Rock coring is the standard method for obtaining subsurface data concerning coals in the Southern Appalachian Coal Fields. This method, although the most costly, provides the most complete record of the materials found at any particular location. Unfortunately, much of this potentially valuable information is lost due to inadequate descriptions of the rock core recovered from the hole. In some cases, this is due to misidentification, but mostly it arises from the lack of uniform terminology. The objective of this book is to provide a standard base for core description which will aid in the recognition of different kinds of rocks and provide a uniform set of terms for describing them.

This book contains a set of color photographs of cores of the common rock types in the Southern Appalachian Coal Fields with some specimens moistened with water in order to show particular properties. Each specimen is given a name and a three digit number which convey characteristics of grain size, composition, color, structure and/or bedding. The photographs are grouped into major rock classes which are accompanied by a short text describing properties that are useful in differentiating rock types within the class. Also given are the keys for recognizing the rock types.

Rock names in this book are a combination of geologist's and driller's terms and should aid drillers and engineers in becoming familiar with standard descriptive geologic terminology. They should also reduce the number of words geologists require to portray rock characteristics. Moreover, because fewer words and terms are required, core logging is faster and more efficient, saving expensive field time and reducing the tedium of logging. Finally, such a system, using short, standard phrases or numbers, lends itself to computer techniques of data input, storage, and retrieval.

The geographic area in which this book is to be used is shown on Figure 1. The eastern and western boundaries are the approximate limits of coal bearing rocks in the Southern Appalachian region. The northern boundary is an arcuate east-west trending line located just south of Charleston, West Virginia where the older coal bearing rocks of the Southern Appalachian Coal Fields dip beneath the younger strata of the Pittsburgh Basin. The southern boundary is a northwest trending line 35 miles south of Birmingham, Alabama where coal bearing rocks dip beneath the poorly consolidated strata of the Gulf Coastal Plain. The region thus defined includes the major coal producing regions of southern West Virginia, eastern Kentucky, southwestern Virginia, and northern Alabama as well as areas with smaller estimated reserves in eastern Tennessee and northwestern Georgia.

Throughout most of this region, the kinds of rock overlying and underlying the major coal seams display remarkable uniformity and the samples shown in this book provide an adequate guide to their description. Along the northern boundary of the region, however, the more vividly colored red and green shales of the Pittsburgh Basin overlap the darker rocks of the Southern Appalachian Basins. The companion volume to this book–A Guide to Cored Rocks in the Pittsburgh Basin* –may be required to produce a complete core description. Along the southern boundary, the soft sands and clays of the Gulf Coastal Plain which overlie the coal bearing rocks are only rarely recovered as core and are thus not illustrated in this book.

*A Guide to Cored Rocks in the Pittsburgh Basin, J.C. Ferm and G.C. Smith, Department of Geology, University of Kentucky, Lexington, Kentucky, 1981, 109p.

Aside from the general notion that current methods of core description can be improved, standardized core descriptions have direct and immediate application to the problems of mine planning, mine development and coal exploration.

The cores logged by methods described in this book should alert engineers to rock types which can produce problems in slope and shaft construction. For example, certain kinds of sandstone and pebbly sandstone carry sufficient water to make pregrouting a necessity. Some very soft fireclays are well known for their tendency for caving and require special construction methods.

In planning underground mines, accurate core descriptions facilitate placement of projections in areas of best roof and floor or at least indicate areas of potential difficulty in ground control. For example, it is reasonably well established that some rocks (e.g. fireclays of considerable thickness) or certain kinds of contacts (e.g. sandstone in sharp contact with shale) can cause problems in roof control. Accurately described cores indicate the presence of these rocks in the roof of areas to be mined and such areas can be taken into consideration during preparation of the mine plan.

Some preliminary evidence indicates a general association of rock types shown in this book with precisely measured physical properties such as unconfined compressive strength. Hence, sophisticated sampling schemes for estimation of such physical parameters should take into account the type of rock upon which measurements are to be made.

Precise and accurate rock descriptions produced by the core book method can aid in establishing seam characteristics and seam continuity. If a seam tends to pinch out or is cut out by "faults" or "washouts", or if there is some tendency for splitting, observations such as those obtained by using this system are essential in defining areas where the coal is workable or defining distances between minable areas of the seam.

During exploration, shallower seams are often encountered in the course of drilling for a deep target seam. Precise logging will not only assist in predicting the exact position of the target seam, but it will also insure the availability of good records if shallower seams assume economic importance in the future.

Finally it should be noted that the geological concepts of depositional environments of coal seams are now being utilized in order to understand variations in coal quality, seam thickness and seam continuity as well as predicting roof and floor rock types. Precise and accurate core description is the first and essential step in applying these concepts.

