its characteristics that 

cannot be observed without the aid of a microscope.'' In our usage, the microscope is a research 

petrographic microscope with a minimum magnification of 56 X. 

Macerals. A coal description must deal with 

both organic and inorganic components. The 

organic components of coal, equivalent to mineral 

species of the mineral kingdom, are called 

macerals. They generally have a range of organic 

composition that depends on the plant materials 

from which they are derived and on the degree of 

coalification or rank of the coal. Optically, in either 

reflected or transmitted light, they generally can 

be identified by their shape, color, fluorescence 

characteristics, and reflectance or index of refraction. X-ray diffraction patterns for macerals show 

diffuse and broad peaks characteristic of amorphous or poorly crystallized substances. The major chemical components of macerals are the light 

elements H, C, N, 0, and S. Modem equipment can 

now quantitatively analyze most of these light 

elements in place except hydrogen. Because 

macerals also have a range of hydrogen-to-carbon 

ratios, a definitive maceral identification by microprobe analytical methods is still in the future. Coal 

macerals currently are identified petrographically 

on the basis of their optical and textural properties, which are sometimes not entirely free of ambiguity. All maceral names end in "nite." The 

maceral groups are vitrinite, exinite or liptinite, 

and inertinite. Table 1 lists the macerals found in 

bituminous coals (International Committee for 

Coal Petrology (ICCP), 1971, 1975). Low-rank 

coals (subbituminous and lignite) contain precursors of some of the macerals of bituminous coals. 
TABLE I.-Macerals in bituminous coals 

[Stopes-Heerlen system, after International Handbook of Coal Petrography (1963, 

1971, 1975). Macerals are described by Stach and others (1975)) 

Maceral group Maceral 

Vitrinite ----------------------------- Collinite 

Telinite 

Vitrodetrinite 

Exinite-liptinite ----------------------- Sporinite 

Cutinite 

Resinite 

Alginite 

Liptodetrinite 

Inertinite ---------------------------- Micrinite 

Macrinite 

Semifusinite 

Fusinite 

Sclerotinite 

Inertodetrinite 

TABLE 2.-Macerals in brown coals and lignites 

[After International Handbook of Coal Petrography (1963, 1971, 1975). Macerals 

are described by Stach and others (1975)) 

Maceral group Maceral 

Huminite --------------------------- Textinite 

Ulminite 

Attrinite 

Densinite 

Gelinite 

Corpohuminite 

Liptinite ---------------------------- Sporinite 

Cutinite 

Resinite 

Alginite 

Liptodetrinite 

Chlorophyllinite 

Suberinite 

Bituminite 

Inertinite --------------------------- Sclerotinite 

Inertodetrinite 

Fusinite 

Semifusinite 

Macrinite 

3 

Some maceral names for these coals are different 

(table 2) but will not be discussed here. 

Microlithotype. The term "microlithotype" is 

defined in the International Handbook of Coal 

Petrography (International Committee for Coal 

Petrology, 1971) as ''a typical association of 

macerals in coals, occurring in bands at least 50 

microns wide. Microlithotype names bear the suffix 'ite.' , 

Basically, microlithotypes can be subdivided 

into monomacerite (consisting of macerals of a 

single maceral group), bimacerite (macerals of two 

maceral groups), and trimacerite (macerals of all 

three maceral groups). Figure 1 is a ternary diagram that illustrates the various microlithotype 

terms approved by the International Committee 

for Coal Petrology (1971, 1975). Additional microlithotype names, such as carbominerite and carbosilicite, indicate combinations of macerals and 

minerals. As figure 1 shows, the names for trimacerites are long, and their compositions cover a 

wide range; hence, their usefulness in coal description becomes limited. As will be discussed below 

and as figure 1 shows, microlithotype compositions can be more specifically represented in terms 

of volume percentages of vitrinite, exinite, and 

inertinite. 

Assemblages of microlithotypes. The maximum 

width of a microlithotype is not defined clearly. In 

different countries, however, the minimum band 

thickness of a lithotype varies from 3 mm to 1 em 

(Cameron, 1978). We use assemblages of microlithotypes to mean an association of two or more 

microlithotypes in alternating lamellae or overlapping lenses in thicknesses up to 2 mm or more; 

then other terms become more appropriate. 

Lithotype. The International Committee for 

Coal Petrology (1963) defines "lithotype" as "a 

macroscopically visible band in humic coals, 

analyzed by physical characteristics rather than 

by botanical origin. The four lithotypes of banded 

bituminous coal are vitrain, clarain, durain and 

fusain. These were originally described by Stopes 

in 1919." The American Society for Testing and 

Materials (1980) includes in this definition attrital 

coal and any specific mixture of two or more of the 

five principal lithotypes, such as clarodurain. Most 

petrographers are aware that lithotypes contain 

microlithotypes and (or) assemblages of microlithotypes. Examples of lithotypes and microlithotypes are shown in figures 2, 3, and 4. 
Vitril)ite Group 

~Vi trite) 

<i.lroclarite 

(trimacerites) 

clarodurite 

vitrinertoliptite 

Durite E Durite Durite I 

(Liptite)._____,. _ _,._ ___ _,v'-------"----...L.------.-~r---.-.lt...---~v---~v'----~--lL--.l(Jnertite) 

ExiniteGroup Inertinite Group 

FIGURE !.-Microlithotype ternary diagram. The VEl point is much more specific than the generalized areas represented by 

ICCP-recommended microlithotype names. 

Mixed lithologies (X1), (X2), (X3), and so on. For 

megascopic description, the lithotype terms 

clarain, clarodurain, and durain are not much more 

informative than the terms bright, medium-bright, 

and dull attrital coals. Instead, for quantitative description of megascopically discernible units other 

than the pure lithotypes vitrain and fusain, we 

have adopted the term "mixed lithologies." Mixed 

lithologies are mixtures or assemblages of microlithotypes. 

4 

In analogy to brightness differences, the mixed 

lithologies (X1), (X2), (X3), and so forth are characterized by differences in light scattering and reflecting characteristics (figs. 3, 4) when they are 

viewed with the naked eye, the hand lens, and (or) 

the binocular microscope. When the sample surface is prepared consistently and uniformly 

(ground flat and partially polished with 800-grit 

abrasives), the light scattering and reflecting properties of (X3) are distinctly greater or stronger than 
25.61-

25.62-

en 25.63- a: 

w 

1--

w 

::2E 25.64-

z 

::i 

1--

Q.. 

w 

0 

25.66-

25.67-

20-

30~ 

40-

50-

60-

en 

a: 

w 

1-- 70- w 

::2E 

:::::i 

...J 80- ~ 

~ 

. 90-

J: 

1--

(!) 

~100-

...J 

110-

120-

130-

140-

150-

5 

FIGURE 2A.-Split drill core of bituminous coal, ground flat 

and polished with 800-grit abrasives, showing a welldeveloped banded or layered structure. The dark bands are 

made up of the microlithotype vitrite or the lithotype vitrain 

(depending on the width of a particular band). The light-gray 

bands are assemblages of microlithotypes or mixed lithologies. The well-banded texture is typical of coal of 

autochthonous origin. A quantitative megascopic description of this portion of the coal bed is shown in figure 5. The 

lower outlined area is enlarged and illustrated in figures 3A 

to 3E and the upper outlined area in figures 3F to 3H. 

Hazard coal, Knott Coun~, eastern Kentucky. 

FIGURE 2B.-Split drill core, ground flat and polished with 

800-grit abrasives, showing irregular lenses of vitrite and 

vitrain in juxtaposition with less vitrinite rich layers. We interpret this texture as typical of a coal of allochthonous 

origin, where the plant material was transported from the 

growth site to the site of deposition before coalification. I 

coal, Cretaceous Ferron Sandstone Member of the Mancos 

Shale, Emery Coalfield, central Utah. 
3A 

3B 

FIGURE 3A.-Enlarged view of lower outlined area shown in 

figure 2A. This area of the sample has been polished in place 

with 1- and 1/4-JLID. diamond abrasives. Shown are an assemblage of microlithotypes consisting of alternating bands and 

lenses of vitrite (dark) and mixed lithologies (light gray). The 

areas outlined are shown at higher magnifications in succeeding photomicrographs. Hazard coal, Knott County, eastem Kentucky. Photograph (shown actual size) was taken 

through a binocular microscope at 32X in diffuse illumination. 

FIGURE 3B.-Enlarged view of upper outlined area shown in 

figure 3A. A microlithotype band of a trimacerite (bracket) 

containing dark mineral grains and lenses of white inertite 

lies between smooth and featureless microlithotype bands of 

vitrite. Three lenses of fusinite-semifusinite having cell structures are seen in the upper part of the photomicrograph. The 

outlined area of mixed lithology (X1) is shown at higher 

magnification in figure 3C. Photomicrograph taken with reflected light, oil immersion. 

FIGURE 3C.-Enlarged view of area outlined in figure 3B. The 

mixed lithology (X1) is shown to consist of lenses of fusinite 

above and below a band consisting of vitrinite (gray) containing dark elongate sporinites and white inertinites. Photomicrograph taken with reflected light, oil immersion. 

3C 
FIGURE 3D.-Enlarged view of lower outlined area shown in 

figure 3A. The mixed lithology (X2) is bounded by microlithotype vitrite lenses (smooth gray area). The outlined area 

is shown at higher magnification in figure 3E. Photomicrograph taken with reflected light. 

FIGURE 3E.-Enlarged view of area outlined in figure 3D showing details of mixed lithology (X2) containing dark exinite 

(mostly sporinite) and white inertinite in a matrix of gray 

vitrite. Photomicrograph taken with reflected light, oil 

immersion. 

