Coal Glossary

A
accessed--Coal deposits that have been prepared for mining by construction of portals, shafts, slopes, drifts, and haulage ways; by removal of overburden; or by partial mining (see also virgin coal).
accessibility--In reference to coal resources (core meaning), the absence of land use restrictions and the assumption that ownership or leaseholds will be obtainable for mining (see also environmental restrictions, industrial restrictions). Many technological restrictions were traditionally applied as demonstrated reserve base criteria, but (extended meaning) with the advent of available resource studies, specific technologic restrictions may be incorporated in accessibility factors (see also restricted resources).
accessibility factor--The estimated regional ratio of accessible reserve base to the demonstrated reserve base or of accessible resources to identified resources.
accessible reserve base--The portion of the demonstrated reserve base estimated by EIA to be accessible, determined by application of one or more accessibility factors within an area. An accessible reserve base may be referred to as accessible resources because it is a subset of accessible resources and is usually part of a single resource study.
accessible resources--The portion of identified resources estimated to be accessible, determined by application of one or more accessibility factors within an area.
as-received condition or as-received basis--Represents an analysis of a sample as received at a laboratory.
availability--In reference to coal resources, the absence of land-use or environmental restrictions and technological restrictions.
available reserves-- the remaining reserves after deducting the leased reserves from proven reserves. In EIA coal supply modeling, the difference between estimated recoverable reserves and recoverable reserves at active mines; in modeling context, these reserves are considered not presently obligated for existing mines and, therefore, would be available to supply new mines in the future.
available resources--In U.S. Geological Survey studies, the quantity of remaining identified resources available for development and potential extraction at the time of determination after adjusting for geologic considerations, land-use restrictions, and/or technological restrictions (see also accessible reserve base).
B
bed, coalbed--All the coal and partings lying between a roof and floor.

bench--A subdivision and (or) layer of a coal bed separated from other layers by partings of non-coal rock.
bench sample--a face or channel sample taken of just that contiguous portion of a coalbed that is considered practical to mine, also known as a "bench;" For example, bench samples may be taken of minable coal where impure coal that makes up part of the geologic coalbed is likely to be left in the mine, or where thick partings split the coal into two or more distinct minable seams, or where extremely thick coalbeds cannot be recovered by normal mining equipment, so that the coal is mined in multiple passes, or benches, usually defined along natural bedding planes.
Brown coal (Lignite)-- also known as "wood coal", is brownish-black in color and considered the lowest rank of coal. The moisture content of brown coal is high, between 30% and 45%, and volatile matter above 36%. It is low in calorific value, easy to weathering and crack. It could also burn spontaneously as been oxidized easily. Therefore, brown coal is unsuitable for long-distance transportation. But, it could be mined easily because of shallow burying depth, hence low in development and utilization costs.
C
clean coal yield--In EIA models, the portion of reserves that will be salable coal after preparation, if any is done (see salable coal).
Coal chemical-- An industry that converts coal into gas, liquid and solid products or semi-products, as well as chemical and energy products after further processing. It includes coke making, calcium carbide chemical, coal gasification, etc. Due to reducing oil resources worldwide, the future of coal chemical industry is wide and promising.

coal preparation/washing--The treatment of coal to reject waste. In its broadest sense, preparation is any processing of mined coal to prepare it for market, including crushing and screening or sieving the coal to reach a uniform size, which normally results in removal of some non-coal material. The term coal preparation most commonly refers to processing, including crushing and screening, passing the material through one or more processes to remove impurities, sizing the product, and loading for shipment. Many of the processes separate rock, clay, and other minerals from coal in a liquid medium; hence the term washing is widely used. In some cases coal passes through a drying step before loading.

coal-producing region--An area that collectively encompasses a group of geographically contiguous or logically associated States or areas that currently or historically mine and market coal.

coal sampling--The collection and proper storage and handling of a relatively small quantity of coal for laboratory analysis. Sampling may be done for a wide range of purposes, such as: coal resource exploration and assessment, characterization of the reserves or production of a mine, to characterize the results of coal cleaning processes, to monitor coal shipments or receipts for adherence to coal quality contract specifications, or to subject a coal to specific combustion or reactivity tests related to the customer's intended use. During pre-development phases, such as exploration and resource assessment, sampling typically is from natural outcrops, test pits, old or existing mines in the region, drill cuttings, or drilled cores. Characterization of a mine's reserves or production may use sample collection in the mine, representative cuts from coal conveyors or from handling and loading equipment, or directly from stockpiles or shipments (coal rail cars or barges). Contract specifications rely on sampling from the production flow at the mining or coal handling facility or at the loadout, or from the incoming shipments at the receiver's facility. In all cases, the value of a sample taken depends on its being representative of the coal under consideration, which in turn requires that appropriate sampling procedures be carefully followed.