A list of rock types occurring in the Southern Appalachian Coal Fields and the page number on which they are illustrated is shown on Table 5 at the end of this book. Examination of this table shows that coal and bone are not illustrated. The principle reason for this is that most core loggers are already experienced and knowledgeable in describing these rocks. Secondly, minable seams are generally removed from the core pile shortly after drilling and hence pass beyond the urview of the field observer.

Names that have been applied to rock types illustrated in this book are a combination of driller's and geologist's terms, but in every case, the driller's term is used where at all feasible. Where there is no driller's equivalent or the driller's terms are too confusing or obscure, the simplest geologic term is employed. Some geologists may object to this practice because it is somewhat imprecise in the context of conventional petrologic description. It should be recognized, however, that the most important factor in these descriptions is the photograph and its accompany number which comprise a basic tool of communication for geologists, engineers and drillers. If more detailed information is required, the rock types described here can be used as a base for more precise descriptions of grain size, mineral composition, physical strength and chemical characteristics.

Appended to each rock name is a code number. The use of numbers rather than written words is an efficient method for recording data. Moreover, it simplifies the question of terminology and permits rapid manipulation of the data by computer.

Equipment and Technique

Tools and techniques for the determination of rock types are relatively simple. Aside from the book itself (and a notebook or tape recorder for recording data), the principal tools are a small hammer for breaking the core and a pocket knife for scratching it. It is also necessary to have a nearby source of water for washing the core; (a large paint brush or white-wash brush is also helpful). A bright colored wax crayon or water-fast marking pen is useful for writing on any specimens that may be collected. Finally, it is highly desirable to have a small dropper bottle containing a 10% solution of hydrochloric acid, an item that can be obtained in most pharmacies.

The first step in describing a core is washing and aligning. The latter step is a matter of convenience because misaligned core creates difficulties in measurement. Washing or wetting is necessary mainly with some sandstones and conglomerates where grains or pebbles are obscured by cementation or overlapping between grains. Some of the rocks illustrated in the book are shown both wet and dry specifically to demonstrate the value of wetting the core.

In order to compare the core with the photograph in the book, it is not necessary to hold the book next to the core as the eye readily adjusts for distance; most observations can be made at distances of up to five feet. Some care may be necessary in comparing colors shown in this book with those found under field conditions. Samples appearing in the book were photographed against a neutral background and hence are the closest approximation to true color. Cores compared to the photographs under any other conditions may not match perfectly. Clothing, ground color, foliage, sky color and temperature will affect the color of the rock and the photograph. Consequently it may be difficult in some cases to match colors exactly. Such differences, however, are generally so small that they go unnoticed or are negligible in terms of identifying rock types.

Actual handling of the core is usually necessary only to distinguish different subtypes within major rock classes, especially in the finer grained rocks such as shales, sandy shales and fireclays. In these rocks, the degree of grittiness can be detected by touching or lightly rubbing the core with forefinger or thumb. Some geologists detect grittiness by rubbing a small bit of rock against their teeth. This is a sensitive technique but ultimately damaging to tooth enamel. Scratching the core with a knife blade or fingernail is sometimes used to detect grittiness or hardness and is especially important in distinguishing coals, bones and black shales. Dilute hydrochloric acid is essential in detecting the presence of calcium carbonate (lime).

Specific procedures for measurement of rock thickness vary widely. Drillers usually employ a combination of direct thickness measurement and known depth of the hole. Engineers and geologists generally measure thickness found in the core pile in combination with depths marked on the core by the driller or the results of a geophysical log.

Rock Identification

There are several techniques for using this book to identify rocks. One that is not recommended is simply leafing through the pictures in hopes of finding an appropriate example. Such a procedure wastes time and can easily lead to erroneous identification. One procedure that has worked very well in past trials consists of placing the core in question in one of the following major rock groups and then determining the specific rock type within that group:

Sandstones, Pebbly Sandstones, and Conglomerates
SandyShales and Sandy Fireclays
Shales and Fireclays
Ironstones, Limestones and Flint Clays
Deformed Rocks

Table 1, shown below, gives specific instructions for identifying core with respect to major rock groups and, within each group, makes reference to color coded sections of the book. Within each color coded section are instructions for identifying rock types within groups.

Throughout the book, where reference is made to a photograph, the page number is given and the position of the photograph on the right or left side of the page is indicated by the letters "R" for right and "L" for left. For example, a reference to the right side of page 18 is given 18R.

Where there is only one specimen on a page or reference is made to both specimens on a page, only the page number is given.