FIGURE 3F.-Enlarged view of upper outlined area shown in 

figure 2A. The light-colored band is dominantly mixed lithology (X3) containing abundant inertinite. The bronzy gray inertite is obvious in this unit when it is viewed with the naked 

eye or with the binocular microscope. The outlined area is 

shown at higher magnification in figures 3G and 3H. Sample 

has been polished in place with diamond abrasive. Photograph (shown actual size) taken at 32 X through a binocular 

microscope in diffuse illumination. 

3F 

FIGURE 3G.-Enlarged view of the area outlined in figure 3F, 3 G 

mixed lithology (XJ, showing details of the overlapping thin 

lenses of inertite and inertinite (light gray to white) in a 

matrix of vitrinite (medium gray). Black areas are mineral 

grains and holes. The area outlined at the right side of the 

photomicrograph is magnified further in figure 3H. Reflected light, oil immersion contrast. 

FIGURE 3H.-Enlarged view of the area outlined in figure 3G 

showing greater details of the mixed lithology (XJ containing inertinite grains and inertite lenses (light gray and white) 

in a vitrinite matrix (medium gray). Exinite is dark gray. 

Black areas are mostly minerals and some holes. Photomicrograph taken with reflected light, oil immersion. 

7 

3H 
FIGURE 4A.-Block sample of bituminous coal showing a por- .,. 

tion of an in-place polished area consisting of alternating 

dark vitrinite-rich and lighter colored exinite-rich microlithotype bands. The arrow in the lower central part of the photograph indicates a megaspore. In the outlined area, most 

white elongate particles are microspores. The tiny white dots 

are iron sulfide (pyrite) particles, readily recognizable under 

the binocular microscope because of their brightness. No. 6 

coal, Webster County, western Kentucky. Photograph 

(shown actual size) taken at 32 X through a binocular microscope in diffuse illumination. 

those of (X2), and those of (X2) are greater than 

those of (X1). Under the AlAS, they can be quantitatively separated and classified by different grayvalue intervals (Chao and others, 1982a, b); on this 

basis, a quantitative megascopic profile of the coal 

sample can be prepared (fig. 5). The uniform 

sample provides a more consistent basis for observation and classification, even if one wishes to continue using brightness for megascopic differentiation of lithotypes of clarain, clarodurain, and 

durain. The modal composition of mixed lithologies generally cannot be determined or described 

without using a petrographic microscope. 

Larger coal units. Coal units larger than lithotypes, such as assemblages or packets of lithotypes, have not been defined or specified by the 

ICCP. Australian petrographers use subsections 

and plies to describe such units in coal profiles (fig. 

6). We prefer to use the following sequence, in 

order of increasing size of lithologic unit: 

1. Microlithotype. 

2. Lithotype or microlithotype assemblage. 

3. Petrographic type-Lithotype assemblage. 

4. Petrographic unit-Packet of petrographic 

types. 

5. Subsection-Packets of petrographic units. 

6. Section-One or more units of subsections. 

In addition to the above nomenclature, the literature contains terms such as splint, attrital, bone, 

impure coal and partings, tonsteins, and so forth 

(American Society for Testing and Materials, 

1980; International Committee for Coal Petrology, 

1963, 1971, 1975). 

FIGURE 4B.-Enlargement of area outlined in figure 4A show- ..,. 

ing details of the microlithotype containing dark microspores in parallel orientation in vitrinite (gray) and scattered 

round framboidal pyrite (white). Photomicrograph taken 

with reflected light, oil immersion. 

8 
FIGURE 4C.-Area on another block sample from the same coal polished in place with 1-~tm diamond (vertical scratches). Thin 

"lines" of cutinite and white areas of iron sulfide (pyrite) are visible in the middle part of the photograph. Note the oval-shaped 

cross section of fusinitized rodlets in the lower part (gray areas rimmed with white). Photographed through the binocular 

microscope at 32 X in diffuse illumination. 

FIGURE 4D.-Enlargement of microlithotype area outlined in figure 4C showing details of thin linear cutinite (dark stringers) 

along which blocky aggregates of iron sulfide (pyrite, white) have nucleated and developed. Photomicrograph taken with 

reflected light, oil immersion. 

9 
Depth in 

meters 

25.55 

KEY 

D Vitrinite Group 

~ Exinite Group 

~Inertinite Group 

I±J Mineral Components 

(1) 

25.60 

Mo (x1)5 (x2)51 (xa4o04 

) )o(X1)4 (x2)22 (xa~4 (x4)ao 

V, E, I, 

Depth,1 Mixed in vol. in vol. in vol. 

inm lithology percent percent percent 

25.583-25.617----- - -(Xt) 88 10 2 

(v)2a (x1)55 (x2)16 (xa~ (X:J 67 12 20 

(Xs) 53 21 23 

25.617-25.630- - - - - - -(Xt) 88 10 2 

(X:J 58 14 (E+M) 28 

(v)3(x1)41(x2)55 (xa)1 

(Xs) 49 28 16 

(X4) 22 18 40 

25.630-25.654- - - - - - -(Xt) 83 13 4 

(X:J 64 18 13 

(v) 10 (x1)27 (x2 )62 (I )1 

(Xs) 49 28 16 

25.656-25.672- - - - - - -(Xt) 89 7 4 

(X:J 61 20 13 

25.70 (Xs) 49 28 16 

25.672-25.689------ -(Xt) 88 8 4 

0 50 100 (X:J 68 18 (E+M) 14 

VOLUME PERCENT 

1 Distance along the drill core from the grormd surface. 

FIGURE 5.-Columnar profile for the portion of drill-core sample shown in figure 2A. Compositions of the petrographic units in 

terms of volume percentages of microlithotypes and mixed lithologies are shown to the right of the column. After the average 

microscopic modal compositions of the mixed lithologies have been determined for the various thickness intervals (see table), 

the VE IM bulk compositions are calculated and plotted across the column. 

OUANTIT ATIVE NOMENCLATURE 

In our methodology, we propose to replace most 

microlithotype and lithotype terms with quantitative symbols such as (V), (E), (I), (M), (S), (X1), (X2), 

and so forth to eliminate the ambiguity of the composition of the component and the long descriptive 

words. In this quantitative megascopic notation, 

(V) represents vitrite or vitrain, (E) liptite, (I) 

inertite or fusain, (M) mineral layers or lenses 

other than iron sulfide, (S) iron sulfide, and (X1), 

(X2), and so forth mixed lithologies. Compositions 

of the mixed lithologies (X1), (X2), and so forth are 

10 

in turn described microscopically in terms of V, 

vitrinite; E, exinite; I, inertinite; and M, optically 

resolvable mineral fragments. The volume percentage of each component is expressed as a subscript. 

This system, discussed further below and described in detail by Chao and others, (1982a, b), is 

used to generate columnar profiles such as that in 

figure 5. 

We also need to describe coal by its physical and 

chemical properties. Rank, color, luster, texture, 

bulk density, structural terms, ash, and chemical 

characteristics all should be included in a good coal 

description. 

in

pen 
CATEGORIES AND DEGREE OF DETAILS 

OF MEGASCOPIC AND MICROSCOPIC 

COAL DESCRIPTION 

As mentioned above, the objectives of coal description vary depending on the purpose of the 

investigation and on the information required by 

the user. Therefore, details of description and emphasis will vary accordingly. 

The range and categories of details of coal 

description are as follows: (1) field description; 

(2) first-round lab megascopic description; (3) 

second-round lab description supplemented by 

microscopic description; and (4) detailed and refined description, with additional data from chips. 

Category 1 entails a brief field description made 

by using the naked eye or a hand lens and terms 

such as vitrain, fusain, and partings. It serves a 

limited purpose: locating the number of partings 

that are boundaries of megascopic units and that 

may be traceable in the field. This infortnation is 

minimal. 

Category 2 involves study with the binocular 

microscope of block or drill-core samples in the laboratory after the samples have been ground and 

polished with 800-grit abrasives (figs. 2A, 2B). If a 

strip 1 to 2 em wide along one side of the sample is 

polished further by an in-place polishing procedure 

using diamond abrasives (appendices 1 and 2), 

what one can see under the binocular microscope 

will be greatly improved. This first-round laboratory megascopic description is carried out without 

any supplementary study by petrographic microscope. Resolution, depending on the quality of the 

binocular microscope and illumination, can be as 

good as 10 microns. Under this condition, one can 

describe the entire coal bed in great detail (see appendix 3 for the kind of details to be recorded and 

described). 

Category 3 differs from category 2 in that it includes supplementary microscopic description, 

particularly of fine-grained mixed lithologies that 

are not easily resolved under the binocular 

microscope. After in-place polishing, anything 

that is not resolved clearly by megascopic study 

can be observed under the petrographic 

microscope by dry or oil-immersion objective 

lenses. Although microscopic study involves a 

great workload, selective sampling based on the 

first-round observations is the key to reducing the 

number of areas to be studied at higher magnification (appendix 1). 

11 

Category 4, still more detailed, requires that 

chips of particular lithotypes or microlithotype 

assemblages be taken for bulk specific gravity 

determination. (This step could be included in 

category 3 if desired.) Such chips are later made 

into polished thin sections for study in both reflected and transmitted light as well as for electron 

microprobe analysis if desired. The details observed in this manner plus the quantitative megascopic and (or) microscopic analysis using an 

AlAS (or point counting) provide a complete 

characterization. Such details of information are 

aimed at solving a specific problem or are needed 

for facies analysis, which requires a highly interpretive approach. 