For coal resource and estimated reserve characterization, appropriate types of samples include:
face channel or channel sample--a sample taken at the exposed coal in a mine by cutting away any loose or weathered coal then collecting on a clean surface a sample of the coal seam by chopping out a channel of uniform width and depth; a face channel or face sample is taken at or near the working face, the most freshly exposed coal where actual removal and loading of mined coal is taking place. Any partings greater than 3/8 inch and/or mineral concretions greater than ?inch thick and 2 inches in maximum diameter are normally discarded from a channel sample so as better to represent coal that has been mined, crushed, and screened to remove at least gross non-coal materials.

column sample--a channel or drill core sample taken to represent the entire geologic coalbed; it includes all partings and impurities that may exist in the coalbed.

composite sample--a recombined coalbed sample produced by averaging together thickness-weighted coal analyses from partial samples of the coalbed, such as from one or more bench samples, from one or more mine exposures or outcrops where the entire bed could not be accessed in one sample, or from multiple drill cores that were required to retrieve all local sections of a coal seam.

coal supply region--An area in which the EIA coal reserves data are aggregated and allocated to a set of uniform, typical criteria for purposes of modeling. The criteria of a coal supply region may include coal heat and sulfur content or other quality parameters, coal rank, geographic continuity, traditional mining regions, State or county boundaries, transportation corridors and barriers, and marketing factors. Coal supply regions may vary for different modeling criteria; they may include the coal reserves of an entire State or a contiguous group of States; some major producing States may be split into more than one region.

coal zone--A series of laterally extensive and (or) lenticular coal beds and associated strata that arbitrarily can be viewed as a unit. Generally, the coal beds in a coal zone are assigned to the same geologic member or formation.

coalbed--All the coal and partings lying between a roof and floor.
Coalfield-- large area of coal-bearing zones formed by carbonaceous materials in the development of geological history.

committed reserves--In EIA coal supply modeling, synonymous with recoverable reserves at active mines; in modeling context, these reserves are considered obligated for existing mines and, therefore, not part of the reserves that would be available to supply new mines in the future.
compliance coal--A coal or a blend of coals that meets sulfur dioxide emission standards for air quality without the need for flue gas desulfurization.
cumulative depletion--The sum in tons of coal extracted and lost in mining to a stated date for a specified area or a specified coal bed.
D
demonstrated reserve base (DRB)--A collective term for the sum of coal in both measured and indicated resource categories of reliability; the DRB represents 100 percent of coal in place as of a certain date. Includes beds of bituminous coal and anthracite 28 inches or more thick and beds of subbituminous coal 60 inches or more thick that can be surface mined. Includes also thinner and/or deeper beds that presently are being mined or for which there is evidence that they could be mined commercially at this time. Represents that portion of the identified resources of coal from which reserves are calculated.

demonstrated resources--Same qualifications as identified resources, but includes measured and indicated degrees of geologic assurance and excludes the inferred.