FIGURE G.-Petrographic profile of the Permian Garrick seam 

of Australia, modified from Smyth (1970), showing the distribution of V +C (vitrite plus clarite), I (intermediate), Du 

(durite), and Fu (fusite) divided into plies and subsections. 

(/) 

z 

0 

- E ~ 

u F UJ 

(/) 

m G 

~ 

(/) H 

J 

I 

0 50 

v + c 

ROOF 

FLOOR 

I I ---1---.-1 -..,.,--

0 50 0 50 0 50 

I Du Fu 

MICROLITHOTYPE CONTENl; 

IN VOLUME PERCENT 

(/) 

w 

...J 

a.. 

1-

(/) 

-

a: 

w 

1-

u 

ct 

a: 

ct 

I 

u 
TYPES OF DESCRIPTIVE INFORMATION 

REQUIRED FOR DIFFERENT PURPOSES 

COAL CHEMISTRY AND TECHNOLOGICAU Y 

RELATED INFORMATION 

Using coal for coking or for steam coal requires 

knowledge of the rank, the modal composition, and 

the sulfur and ash content of the coal. Describing 

the coal profile in terms of VEIM and pyritejs pertinent because the amount of vitrinite- and exinitegroup macerals present affects caking and expanding properties, and the amount of inertinite affects 

the strength of the coke. Such information is useful also for blending different coals for coke 

making. 

Besides knowledge of pyrite and mineral abundance and distribution in the coal based on petrographic data, chemical, plasticity, and fusion characteristics are supplemental data required for such 

applications. 

COAL WASHABIUTY AND PREPARATION INFORMATION 

Washability and preparation of coal depend on 

the size, abundance, and distribution of pyrite and 

other minerals in the coal. Information on bulk 

specific gravities of specific lithologies is particularly useful for guiding processing based on 

different specific gravity cutoffs in the preparation 

plants. The success of coal preparation is critical 

not only to the particular use of the coal for blending, for coal conversion, or for sale but also for predicting the extent of pollution after burning. 

COAL-BED PROFILES 

Information regarding the coal "seam" profile 

also is pertinent to mining problems. For example, 

knowing the position of shale partings or the frequency of mineral-rich bands can aid in selecting 

the type of mining machine or mining methods to 

be used. 

INFORMATION RELATED TO GEOLOGIC PROCESSES 

Information related to geologic processes not 

only shows the percentage of good-, medium-, or 

poor-quality coal in a coal "seam" or coal bed but 

12 

also helps to reconstruct or interpret depositional 

and (or) geochemical environments. This description, broadly referred to as coal-facies characteristics, is perhaps the most important element in constructing predictive models that show possible 

correlation of coal-bed thickness and quality variations. It requires the most detailed information on 

lithologic characteristics as well as phyteral 

characteristics. 

INFORMATION FOR COAL-BED CORRELATION 

For possible coal-bed correlation, we need both 

detailed lithologic and phyteral information. 

Smith (1962) and Kutzner (1967) have already 

demonstrated the usefulness of such detailed 

petrographic information, as figures 7 and 8 show. 

SAMPLING AND SAMPLE COLLECTING 

TECHNIQUES 

The scheme for sampling a single coal bed or a 

series of coal beds in a coal field or basin should be 

problem oriented. Samples should be collected 

when exposures are fresh and available. Sample 

collection should be iterative to fill the gaps of information needed. 

The types of samples to be collected can be 

grouped into two major categories: 

1. Channel samples of a whole coal bed or of 

benches. 

2. Complete drill-core or block samples representing the columnar stratigraphic section of 

the whole coal bed. 

A single channel sample of a whole coal bed 

gives its average composition. The advantage of 

such a sample is that the method of collecting it is 

quick and simple (Schopf, 1960). If the coal bed 

consists of distinct benches, then bench channel 

samples need to be collected. The major disadvantage of collecting channel samples of a whole coal 

bed is the loss of stratigraphic information representing both petrographic type and facies changes 

of the coal bed. Even if bench channel samples are 

collected, the benches may not have been selected 

correctly, and variations within a bench are lost~ 

One further serious disadvantage is the fact that, 

if thin partings such as millimeter-thick clay-rich 

bands occur anywhere in the coal bed, they are included in the channel sample for all chemical 
rn 

a: 

w 

~ 

w 

~ 

i= 

z 

w 

u 

~ 

en 

rn 

w 

z 

~ 

u 

~ 

~ 

DISTRIBUTION OF MICROLITHOTYPES 

195 

190 

185 

1.80 

175 

170 

165 

160 

155 

150 

145 

140 

135 

130 

I 

125--J I 

I I 

I I 

I I 

=~:: ..... ::f_j:_ ..... :~.: ...... . 50 0 25 50 75 100 I I I I I 

0 /. vi trite 

10075 50 25 0 

I I I I I 

•kclorite 

100 75 50 25 0 

I I I I I 

1. durite 

0 25 50 75 100 

I I I I I 

•t. fusite 

100 75 so 25 0 

I I I I I 

•1• ~h~~eshole 

RELATION BETWEEN MICRO· 

LITHOTYPES & SELECTED 

SPECIES OF MIOSPORE 

•1. vi trite ~ clori te 0 20 .a 60 10 100 

I I I I I I I I I I I 

100 10 60 .. 0 20 0 

I I I I I I I I I I I 

l. desmoinensis 

•J.of P. minutus c. C. kosonkei ---

D. sphoerotriollC)uloris 

~Carbonaceous shale 

FIGURE 7.-Coal-bed profile showing correlation of microlithotype and miospore distribution of a Carboniferous coal from Great 

Britain, modified from Smith (1962). 

13 
Cl) 

a: 

~ w 

~ 

F 

z 

w 

u 

~ 

~ w 

0 

..... 

::... 

EASTERN 

70-

10-

90-

Macroscopic seam section 

Lithotypes: 

D vitrain 

E£m c/arain 

- durain 

~ fusain 

~ vitrain with fusain 

- durain with fusain 

~ carbonaceous shale 

2 3 4 5 

Microscopic analysis of the 

seam section 

Micro/ ifhotypes: 

~::j fusite 

D vitrite 

IJ!!\ clorife 

- duroclorite 

~ clorodurite 

- durite 

lf~::t.:;j corborgilite 

8:~~=3 clayey dirt 

J;,;.;.;v;} corbank~rit~ 

1}:•:•:•:1 corbopyrite 

6 

Symbols of the syngenetic 

minerals: 

I /sofattd occur~tnc• up to-"' 

Frtqutncy of ~~n:;:~ f:~~~ 

Mintral content.s abovt•10 Yo 

Th•fr•quoncy of lh• syng•n•lic min•rals is oslimaled and staled by lh• num~r 

of corrosponding symbols 

2 3 4 5 

5() 

FIGURE 8.-Coal-bed profile showing the use of microlithotype distribution for correlating the easoom and wesoom parts of the 

Wilhelm coal bed, Germany (modified from Kutzner, 1967). For each section of the coal bed, the columns show (1) lithotypes, 

(2) syngenetic minerals, (3) crassispores, (4) percentage variations of fusioo, vitrioo, clarioo, duroclarioo, clarodurioo, and durioo, 

(5) vertical variations of the percentage of fusioo, and (6) vertical variations of clarodurioo plus durioo. 

100 

WESTERN 

6 

50 100% 
analyses. Because clays provide sites for many 

trace-element associations, the total picture of the 

trace elements in the coal itself may be drastically 

distorted or very misleading. If the partings can be 

removed by washing, the chemical data obtained 

from channel samples could affect seriously the 

prediction of pollution problems depending on 

whether washed or unwashed coals are to be used. 

Drill-core or block samples that represent the entire coal bed are necessary to provide the history of 

stratigraphic, facies, and quality changes and variations during the entire accumulation of the coal 

bed. Indications of the depositional and geochemical environments will be recorded in these columnar samples. Columnar samples represent the total 

history of sedimentation of a coal bed; this history 

varies with the transgression and regression of 

water bodies and with the accumulation of plant 

materials themselves. It is, of course, important to 

understand the sedimentary surface of the basin 

on which the peat precursor of the coal accumulated. This sedimentary surface defines a 

depositional environment. As a general rule, for 

autochthonous deposition, approximately 1 mm of 

coal accumulates in 30 years (carbon dating indicates that approximately 1 ft of peat is deposited 

in a thousand years). Therefore, for autochthonously deposited coal, a 10-ft-thick coal bed represents about 100,000 years of depositional history. 

The stratigraphic history of 100,000 years can be 

revealed only by the coal bed and the coal facies 

that it represents. The roof or sediments overlying 

the coal bed generally represent a drastic change 

in the energy level of the water body that caused 

the accumulation of organic matter to cease. 

Therefore, variations of coal thickness and quality 

are influenced by the bottom of the basin and by 

the actual products of organic accumulation. 

Neglecting the description of the stratigraphy and 

facies variation of a coal bed can never be justified. 

Traditionally, columnar (block or core) coal 

samples have been used for coal-bed correlation 

and related studies. If drill-core samples are not 

available, many geologists shy away from collecting block samples instead of channel samples 

because they fear that it will be too time consuming. The most common hand, pick, and chisel 

method of collecting such samples is a tedious and 

time-consuming process, but it will continue to be 

used until a better and more mechanized way has 

been devised and tested successfully. We are interested in any improved technique for collecting 

15 

block samples under a high wall of a strip mine or 

from underground mines where no drill-core 

samples are available. Figure 9 shows a yet untried and unproven plan for collecting a columnar 

block coal sample suggested by James Currens 

(personal commun., 1982) of the Kentucky 

Geological Survey. It is a plan view looking down 

from the top of the coal bed. Two troughs, each 10 

to 15 em wide and on either side of a columnar 

sample 10 to 20 em wide, could be cut by a 

gasoline-driven masonry circular saw. The 

material from the troughs would constitute the 

channel sample or bench channel samples if so 

desired. While the vertical coal face is held in 

place, either by heavy aluminum foil or by a coat of 

plastic material, two angled cuts would be made to 

intersect behind the coal column to remove it. 

The next key question is how to generate a wellplanned, realistic sampling scheme. As mentioned 

before, the sampling design should be problem 

oriented. The coal geologist plays a key role not 

only because he is familiar with the coal geology 

and knows where to collect good, fresh coal 

samples but also because he can outline the problems that the sampling scheme will be aimed at 

solving. 

We realize that the coal geologist is more than 

fully occupied while he is mapping and measuring 

sections in the field. The coal samples, in any case, 

are best collected at a different time by anyone 

FIGURE 9.-Proposed method of obtaining a columnar sample 

of a coal bed. Two troughs or channels 10 to 15 em wide are 

cut and removed on each side of the column as a channel 

sample. Two 45 o cuts are made with a masonry saw to remove the columnar sample, which is held intact either by 

heavy aluminum foil or by the application of plastic cementing materials. 

troughs 

t 

column sample 
trained to do so. We propose that the coal geologist accurately designate the location in the coal 

bed to be sampled. Both a channel sample and a 

columnar sample should be collected as described 

above. We propose that only a brief description of 

the sampling situation be prepared in the field and 

that the columnar sample have its thickness intervals clearly labeled and be brought back to the office or laboratory to be described. The sample 

should be split, ground flat, and polished with 

800-grit abrasive before being described under a 

well-lighted binocular microscope. The time required to describe the coal samples should be a 

part of the office work schedule. The amount of 

time to be spent depends on the problem to be 

solved or on the priority set by the coal geologist 

as to the role of the coal description in his report on 

assessment of the coal resources. 

A realistic sampling scheme should be problem 

oriented and take . advantage of fresh exposures 

when they are available. We also recommend starting with widely scattered samples. Samples should 

be studied at the end of the first field season; on 

the basis of the megascopic descriptive information gained from this first st1Jdy, the sampling pattern should be further filled in to cover lateral distribution variations. Depending on the region and 

the ·complexity of the coal-bearing formation and 

tectonic setting, sampling schemes and numbers 

of samples required will vary and should be 

adaptable. 

EXAMPLES OF PAST AND CURRENT 

-METHODS OF COAL DESCRIPTION 

The first and most commonly used field description is one using terms proposed by Stopes (1919) 

such as vitrain, clarain; durain, and fusain. 

Thiessen (1920) used splint coal, semisplint, attritus, anthraxylon, and bright coal. Schopf (1960) 

recommended using vitrain, fusain, and attrital 

and impure coal and paying special attention to 

the thickness and spacing variation of vitrain 

bands. This approach serves certain field reference 

purposes. Although this kind of description makes 

all coal beds sorind similar, the number of partings 

may be different. The information so conveyed 

tends to be minimal. 

An example of a more informative description is 

the Australian coal "seam" or coal-bed profile, 

which gives· details on the abun4ance of various 

lithologic types on the basis of combined megascopic and microscopic analysis. Figure 6 is such a 

profile of the Garrick seam or coal bed taken from 

Smyth (1970). The profile was shown in nine subsections and four columns . representing their 

microlithotype contents. Total thickness of the 

coal bed was about 90 em. Smyth (1970) grouped 

the subsections into four characteristic "plies" 

and interpreted the plies as typically representative of a depositional environment. In this present 

example, the first subsection J (no. 1 ply) and E 

and D (no. 3 ply) are the best coal; subsections H, 

G, and F represent another ply. Subsections A, B, 

and C, very similar to one another compositionally, are grouped as the fourth ply. This method of 

representation in describing seam or coal-bed profiles was used for standard petrographic profiles of 

the Permian coal beds of New South Wales and 

Queensland, Australia (Smyth, 1970). One hundred and five coal beds so described were used for 

cyclicity analysis (Smyth and Cook, 1976). Certain 

coal beds of a certain age are represented by particular characteristic ''seam'' profiles. The met4od 

of presentation in figure 6 is a good demonstration 

of the usefulness of megascopic and microscopic 

lithologic information in correlating and determining coal-bed profile characteristics. The representation of the intermediate types is ambiguous, 

however, and could be interpreted wrongly. 

A second example is given by Smith (1962), who 

described and correlated the statistical data on 

species of microspores and the lithologies of Carboniferous coal beds of Great Britain. In figure 7, 

Smith shows in three columns the lithologic variation of a certain coal bed. The percentage of vitrite 

is on the left and clarite on the right of the first column. The second column shows the percentage 

variation of the sum of duroclarite and clarodurite 

on the left and that of durite on the right. The 

· third column shows the percentage variation of 

fusite on the left and that of carbonaceous shale 

and shale on the right. Subdivisions of this coalbed profile are located at thicknesses of 61, 131, 

146, and 194 em, on the basis of .both the lithologic 

characteristics and the spore content statistics. 

The coll.unn on the far right shows the relation between microlithotypes and selected species of miospores. As an example, the distribution of abundance of Lycospora pusilla and L. brevijuga follow. 

closely the variation in abundance of vitrite plus 

clarite. Smith has demonstrated the good correlation of microlithotypes and biological phyteral 

16 
spore abundance statistics, which are both useful 

for coal-bed correlation purposes. One problem 

with the detailed quantitative information on the 

microlithotypes presented in Smith's approach is 

that it requires three columns. Another possible 

problem with this type of description is that the 

terms clarodurite and duroclarite are not only ambiguous but also, like the intermediate category 

used by Smyth for Australian coals, possibly erroneous because high-exinite duroclarites and 

clarodurites are not common microlithotypes in 

most bituminous coals. 

A third example is a much more detailed presentation of the macroscopic (megascopic) and 

microlithotype composition of the Wilhelm coal 

bed of Germany by Kutzner (1967). As shown in 

figure 8, the left-hand column is a megascopic profile description using terms such as vitrain, 

clarain, durain, fusain, impure coal, and so forth. 

Kutzner then uses a set of microlithotype terms to 

characterize the microscopic lithologic characteristics of the Wilhelm coal bed. The second column 

shows the abundance and distribution of syngenetic minerals; the third column shows the percentage variation of fusite, vitrite, clarite, duroclarite, 

clarodurite, and durite. The fourth column shows 

the vertical variation of the percentage of fusite 

and the fifth column the variation of clarodurite 

plus durite. Kutzner certainly demonstrates that 

microlithotypes can be used successfully for correlating parts of the coal bed several kilometers 

apart. The information so presented, however, is 

rather difficult to follow, and one needs to correlate the microscopic description with the megascopic description. 

One of the most recent examples of megascopic 

description of coal was given by Daniel and Cole 

(1982) on the Mammoth coal seam in the Bull 

Mountain Basin of Montana They follow the 

method of Cameron (1978) and use the following 

lithotype terms: vitrain, bright clarain (with or 

without pyrite), dull clarain (with or without 

pyrite), durain, durain with fusain, fusain, pyrite, 

impure coal, and shale. Our recommended methodology retains the lithotype terms of vitrain and 

fusain and substitutes for various clarains and 

durain the mixed lithologies having more specific 

modal compositions in terms of major maceral 

groups and minerals. 

The preceding examples demonstrate the usefulness of detailed microlithotype information for 

coal-bed correlation and characterization. Our goal 

17 

is to improve the speed of getting such detailed 

petrographic information and to present the detailed information in readily understandable and 

useful terms. 

PROPOSED METHODOLOGY AND 

RECOMMENDED PROCEDURES FOR COAL 

AND COAL-BED PROFILE DESCRIPTION 

BASED ON QUANTITATIVE PETROGRAPHY 

The objectives of the proposed methodology and 

recommended procedures for coal description 

based on quantitative petrographic information 

are reviewed below: 

1. To improve the speed of obtaining quantitative 

petrographic information. 

2. To eliminate the ambiguity introduced by 

many of the quantitatively less precise 

microlithotype terms. 

3. To use visual estimates for obtaining quantitative petrographic data, calibrations being provided as necessary by the use of the 

AlAS. 

4. To reduce the amount of duplicative microscopic observations in order to drastically 

increase the speed of detailed petrographic 

study. 

5. To render possible comparison of quantitative 

coal descriptions (both megascopic and 

microscopic) by graphic columnar sections 

and plots on ternary diagrams. 

CONDITIONS AND EXPECTATIONS OF MEGASCOPIC 

OBSERVATION, EXAMINATION, AND DESCRIPTION 

Two aspects that may greatly improve the completeness and speed of petrographic description of 

coal quite possibly may have been overlooked or 

may not have received their due emphasis in the 

past. One aspect is the necessity and advantage of 

sample preparation before megascopic observation 

in the laboratory; the second is the resolution and 

amount of specific information on coal components 

observable or identifiable under megascopic conditions by using a 32 X binocular microscope. 

Before preparing a portion of the block sample 

for megascopic examination, we recommend dividing the sample in half by using a band saw 

equipped with a continuous-edged tungsten carbide blade without liquid lubricant. One-half of the 
sample is reserved for chemical and palynological 

analysis, and the other half is for petrographic 

study. 

The procedure for preparing the coal sample for 

megascopic examination is given in appendix 1. 