depleted resources--Resources that have been mined; includes coal recovered, coal lost in mining, and coal rendered subeconomic as a result of mining the recovered coal. See cumulative depletion.
depletion--The subtraction of both the tonnage produced and the tonnage lost in mining from the demonstrated reserve base and identified resources to determine the remaining tonnage as of a certain time.
depletion factor--The multiplier of the tonnage produced that takes into account both the tonnage recovered and the tonnage lost due to mining. The depletion factor is the reciprocal of the recovery factor in relation to a given quantity of production.
Designed production capacity--the actual maximum production capacity under the premise of safety and with the existing equipments, technologies and workers in an enterprise.
dry, mineral-matter-free basis--A type of calculated analytical value of a coal sample expressed as if the total moisture and mineral matter had been removed. Mineral matter free is not the same as ash free.
E
economic--Term that implies that profitable extraction or production under realistic investment assumptions has been established, analytically demonstrated, or assumed with reasonable certainty.
environmental restrictions--Land-use or subsurface restrictions that constrain, postpone, or prohibit mining in order to protect environmental resources of an area; for example, surface- or groundwater quality, air quality affected by mining, or plants or animals or their habitats.
estimate--A determination as to the amount or tonnage of coal in an area. The term estimate indicates that the quantities of resources are known imprecisely. An estimate differs from an assessment, which is an analysis of all data concerning an area's coal resources and reserves with the objective of reaching a judgment about the geologic nature and economic potential of the coal resources and reserves of the area.
estimated recoverable reserves--See recoverable reserves.
F
floor--The upper surface of the stratum underlying a coal seam. In coals that were formed in persistent swamp environments, the floor is typically a bed of clay, known as "underclay," representing the soil in which the trees or other coal-forming swamp vegetation was rooted.
G
geologic assurance--State of sureness, confidence, or certainty of the existence of a quantity of resources based on the distance from points where coal is measured or sampled and on the abundance and quality of geologic data as related to thickness of overburden, rank, quality, thickness of coal, areal extent, geologic history, structure, and correlations of coal beds and enclosing rocks. The degree of assurance increases as the nearness to points of control, abundance, and quality of geologic data increases.
geologic considerations--Conditions in the coal deposit or in the rocks in which it occurs that may complicate or preclude mining. Geologic considerations are evaluated in the context of the current state of technology and regulations, so the impact on mining may change with time.
grade (of coal)--See quality.
H
hypothetical resources--Undiscovered coal resources in beds that may reasonably be expected to exist in known mining districts under known geologic conditions. In general, hypothetical resources are in broad areas of coalfields where points of observation are absent and evidence is from distant outcrops, drill holes, or wells. Exploration that confirms their existence and better defines their quantity and quality would permit their reclassification as identified resources. Quantitative estimates are based on a broad knowledge of the geologic character of coalbed or region. Measurements of coal thickness are more than 6 miles apart. The assumption of continuity of coalbed is supported only by geologic evidence.
I
identified resources--Specific bodies of coal whose location, rank, quality, and quantity are known from geologic evidence supported by engineering measurements. Included are beds of bituminous coal and anthracite 14 inches or more thick and beds of subbituminous coal and lignite 30 inches or more thick that occur at depths to 6,000 feet and whose existence and quantity have been delineated within specified degrees of geologic assurance as measured, indicated, or inferred.
indicated resources--Coal for which estimates of the rank, quality, and quantity have been computed partly from sample analyses and measurements and partly from reasonable geologic projections. Indicated resources are computed partly from specified measurements and partly from projection of visible data for a reasonable distance on the basis of geologic evidence. The points of observation are 0.5 to 1.5 miles apart. Indicated coal is projected to extend as a 0.5-mile-wide belt that lies more than 0.25 miles from the outcrop or points of observation or measurement.
industrial restrictions--Land-use restrictions that constrain, postpone, or prohibit mining in order to meet other industrial needs or goals; for example, resources not mined due to safety concerns or due to industrial or societal priorities, such as to preserve oil or gas wells that penetrate the coal reserves; to protect surface features such as pipelines, power lines, or company facilities; or to preserve public or private assets, such as highways, railroads, parks, or buildings.
inferred reserve base--the resources in the inferred reliability category that meet the same criteria of bed thickness and depth from surface as the demonstrated reserve base.
inferred resources--Coal in unexplored extensions of demonstrated resources for which estimates of the quality and size are based on geologic evidence and projection. Quantitative estimates are based largely on broad knowledge of the geologic character of the bed or region and where few measurements of bed thickness are available. The estimates are based primarily on an assumed continuation from demonstrated coal for which there is geologic evidence. The points of observation are 1.5 to 6 miles apart. Inferred coal is projected to extend as a 2.25-mile-wide belt that lies more than 0.75 miles from the outcrop or points of observation or measurement.
--A line on a map drawn through points of equal thickness of a designated unit (such as a coal bed).
L