Contrary to the usual practice, where megascopic 

examination is conducted on naturally fractured, 

irregular surfaces of coal, we strongly recommend 

preparing the coal sample to produce a uniformly 

flat surface that not only would reveal clearly the 

constituents in the coal but also would insure that 

the differences in the light scattering and reflecting properties of the coal components would not be 

distorted by the shadows and angles of irregular 

surfaces. To attain this uniformity, we recommend 

that the entire flat surface of the coal sample be 

ground and partially polished with 800-grit 

abrasives. The 800 grit is chosen because (1) the 

polishing can be accomplished quickly, (2) details 

of the coal are well revealed, and (3) the surface 

produced will not reflect the illuminating light 

source under the macroscopic setup of the AlAS. 

In addition, we recommend that a strip 1 to 2 em 

wide, covering the entire length normal to the 

banding structure of the coal sample, be highly 

polished by using the in-place polishing technique 

described in appendix 2. 

Photographic documentation of each series of 

coal-bed samples is desirable as a record for annotation and classification of lithologic variations. 

For observatio~, we also recommend using a 

ring light with the binocular microscope for uniform illumination. The sample can be viewed flat 

lying or tilted (using a hemisphere rotating substage). Normally, there is no need to tilt the sample unless one wishes to change the angle of illumination for comparing the light properties or for 

improving the contrast of certain features. The 

resolution at 32 X magnification is slightly better 

than 10 microns; that is, any component or particle 10 microns or larger can be distinguished 

under this binocular microscope setup on the basis 

of its shape, texture, or light properties. 

MEGASCOPIC RECOGNITION OF MACERALS AND 

MICROLITHOTYPES 

By observing the combined size, shape, texture, 

and light-dispersing and reflecting properties, we 

can generally distinguish or identify the following 

components: (1) pyrite or mineral grains (quartz or 

18 

clay) down to approximately 10 microns (figs. 4A, 

4C); (2) vitrite (figs. 2A, 2B, 3A, 3F, 4A, 4C), which 

appears dark, and inertite, which appears bronzy 

gray (fig. 3F), particles, lenses, or lamellae; (3) megaspores (fig. 4A), microspores (only by shape) (fig. 

4A), and cutinite of the exinite group (fig. 4C); 

(4) fusinitized rodlets (fig. 4C); and (5) microlithotypes of mixed lithologies (figs. 3A, 3F, 4A, 4D). 

What are usually not readily distinguishable or 

identifiable megascopically are semifusinites and 

fine-grained inertinite such as micrinite. The semifusinites can be confused easily with aggregates of 

exinites. Both contribute to the lighter color of 

microlithotypes of mixed lithologies under the illumination conditions for megascopic observation. 

The next stage of investigation is to check 

microscopically what is megascopically discernible 

but unidentified, since the sample is prepared for 

microscopic observation as well. This step will improve the petrographer's ability to make better 

megascopic observations and identifications. 

BRIDGING THE GAP BETWEEN MEGASCOPIC AND 

MICROSCOPIC OBSERVATIONS 

The ability to classify microlithotypes or assemblages of microlithotypes under the binocular 

microscope can be improved by examination under 

the AlAS macroscopic setup. The binocular examination and AlAS gray-value intervals are used 

jointly for classifying categories of mixed 

lithologies. Consistency in classification is a basic 

requirement; correlation between macroscopic 

AlAS analysis and megascopic classification and 

microscopic description (AlAS analysis) of the 

classified mixed lithologies must be completely 

free of ambiguity. A few weeks of training will 

greatly help the operator-observer in making the 

transition from megascopic observations to microscopic observations. 

Our experience, although as yet somewhat 

limited, has shown the potential usefulness of a detailed megascopic description of a coal bed accompanied by a fair amount of photographic documentation and has demonstrated that the amount of 

supplementary microscopic description required 

can be reduced. 

PROCEDURES FOR FIRST- AND SECOND-ROUND 

LABORATORY MEGASCOPIC DESCRIPTION 

After the sample is polished with 800-grit 

abrasives, a first-round binocular observation can 
be accomplished quickly by using an ocular micrometer for visual quantitative estimates of various microlithotype assemblages and lithotypes. 

The lower limit of 2 mm suggested in step 3a of 

appendix 1 for delineating microlithotypes is intended for coal beds less than 3 m thick. A cutoff 

limit greater than 2 mm may be chosen for describing coal beds of much greater thickness. A 

suggested checklist of what to observe and describe for various types of information is given in 

appendix 3. This list may be adjusted accordingly 

for different coals. 

The purpose of step 4a in appendix 1 is to demarcate thickness intervals of petrographic types that 

appear to be different from adjacent units in relative abundance of microlithotypes and lithotypes. 

The number of meaningful subdivisions of 

mixed lithologies in a coal is determined by the 

observer-operator on the basis of the amount of 

detail desired. The fewer the number of details, the 

quicker the description can be accomplished. We 

recommend that, on the basis of the ease or the 

sharpness of natural distinctions, the fewer mixed 

lithologies to be described microscopically, the 

better. 

If several mixed lithologies are subdivided 

megascopically, their relative thickness intervals 

should be obtained by micrometer traverse under 

the binocular microscope. If the macroscopic 

AlAS is available, the resolution or the minimum 

width of the mixed lithologies to be classified is 

0.5 mm. If the AlAS is not available, then the classification of mixed lithologies is based solely on 

binocular examination. The observer-operator can 

then have the flexibility of deciding what the 

minimum width of units of mixed lithology should 

be. Depending on the nature of the coal, for some 

autochthonous Pennsylvanian age eastern U.S. 

coals, where the coal-bed thickness is generally 

less than 3 m and where the coal is generally finely 

laminated and well banded, one may choose 1 or 

2 mm as the minimum width for traverse measurement. For some Mesozoic western U.S. coals, particularly those of allochthonous origin having coalbed thicknesses greatly in excess of 3 m, the bands 

of different lithotypes or mixed lithology are generally thicker. In such cases, one may set a 

minimum width of 5 mm or even 1 em for entities 

of mixed lithologies to be , measured by the 

traverse method under the binocular microscope. 

At the end of the first-round laboratory description, the entire coal-bed profile is demarcated and 

19 

described. The distribution of lithologic types 

greater than 2 mm thick is shown on the columnar 

section in terms of vitrite or vitrain, fusite or 

fusain, mineral- or pyrite-rich bands, and mixed 

lithologies (X1), (X2), and (X3), and so forth (consisting of assemblages of microlithotypes in alternating or overlapping lamellae or lenses between 0.5 and 2 mm in thickness). The columnar 

coal-bed profile, completed after the first-round 

laboratory description, is comparable in informational content to the combined microscopic and 

megascopic description shown in the example of 

an Australian Permian coal discussed above and 

shown in figure 6 (Smyth, 1970). 

The major function of the second-round laboratory description is to provide the quantitative 

microscopic average modal composition of each 

mixed lithology by using either point count techniques or, if available, the AlAS method. This 

method is described in steps 5 through 7 in appendix!. 

If the observer-operator decides to have only one 

single mixed lithology that ranges in composition 

between the end members of vitrite or vitrain and 

fusite or fusain, then an average modal composition for this one mixed lithology is obtained. We 

should keep in mind that any vitrite or fusite 

greater than 0.5 mm in extent (resolved by AlAS 

macroanalysis) is not a part of a mixed lithology, 

whereas those smaller than 0.5 mm are included in 

the microscopic modal analysis of the mixed lithology. The discrete vitrite or vitrain, fusite or fusain, 

and mineral lenses or bands greater than 0.5 mm 

in dimension are treated as individual components 

scattered within or interlayered between lenses or 

layers of the mixed lithology that acts as the surrounding "matrix." This method entails a 

minimum amount of microscopic analysis, so we 

recommend it. The "average" modal composition 

of the mixed lithology, however, may vary stratigraphically within the coal bed. Differences in 

composition should be recorded as desired. This 

type of description is comprehensive. No further 

microscopic analysis is required. 

If more than one type of mixed lithology is discerned-for example, an exinite-rich mixed lithology (X1) (analogous to clarite or duroclarite), an 

inertinite-rich mixed lithology (X2) (representing 

clarodurite or some undefined intermediate type), 

and an inertinite- and mineral-rich mixed lithology 

(X3) (corresponding to durite)-then great care 

must be exercised to avoid uncertainty or ambigu-
ity during microscopic analysis of these megascopically classified mixed lithologies. If the 

operator is inexperienced, we recommend the use 

of photographs and medium-scale photomicrographs to make certain that the area analyzed 

microscopically is actually the one classified megascopically under binocular examination and quantitatively analyzed under the AlAS macroscopic 

setup. 

When more than one mixed lithology is discerned, another constantly encountered problem is 

that the criteria for classification or boundary between two or more mixed lithologies greater than 

0.5 mm must remain consistent and unchanged. 

Furthermore, this procedure should be followed for 

each stratigraphic or thickness interval for the entire coal bed where the average modal composition 

of a particular mixed lithology changes. These precautions are necessary for beginners. Such possible mistakes can be avoided easily through experience or the exercise of a certain amount of care 

when areas for microscopic analysis are selected. 

There is rarely any need, in our experience, to have 

more than three categories of mixed lithologies in 

most coals as a data base for detailed coal-facies 

analysis. 

I , 

Once the average modal compositions of all the 

mixed lithologies have been obtained either by 

point count or by the use of AlAS, step 9 of appendix 1 can be accomplished easily by using a computer program, so that the total amount of the major maceral groups and observed minerals in any 

stratigraphic or thickness interval of the coal-bed 

profile is described and outlined clearly. This procedure completes the second-round description. 

METHODS OF AlAS QUANTITATIVE ANALYSIS 

As we have already indicated, the AlAS is an invaluable tool for rapidly obtaining quantitative 

information on microlithotype and lithotype abundances. Figure 10 is a flow diagram of our AlAS, 

figure llA shows the overall configuration of the 

equipment, and figure liB shows the macroscopic 

setup and a block sample of coal placed under a circular fluorescent lamp below the TV camera 

Under the macroscopic AlAS setup, a thickness 

interval of about 5 em can be analyzed at one time. 

The different types of microlithotype or lithotype 

or mixed lithologic units can be classified and distinguished according to their light properties by 

W TELEVISION Ajo 

M=A=C~=RO=V=I=EW=E~ ....... ER-.. --.~-_. .. _CONV.~R. ijj - , f + .I I • • 'UG~ MICROSCOPE g 

KEYPAD 

-

• . 

IMAGE 

PROCESSOR 

FIGURE 10.-Flow diagram of the Joyce-Loebl MAGISCAN automated image analysis system. Modified from the equipment 

description brochure of the manufacturer. 

20 
.. 

FIGURE llA.-Overall configuration of the MAGISCAN automated image analysis system showing, clockwise from the 

left, (1) the computer terminal, (2) the console containing the 

minicomputer (left), the TV monitor screen, the keypad, the 

light pen, and (inside the cabinet) the microprocessor and 

analog-to-digital and digital-to-analog converters, (3) macroscopic setup for analysis of hand samples and photographs, 

and (4) the TV camera, positioned on the petrographic 

microscope. 

<1111 FIGURE llB.-Setup for macroscopic analysis of hand samples with the MAGISCAN automated image analysis 

system. From the top: TV camera with zoom lens, fluorescent ring light, and partially polished split-core coal sample. 

Floodlights are used when photographs are to be analyzed. 

21 
scattering and diffuse reflection. These properties 

are measured in terms of a range of 64 gray values 

for our AlAS instrument. The light-contributing 

properties of macerals, singly or in aggregates 

under the AlAS macroscopic illumination setup, 

are generally as follows. Vitrinite, vitrite, and 

vitrain are dark. They have a gray-value interval 

ranging from 0 to less than 11. Individual exinites 

or small particles of semifusinite and fusinite of 

the inertinite group, although they are not resolved megascopically, contribute to the light 

properties and make a gray-value interval higher 

than that for vitrite. Thu~, a lithotype consisting 

of mixtures of substantial vitrite and various 

amounts of exinite and inertinite could have gray 

values ranging from 10 to 20 or from 20 to 25 as 

the amounts of exinite and inertinite increase. 

Nearly pure fusite or fusain lenses or bands range 

in gray values from about 25 to 30. As mineral content increases, the gray values increase to greater 

than 30 or 40. Iron sulfide minerals have gray 

values above 50. Therefore, according to the grayvalue intervals, the various types of microlithotypes, lithotypes, and mixed lithologies in 

bituminous coal can be distinguished generally 

and described quantitatively. 

The image on the 14-in. TV monitor screen consists of 512X512 picture points (pixels). The total 

number of pixels registering a particular grayFIGURE 12A.-TV screen view of a split core polished with 

800-grit abrasive illuminated by a fluorescent ring light. 

Vitrite-rich areas appear dark, fusite and mineral-rich areas 

appear bright, and mixed lithologies appear intermediate 

gray. Sample of I coal from the Emery Coalfield, central 

Utah. Area inside white frame is 5.5 X5.5 cm2

• 

22 

value interval can be calculated quickly by the 

minicomputer as a percentage of the total area 

analyzed and therefore as volume percent (Chayes, 

1956). In the macroscopic analysis mode, after 

classification of the various lithologic categories 

observed repeatedly for the entire coal bed, 

analysis can proceed rapidly. For each 5-cm 

thickness interval (figs. 12A, 12B), the normal 

time required for an analysis is about 3 min. 

However, classifying the segmentation of each 

category (assigning of gray-value intervals by the 

operating petrographer) usually requires 10 min or 

more. 

AlAS microscopic analysis of the in-place 

polished strips, polished mounts, or polished thin 

sections follows the same general principle, but the 

analysis is based on gray levels corresponding to 

reflectance from the macerals (figs. 13A, 13B). For 

microscopic analysis, the TV camera is mounted 

on top of a research petrographic microscope using 

xenon lamp illumination. (We also hope to have, in 

the future, an additional TV camera sensitive to 

low-level images in fluorescence, important for 

studying lower rank coals.) 

SELECTION OF CHIPS FOR FURTHER INVESTIGATIONS 

To return to step 6, appendix 1, the major objective for removing from a block sample a chip 

FIGURE 12B.-Segmentation of vitrite-rich areas (covered by a 

white overlay) in the same field shown in figure 12A. At the 

right edge of the screen, a gray-level "thermometer" display 

shows the gray-value interval assigned to vitrite. 
FIGURE 13A.-TV screen view of an area in a polished block 

of No.6 coal from Webster County, western Kentucky, in incident light. Gray values are displayed for exinite (6-11), 

vitrinite (22-27), and inertinite (37-41). Area outlined by 

white frame is approximately 200X200 ~tm • 

greater than (0.5 cm)3 that is representative of a 

particular lithologic type is to obtain further information on its bulk density, modal maceral composition, and chemistry. The first problem is where 

to remove the chip. Careful monitoring by in-place 

polishing can indicate clearly where the chips 

should be removed, so that no ambiguity can occur 

as to what the chip represents. The chip can be 

removed by using a pen knife or a razor blade, but, 

for better control, a thin saw blade should be used. 

The "Certigrav" liquids1 that we use for bulk 

specific gravity determinations on the removed 

chips are organic liquids that are nontoxic and 

that maintain their specific gravity even upon 

evaporation. The specific gravities of the set of 

liquids used are calibrated by pycnometer or 

hygrometer methods, and their refractive indices 

are determined by using a refractometer. Then a 

working curve is constructed relating the specific 

gravities of the series of liquids to their refractive 

indices with a ±0.0002 precision and a temperature correction. This working curve makes it easy 

to determine the specific gravity of a mixture of 

the reference liquids by its refractive index. This 

method is much more rapid than direct specific 

gravity determination for a small amount of liquid. Any coal chip to be tested is dropped in a liq23 

FIGURE 13B.-Segmentation of exinite (covered by a white 

overlay) in the same field shown in figure 13A. At the right 

edge of the screen, the filled region of the gray-level "thermometer" display and the digital values in the upper righthand comer show the gray-value interval assigned to exinite. 

Area outlined by white frame is approximately 200 X 

200 ~tm • 

uid to see if it sinks or floats. If it floats, then a 

much lighter liquid is added until it just begins to 

sink, and the refractive index of this liquid (Rll) is 

determined; then a heavier liquid is added until the 

chip begins to float, and the refractive index of the 

heavier liquid (RI2) is determined. The midpoint 

between RI 1 and RI 2 determines the corresponding 

specific gravity from the working curve and thus 

establishes the bulk density of the chip. The bulk 

density of a chip generally reflects its modal composition, because vitrinite and exinite of a certain 

rank of coal represent the lighter end members of 

the density spectrum, whereas fusinite (which has 

a specific gravity of -1.5) and minerals (which 

have a specific gravity greater than 2.65) represent 

the heavier end of the spectrum. A coal chip having a bulk specific gravity greater than 1.40 generally signifies an impure coal. High-vitrinite coals 

have a bulk specific gravity ranging from about 

1.22 to generally less than 1.30, and coal chips containing various amounts of fusinite and minerals 

range in bulk specific gravity generally from 1.30 

1 Available from American Minechem Corp., C<nopolis, PA 15108. The use of trade 

or brand names does not constitute endorsement of products by the U.S. Geological 

Survey. 
to 1.40. The specific gravity liquid sink-and-float 

method is easy to use and can be used in the field 

for quick tests of coal chips to aid evaluations of 

impure coal versus better quality coal. 

The removed coal chip can also be polished for 

study under the microscope. Its modal composition can be determined quickly by using the AlAS. 

For observing in combined transmitted and 

reflected light, a polished thin section can be made. 

Making a polished thin section of such a small chip 

(those removed are usually about 0.5 em across) requires far less skill and time than making one that 

is 2 to 3 em across. Those who know the benefits of 

using both transmitted light and reflected light 

will appreciate this substantial advantage. These 

polished thin sections provide the opportunity for 

more detailed study of the phyterals (figs. 14A, 

14B) and textures of the chip's components and 

for trace-element analysis of various macerals by 

either the electron or the PIXE microprobe 

methods. 

For correlation between quantitative petrographic data in terms of VE IM and coal chemistry, such chips will and should be chemically 

analyzed. Research in this area is in progress. 

The third round of laboratory description includes all the petrographic information from the 

chips supplemented by photomicrographic documentation of all the mixed lithologies and their 

phyteral characteristics. 

The fourth round of laboratory description deals 

with the interrelationship and association of lithologic types, particularly the presence or absence 

of cyclicity of the various lithotypes, and provides 

the basis for interpretation with respect to depositional environment. Because of the great detail 

directed toward the interpretation of the petrographic description, fourth-round studies are more 

specialized and are to be carried out by coal petrographers and petrologists. They fall in the realm of 

the methodology of petrographic analysis of coal 

facies, a subject for another paper. 

DATA PRESENTATION AND USE 

We have shown examples of coal "seam" or coalbed profiles used for Australian Permian coals by 

Smyth (1970) (fig. 6), for British Carboniferous 

coals by Smith (1962) (fig. 7), and for German coals 

by Kutzner (1967) (fig. 8). For greater ease of comprehension, we recommend the presentation of the 

24 

FIGURE 14A.-Area of vitrite in a polished thin section of 

bituminous coal. Vitrinite-group macerals telinite (with wellpreserved cell structure, upper half of photograph) are labeled T; transitional zone traces of cell structure (adjacent to 

telinite areas) are labeled TC; and collinite (showing no cell 

structure, bottom of photograph) are labeled C. Upper 

Freeport coal, Indiana County, Pa. Photomicrograph taken 

in transmitted light, oil immersion. 