land-use restrictions--Constraints placed upon mining by societal policies to protect surface features or entities that could be affected by mining. Because laws and regulations may be modified or repealed, the restrictions, including industrial and environmental restrictions, are subject to change.
M
marginal reserves--Borders on being economic. See economic.
measured resources--Coal for which estimates of the rank, quality, and quantity have been computed, within a high degree of geologic assurance, from sample analyses and measurements from closely spaced and geologically well known sample sites. Measured resources are computed from dimensions revealed in outcrops, trenches, mine workings, and drill holes. The points of observation and measurement are so closely spaced and the thickness and extent of coals are so well defined that (for older estimates) the tonnage was judged to be accurate within 20 percent of true tonnage (statistical measures of error are no longer considered reliable for most measured resources). Although the spacing of the points of observation necessary to demonstrate continuity of the coal differs from region to region according to the character of the coalbeds, the points of observation are not greater than 0.5 mile apart. Measured coal is projected to extend as a 0.25-mile-wide belt from the outcrop or points of observation or measurement.
minable--Capable of being mined under current mining technology and environmental and legal restrictions, rules, and regulations.
O
original (resources/reserves)--The amount of coal in the ground before any production.
overburden--Any material, consolidated or unconsolidated, that lies between a coal deposit and the surface. Overburden is reported in feet and (or) meters and used to classify the depth to an underlying coal bed.
P
preparation plant--Broadly speaking, any facility where coal is prepared for market; usual accepted meaning is a rather elaborate collection of facilities where coal is separated from its impurities, washed and sized, and loaded for shipment. Also known as a wash plant or coal washer.
Q
quality or grade--An informal classification of coal relating to its suitability for use for a particular purpose. Refers to individual measurements such as heat value, fixed carbon, moisture, ash, sulfur, phosphorus, major, minor, and trace elements, coking properties, petrologic properties, and particular organic constituents. The individual quality elements may be aggregated in various ways to classify coal for such special purposes as metallurgical, gas, petrochemical, and blending usages.
R
rank--The classification of coal relative to other coals, according to their degree of metamorphism, or progressive alteration, in the natural series from lignite to anthracite (Standard Classification of Coal by Rank, 1992, American Society for Testing and Materials, ASTM Designation D-388-91a).
recoverability--In reference to accessible coal resources, the condition of being physically, technologically, and economically minable. Recovery rates and recovery factors may be determined or estimated for coal resources without certain knowledge of their economic minability; therefore, the availability of recovery rates or factors does not predict recoverability.
recoverable coal--Coal that is, or can be, extracted from a coal bed during mining.
recoverable reserves, estimated recoverable reserves--Reserve estimates (broad meaning) based on a demonstrated reserve base adjusted for assumed accessibility factors and recovery factors. The term is used by EIA to distinguish estimated recoverable reserves, which are derived without specific economic feasibility criteria by factoring (downward) from a demonstrated reserve base for one or more study areas or regions, from recoverable reserves at active mines, which are aggregated (upward) from reserve estimates reported by currently active, economically viable mines on Form EIA-7A.
recoverable reserves at active mines--The amount of in situ coal that can be recovered by mining existing reserves at mines reporting on Form EIA-7A (see committed reserves).
recovery factor--The percentage of total tons of coal estimated to be recoverable from a given area in relation to the total tonnage estimated to be in the demonstrated reserve base. For the purpose of calculating depletion factors only, the estimated recovery factors for the demonstrated reserve base generally are 50 percent for underground mining methods and 80 percent for surface mining methods. More precise recovery factors can be computed by determining the total coal in place and the total coal recoverable in any specific locale.
recovery percentage/rate--The ratio of coal extracted from a bed as compared to the total quantity of coal originally in the bed.
remaining (resources/reserves)--The amount of coal in the ground after some mining, excluding coal in the ground spoiled or left in place for which later recovery is not feasible.
regional reserves, regional reserve estimates--Same as reserves; alternative wording is used by EIA to distinguish regional reserves, which are derived by factoring (downward) from a demonstrated reserve base for one or more study areas or regions, from reserves at active mines, which are aggregated (upward) from reserve estimates reported by individual mines on Form EIA-7A.
remaining (resources/reserves)--The amount of coal in the ground after some mining, excluding coal in the ground spoiled or left in place for which later recovery is not feasible.
reserve(s)--Root meaning: The amount of in-situ coal in a defined area that can be recovered by mining at a sustainable profit at the time of determination. Broad meaning: That portion of the demonstrated reserve base that is estimated to be recoverable at the time of determination. The reserve is derived by applying a recovery factor to that component of the identified resources of coal designated as the demonstrated reserve base.
reserves at active mines--The amount of in situ coal that can be recovered by mining existing reserves at mines reporting on Form EIA-7A (see committed reserves).
resources--Naturally occurring concentrations or deposits of coal in the Earth's crust, in such forms and amounts that economic extraction is currently or potentially feasible.
resource reserves--refers to the proven geological reserves.