FIGURE 14B.-Polished thin section of commercial cannel coal 

from eastern Kentucky showing alginite (A) (light gray, 

scalloped edges) and sporinite (8) (medium gray, smooth 

margins). Photomicrograph taken in transmitted light. 
coal-bed profile shown in figure 5. For each megascopically demarcated thickness interval, we indicate the relative abundance of the various component lithologic types. Such results are similar to 

the "seam" or coal-bed profiles used for describing 

Australian coals. If the composition of the mixed 

lithologies is determined microscopically, the conversion to the total composition of a thickness interval in terms of VE IM can be carried out (fig. 5; 

step 9, appendix 1). The entire coal-bed profile is 

represented in terms of the detailed lithologic and 

quality variation from bottom to top. 

We can also compare several columnar sections 

side by side. If a large number of such profiles are 

to be compared, however, it is easier to plot the 

total composition of any segment of a coal bed or 

of the entire coal bed on a ternary diagram. Figure 

15, an attempt at such a plot by Strauss and 

others (1976), does not, however, consider the min1/ITRi!oiiTE 

EX IN 

eral component, which is a very important parameter concerning the impurity of the coal. Figures 

16A and 16B are ternary plots, the apices of which 

are represented by vitrinite group V, exinite group 

E, and the combined total of I (inertinite) plus M 

(minerals other than iron sulfide) plus S for iron 

sulfide. The position of a point on such a diagram 

represents the V, E, (I+M+S) composition, 

whereas the solid line or tail of the dot normal to 

side VE of the triangle represents the percent M, 

the dashed line between the crossbar and the dot 

would represent the percent S, and the distance 

from the end of this line to side VE is the measure 

of percent I. We believe that the use of this ternary 

diagram is straightforward and simple. 

The V, E, (I+ M + S) diagram can be used to plot 

the composition of all types of mixed microlithotype lithologies (fig. 16A) and to compare them 

stratigraphically throughout a coal bed. It can also 

Main compositional field of Tertiary coals 

of West Pacific and India (and Upper 

Cretaceous of New Zealand) 

Minor Tertiary coals, principally 

of India 

Main field of Gondwana coals 

Minor Gondwana coals of 

Australia and India 

FIGURE 15.-VEl (mineral-free) ternary diagram comparing petrographic characteristics of Tertiary, Cretaceous, and Gondwana 

coals of the West Pacific and India (Strauss and others, 1976). Reactive component R=vitrinite+exinite. 

25 
be used to plot the average composition (VEIM) of 

various stratigraphic or thickness intervals of a 

single coal bed (fig. 16B) to show the stratigraphic 

variation of composition. If the extent of the thickness interval is important, then different 

symbols can be used ·to illustrate different categories of thickness intervals. For comparison of 

different coal beds, different symbols can be used 

v 

11 

to represent different coal beds on the same 

diagram, or separate diagrams can be prepared on 

transparent overlays. 

QUANTITATIVE COAL-BED DESCRIPTION: 

A NEW DATA BASE 

We suggest that, for most investigations, the 

information gained after the second-round descripKEY: 

• x1 

• x2 

• x3 X X4 

19, 20, 21,22 

-~ .2 

E 

13,14,15,16,1~~8 

~5 23,24,25, 26 

" 

-...,.2 .................... 9 

~ ...........,7,8 19 20 21 22 .:::::---..3 . • . ~10 ..... 

so 

FIGURE 16A.-Recommended ternary diagram for plotting microscopic modal compositions of mixed microlithotype lithologies to 

show stratigraphic variations for a single drill-core sample of a coal bed (Hazard coal, Knott County, eastern Kentucky). Apex V 

represents the vitrinite group; E, the exinite group; and (I+ M +S), the combined total of inertinite plus optically observable 

minerals (other than iron sulfide) plus iron sulfide. The length of each solid line extending from a data point represents volume 

percent M, and the distance from the end of this line to side VE of the triangle represents percent I. Any S present would be 

plotted as a dashed-line segment complementary to M (sulfide was present in this sample only in amounts less than 1 vol. percent). Numbers adjoining the data points identify the thickness intervals numbered sequentially from top to bottom of the coal 

bed. (Intervals 2 to 6 correspond to the thickness intervals included in the columnar profile of figure 5.) Only mixed lithology 

(X1) is present in all intervals; some numbers will be observed to be missing for the other mixed types, which may be present but 

in amounts less than 1 percent. 

26 
"-...13 

v 

1 'o 19 

0 18 

014 .1 

12 4 'e! .... 20 "o24 

~""08 

21 .6 '5 

~10 

KEY 

thickness interval ranges (mm) 

0 2 -10 

• 11- 20 

0 21 - 30 

• ) 30 

..,_23 

'-.2 

'o22 

..... 9 

E I+M+S 

FIGURE 16B.-V, E, (I+M+S) ternary diagram showing average total VEIM compositions for the thickness intervals of the coal 

sample shown in figure 16A. Pure vitrain or fusain bands 2 mm or more in thickness normally should be included in the total 

thickness interval composition calculation. Such bands are omitted on this diagram. 

tion is adequate. The end products are the completed coal-bed profile shown by a columnar 

section, documentation photographs or photomicrographs of the principal coal lithotypes and 

petrographic types, and ternary diagrams of coal 

composition in terms of VEIMS. Such information 

can stand alone for comparison with other sections 

of the same coal bed or other coal beds. If more columnar sections or triangular plots of the same coal 

bed are made, a regional variation picture can be 

constructed. If comparison with different coal 

beds is to be made, clues to possible correlation 

may be established. The methodology and proce27 

dures recommended here use quantitative petrography to provide a new data base on coal beds that 

should facilitate ready comprehension of the coal 

quality and provide a reliable means for coal-bed 

comparison and correlation. 

SUMMARY: THE WHY, WHAT, WHO, AND 

HOW OF COAL DESCRIPTION 

Why describe coal? Any report on coal investigation should convey to the reader the nature and 

characteristics of the coal bed or beds under in-
vestigation. The details and emphasis of such a 

description will vary, depending on the objectives 

of the investigation and on the user of the report. 

It is not a subject that can be avoided. The quality 

and the usefulness of the report depend very much 

on how informative and useful the descriptions · are. 

What should be included in a coal description? 

Appendix 3 gives a check list of what to describe 

for any coal-bed profile. 

Who should be describing the coal? Naturally, 

the investigator, the author of the coal report, or 

anyone trained to assist him. It is somewhat 

mysterious why most coal geologists do not 

describe the coal beds that they are mapping and 

evaluating. 

How to describe coal or a coal bed? Our emphasis is on quantitative coal petrography and 

megascopic description. Our goals in improving 

coal description are to drastically improve the 

speed of getting the descriptive data, to expand 

the usefulness of the informational content, and to 

present the data in a form that can be comprehended easily. 

REFERENCES CITED 

American Society for Testing and Materials, 1980, Standard 

definitions of terms relating to megascopic description of 

coal and coal beds and microscopical description and 

analysis of coal, in 1980 annual book of ASTM standards, 

pt. 26: Philadelphia, Pa, p. 363-366. 

Bates, R. L., and Jackson, J. A., eds., 1980, Glossary of 

geology (2d ed.): Falls Church, Va, American Geological 

Institute, 751 p. 

Cameron, A. R., 1978, Megascopic description of coal with 

particular reference to seams in southern Illinois, in 

Dutcher, R. R. (ed.), Field description of coal: American 

Society for Testing and Materials Special Technical Publication 661, p. 9-32. 

28 

Chao, E. C. T., Minkin, J. A., and Thompson, C. L., 1982a, 

Application of automated image analysis to coal petrography: International Journal of Coal Geology, v. 2, 

p. 113-150. 

__ 1982b, Recommended procedures and techniques for the 

petrographic description of bituminous coal: International 

Journal of Coal Geology, v. 2, p.151-179. 

Chayes, Felix, 1956, Petrographic modal analysis: New York, 

John Wiley, 113 p. 

Daniel, J. A., and Cole, G. A., 1982, Petrography of the 

Mammoth Coal Seam, Bull Mountain Basin, Musselshell 

County, Montana: Utah Geological and Mineral Survey 

Bulletin 118,p.168-178. 

International Committee for Coal Petrology, 1963, International handbook of coal petrography (2d ed.): Paris, Centre National de Ia Recerche Scientifique. [n.p.] 

__ 1971, International handbook of coal petrography 

(suppl. 1): Paris, Centre National de Ia Recherche Scientifique. [n.p.] 

__ 1975, International handbook of coal petrography 

(suppl. 2): Paris, Centre National de Ia Recherche Scientifique. [n.p.] 

Kutzner, R., 1967, Versuch einen weitraumigen Flazgleichstellung mit Methoden der Kohlenpetrographie: GluckaufForschungshefte, v. 28, p. 39-48. 

Schopf, J. M., 1960, Field description and sampling of coal 

beds: U.S. Geological Survey Bulletin 1111-B, 70 p. 

Smith, A. H. V., 1962, The palaeoecology of Carboniferous 

peats based on the miospores and petrography of bituminous coals: Proceedings of the Yorkshire Geological 

Society, v. 33, pt. 4, no.19, p. 423-474. 

Smyth, M., 1970, Type seam sequences for some Permian 

Australian coals: Australasian Institute of Mining and 

Metallurgy Proceedings, no. 233, p. 7-15. 

Smyth, M., and Cook, A. C., 1976, Sequence in Australian 

coal seams: Mathematical Geology, v. 8, no. 5, p. 529-547. 

Stach, E., Mackowsky, M.-Th., Teichmuller, M., 'faylor, G. H., 

Chandra, D., and Teichmuller, R., 1975, Sta&'s textbook 

of coal petrology: Berlin, Gebruder Borntraeger, 428 p. 

Stopes, M. C., 1919, On the four visible ingredients in banded 

bituminous coal: Proceedings of the Royal Society of 

London, v. B90, p. 470-487. 

Strauss, P. G., Russell, N.J., Bennett, A. J. R., and Atkinson, 

C. M., 1976, Coal petrography as an exploration aid in the 

west Circum-Pacific, in Muir, W. L. G., ed., Coal exploration: San Francisco. Miller Freeman, p. 401-447. 

Thiessen, R., 1920, Structure in Paleozoic bituminous coals: 

U.S. Bureau of Mines Bulletin 117, 296 p. 
APPENDIX 1: PROCEDURE FOR LABORATORY MEGASCOPIC DESCRIPTION OF COALBLOCK OR DRILL-CORE SAMPLES 

1. Sample preparation: 

a Labeling of samples to preserve record of stratigraphic interval and orientation represented. 

b. Cutting of sample into two halves, one of which is reserved for chemical and palynological 

analysis. 

c. Grinding and partial polishing (to 800 grit) of other half of sample for megascopic study. 

2. Photographic documentation of prepared samples, recommended for standard coal-bed description; 

optional for others. 

3. Visual and binocular examination: 

a Demarcation of (V), (1), (M), (S), and partings (2 mm thick or more). Entry of data on columnar section. 

b. Documentation of significant structural features observed, such as thickness and repeat pattern of layers, fragmental nature of components, and so forth. (See appendix 3.) 

4. Megascopic quantitative visual estimate of modal composition of microlithotypes and microlithotype assemblages: 

a Make visual estimate of the amount of (V), (1), (M), (S), (XI), (X2), and so on present in any 

clearly marked megascopic petrographic unit by measuring the total thickness intercept 

of each lithology by using a calibrated ocular micrometer. The fraction of a microlithotype, microlithotype assemblage, or lithotype present is that thickness intercept divided 

by the total thickness interval of the megascopic unit. Enter data on columnar section 

(fig. 5). 

b. Where 2-mm (or larger) bands of the same microlithotype or lithotype are closely spaced, 

the petrographer may combine these bands and the intervening microlithotypes and (or) 

microlithotype assemblages into one megascopic petrographic unit to simplify the 

description. 

5. Using in-place polishing procedure, polish a strip 1 to 2 em wide from each block or core sample from 

top to bottom with 1- and 1/4-J,tm diamond abrasives (appendix 2). A very rapid and simple procedure that allows observation of petrographic units in greater detail. 

6. Removal of representative sample chips from (XI), (X2), and others: 

a Determination of bulk specific gravity of removed chips by sink and float "Certigrav" 

liquids. 

b. Optional: Preparation of polished mounts and (or) polished thin sections from the specific 

gravity chips for microscopic examination. 

7. Optional: Visual estimates of microscopic modal analysis of mixed lithologies (XI), (X2), and others. 

8. Addition of the VE IM data for (XI), (X2), and others to the columnar section if available. 

9. Recalculation of total VEIM composition for each demarcated lithologic unit: 

a Plotting of the VEIM data as percentages across the columnar section (fig. 5). 

b. If desired for greater clarity, additional plotting of the data on a V, E, I+ M +S ternary diagram (figs.16A, 16B). 

10. After completion of the entire columnar section, compare the petrographic description and classification with the photographic documentation (step 2) to check for inconsistencies. 

APPENDIX 2: THE IN-PLACE POLISH PROCEDURE 

The objective of this procedure is to obtain quickly a maximum degree of polish for each lithotype area 

on the coal-sample surface. Polishing an entire block sample of coal to a high degree is laborious and time 

consuming because of the large surface area involved. By means of in-place polishing, one can considerably reduce the time required to prepare a small area along the surface of the sample, which is 

amply suitable for detailed megascopic observation and microscopic analysis. The procedure involves 

29 
polishing only a strip, 1 to 2 em wide, on the surface of a block of coal already ground flat and partially 

polished with 800-grit abrasives. The strip can cover any part of the block or its entire length, as preferred. The degree of polish should be as good as that of a polished mount or a polished thin section and 

as scratch free as possible. 

The technique involves the following steps: 

1. Use a stick or rod with a flat end about 1 em in diameter. For convenience, we use a 5-cm-long metal 

bolt having a 1-cm hexagonal or circular flat top surface. Cut a piece of TEXMET2 polishing 

substrate 1 em in diameter backed by pressure-sensitive adhesive and attach it to the flat end 

surface of the rod or bolt. 

2. Charge the TEXMET on the bolt with 1-p.m diamond paste; a small amount of oil is used as the required lubricant and diluent. 

3. Hold the TEXMET-covered surface of the rod or bolt flat against the coal sample from above and 

polish the desired length of the surface, exerting moderate pressure for 20 to 30 s and making 

sure that the flat polishing surface is not tilted with respect to the flat coal surface at any time. 

Keep the TEXMET surface clean; replace, when necessary, to prevent scratches. 

4. Wash the polished surface with soap solution and distilled water, thoroughly removing all the diamond abrasives. Dry with compressed air. 

5. Check the 1-p.m polished area under the binocular microscope to make sure that all the 800-grit 

scratches along this 1- to 2-cm-wide strip have been removed and only the fine scratches produced by the 1-p.m diamond paste remain. These 1-p.m scratches can be easily identified since 

they are parallel to the length of the sample. 

6. Use another bolt or rod having a clean TEXMET substrate charged with 1/4-p.m diamond paste. 

Again exerting moderate pressure and maintaining flat contact with the coal-sample surface, 

polish perpendicular to the 1-p.m scratches. Polish for about 30 to 40 s. Wash with soap solution 

and distilled water, and dry the sample with compressed air. After it has been washed and dried, 

the surface should appear free of scratches or water or oil streaks. The sample is now ready for 

photographic documentation, observation, study, and microscopic image analysis. 

We have encountered very few problems with scratches and polishing defects when we have used this 

procedure. Perhaps applying the polishing pressure downward and limiting the strip to be polished to a 

width of 2 em or less are helpful. The entire in-place polishing process for a coal sample about 10 em long 

should take less than 5 min on the average. 

APPENDIX 3: CHECKLIST FOR BINOCULAR MEGASCOPIC DESCRIPTION 

I. Structural and textural characteristics and description: 

A. Layering or banding characteristics: 

Information pertaining to the mode of formation of the coal: autochthonous (accumulated essentially in place); hypautochthonous (all subaquatically formed lithotypes, such as cannel and boghead coals); allochthonous (transported, redeposited). 

1. Well banded or layered (autochthonous)-Recommend that bands 2 mm and thicker 

·be shown on the columnar section (fig. 2A). 

2. Nonbanded or not banded (hypautochthonous)-Example: Cannel and boghead 

coals; some mineral-rich, fine-grained, impure coals. 

3. Irregularly layered-Irregular, discontinuous, or lenticular texture suggesting accumulation after transport (allochthonous) (fig. 2B). Examples-For vi trite aggregates, describe thin (1-2 p.m), several centimeters long as 'ivitrite lenses"; 

"vitrite laminae" (0.05-1 mm), several centimeters long; or "irregular vitrite," 

wedge-shaped, a few millimeters to several centimeters long; and so forth. 

2

A product of Buehler, Ltd., Evanstcn, IL 60204. The use of tzade or brand names does not cmstitute endorsement of products by the U.S. Geological Survey. 

30 
B. Texture or grain size where appropriate: 

1. Coarse particulate texture, millimeter-sized particles, and so forth. 

2. Fine particulate texture, smooth and uniform, and so forth. 

C. Cleat and other fractures where appropriate; may be omitted if not significant or notable. 

II. Microlithotype, lithotype, and petrographic unit identification and description: 

A. Describe and characterize (V) (vitrite or vitrain), (E) (liptite, usually rare), (I) (inertite or 

fusite or fusain), (M) (mineral band), (S) (pyritic band or lenses), and (Xl), (X2), and other 

mixed lithologies. 

B. Demarcate lithologic bands or layers 2 mm thick or more on the columnar section at proper 

intervals. 

C. Note cyclicity of lithologic types if present. 

III. Demarcation of petrographic units based on: 

A. Abrupt changes in lithologic composition. 

B. Abrupt changes in textural or structural features. 

IV. By using a good binocular microscope and good, even illumination, it is possible, in some coals, to 

record observations such as: 

A. Association of exinites in different lithologic types: 

1. Microspores versus megaspores. 

2. Relative abundance of cutinite. 

B. Concentration and distribution of fusinitized rodlets. 

C. Abundance of minerals, clay, quartz, and sulfide. 

D. Abundance of inertinites. 

V. Bulk property description in conjunction with lithologic types: 

A. Color and luster, such as dark gray and bright, light gray and dull, and so forth. 

B. Bulk density-During or after the binocular examination, to determine additional characteristics of certain lithologic units described, select chips for bulk density test using 

''Certigrav'' density liquids. Be certain to select and remove chips that represent a single 

lithologic type and that do not include portions of overlapping units or adjacent 

partings. 

VI. Miscellaneous notes: 

Make note of anything that is unusual, such as the way that the coal breaks, liquid exuding, 

crosscutting veinlets filled with secondary minerals, reaction product with moisture or exposure to air, and so forth. 

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