restricted coal resources--In U.S. Geological Survey studies, the quantity of remaining resources that is not available for development at the time of determination because of geologic considerations, land-use restrictions, and/or technological restrictions.
restricted resources--Those parts of any resource category that are restricted or prohibited from extraction by laws or regulations. Also, coal or a portion of the coal in categorically minable depths or thicknesses that is not economic at the time of determination.
roof--The rock immediately above a coal seam. The roof is commonly a shale, often carbonaceous and softer than rocks higher up in the roof strata.

run-of-mine--The raw coal recovered from a mine, prior to any treatment.
S
salable coal--The shippable product of a coal mine or preparation plant. Depending on customer specifications, salable coal may be run-of-mine, crushed-and-screened (sized) coal, or the clean coal yield from a preparation plant.
sample--A representative fraction of a coal bed collected by approved methods, guarded against contamination or adulteration, and analyzed to determine the nature; chemical, mineralogic, and (or) petrographic composition; percentage or parts-per-million content of specified constituents; heat value; and possibly the reactivity of the coal or its constituents.
seam--A bed of coal lying between a roof and floor. Equivalent term to bed, commonly used by industry.
speculative resources--Undiscovered coal in beds that may occur either in known types of deposits in a favorable geologic setting where no discoveries have been made, or in deposits that remain to be recognized. Exploration that confirms their existence and better defines their quantity and quality would permit their reclassification as identified resources.
strip or stripping ratio--The amount of overburden that must be removed to gain access to a unit amount of coal.
Discussion: A stripping ratio may be expressed as (1) thickness of overburden to thickness of coal, (2) volume of overburden to volume coal, (3) weight of overburden to weight of coal, or (4) cubic yards of overburden to tons of coal. A stripping ratio commonly is used to express the maximum thickness, volume, or weight of overburden that can be profitably removed to obtain a unit amount of coal.
strip or surface mining--The extraction of coal by using surface mining methods such as area strip mining, contour strip mining, or open-pit mining. The overburden covering the coal is removed and the coal extracted using power shovels, front-end loaders, or similar heavy equipment.
T
technological restrictions--Constraints related to economics and safety placed upon mining by contemporary technology or prescribed by law; the restrictions may change with advances in science or modifications in the law. For purposes of assessing impacts on minability, geologic considerations are included as technological restrictions. A secondary basis for accessibility is the technological restrictions that may affect economic minability of specific coal resources in a locality at the time of the evaluation. Technological restrictions include constraints on the economic or safe mining of the coal with contemporary technologies, which constraints are related to the nature of the coalbeds or local geology; for example, specific coalbed thickness or overburden characteristics known to deter economic mining of coal meeting broad regional DRB criteria, localized geologic structural problems, or unsafe or illegal proximity to another mine.

U
underground mining--The extraction of coal or its products from between enclosing rock strata by underground mining methods, such as room and pillar, longwall, and shortwall, or through in-situ gasification.
undiscovered resources--Unspecified bodies of coal surmised to exist on the basis of broad geologic knowledge and theory. Undiscovered resources include beds of bituminous coal and anthracite 14 inches or more thick and beds of subbituminous coal and lignite 30 inches or more thick that are presumed to occur in unmapped and unexplored areas to depths of 6,000 feet. The speculative and hypothetical resource categories comprise undiscovered resources.

V
virgin coal--Coal that has not been accessed by mining. See accessed.