ASTM D2799-23

Standard Test Method for Microscopical Determination of the Maceral Composition of Coal

SIGNIFICANCE AND USE
5.1 The volume fraction of physical components of coal is used as an aid in coal seam correlation and in the characterization of coals for their use in carbonization, gasification, liquefaction, and combustion processes.  
5.2 This test method is for use in scientific and industrial research, not compliance or referee tests.
SCOPE
1.1 This test method covers the equipment and techniques used for determining the physical composition of a coal sample in terms of volume fraction of the organic components and of mineral matter, if desired by systematic manual point count.  
1.2 The term weight is temporarily used in this test method because of established trade usage. The word is used to mean both force and mass and care must be taken to determine which is meant in each case (the SI unit for force is newton and for mass, kilogram).  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Jan-2023
• ICS: 73.040 - Coals
• Technical Committee: D05 - Coal and Coke
• Drafting Committee: D05.28 - Petrographic Analysis of Coal and Coke

Relations

• Refers: ASTM D121-15(2024) - Standard Terminology of Coal and Coke
• Effective Date: 01-Mar-2024
• Refers: ASTM D2798-11a(2019) - Standard Test Method for Microscopical Determination of the Vitrinite Reflectance of Coal
• Effective Date: 01-Nov-2019
• Refers: ASTM E562-19e1 - Standard Test Method for Determining Volume Fraction by Systematic Manual Point Count
• Effective Date: 15-Aug-2019
• Refers: ASTM D388-19 - Standard Classification of Coals by Rank
• Effective Date: 01-Jun-2019
• Refers: ASTM D388-18a - Standard Classification of Coals by Rank
• Effective Date: 01-Nov-2018
• Refers: ASTM D4239-18 - Standard Test Method for Sulfur in the Analysis Sample of Coal and Coke Using High-Temperature Tube Furnace Combustion
• Effective Date: 01-Sep-2018
• Refers: ASTM D388-18 - Standard Classification of Coals by Rank
• Effective Date: 01-Feb-2018
• Refers: ASTM D388-17a - Standard Classification of Coals by Rank
• Effective Date: 01-Nov-2017
• Refers: ASTM D388-17 - Standard Classification of Coals by Rank
• Effective Date: 01-Jul-2017
• Refers: ASTM D4239-17 - Standard Test Method for Sulfur in the Analysis Sample of Coal and Coke Using High-Temperature Tube Furnace Combustion
• Effective Date: 15-May-2017
• Refers: ASTM D121-15 - Standard Terminology of Coal and Coke
• Effective Date: 01-Sep-2015
• Refers: ASTM D388-15 - Standard Classification of Coals by Rank
• Effective Date: 15-May-2015
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM D4239-14 - Standard Test Method for Sulfur in the Analysis Sample of Coal and Coke Using High-Temperature Tube Furnace Combustion
• Effective Date: 01-Mar-2014
• Refers: ASTM D4239-14e1 - Standard Test Method for Sulfur in the Analysis Sample of Coal and Coke Using High-Temperature Tube Furnace Combustion
• Effective Date: 01-Mar-2014

Overview

ASTM D2799-23: Standard Test Method for Microscopical Determination of the Maceral Composition of Coal is an essential standard developed by ASTM International. This method details the recommended apparatus, procedures, and criteria for the microscopical analysis of coal to determine its maceral composition and, if desired, its mineral matter. Accurate maceral analysis is critical in coal characterization, aiding in understanding coal seam correlation and coal’s suitability for key industrial processes, including carbonization, gasification, liquefaction, and combustion.

This test method is primarily intended for use in scientific and industrial research rather than for compliance or referee testing. It provides a framework for petrographic analysis of coal by systematic manual point count using a reflected light microscope, following internationally recognized standards for precision and reproducibility.

Key Topics

• Maceral Identification: The method defines the classification of coal macerals into three major groups based on optical properties observed under a microscope:

  • Vitrinite: Intermediate reflectance, primarily derived from plant tissues.
  • Liptinite: Lower reflectance, known for its fluorescence under blue to ultraviolet light, derived from plant cuticles, resins, and spores.
  • Inertinite: High reflectance, includes macerals like fusinite, semifusinite, and micrinite, often derived from highly oxidized or degraded plant matter.

• Sample Preparation: Analysis requires coal samples prepared as polished briquettes, following standard specimen preparation practices.

• Microscopical Techniques: Uses a microscope equipped for reflected light observation, with systematic manual point counting ensuring statistically robust quantification of maceral and mineral matter fractions.

• Volume Fraction Determination: Maceral and mineral matter components are determined as volume fractions, which support correlating coal structure with performance in various industrial processes.

• Precision and Reproducibility: The standard specifies guidelines to report results, including best practices to improve repeatability and reproducibility across laboratories.

Applications

• Coal Characterization: The method supports detailed coal analysis, informing decisions on coal quality and usage in industries such as power generation, metallurgy, and chemical processing.

• Process Optimization: By understanding the maceral composition, users can predict coal behavior during carbonization, gasification, and combustion, optimizing process efficiency and product yields.

• Coal Seam Correlation: Petrographic data improves seam correlation and geological modeling by linking coal's physical attributes with its depositional history.

• Scientific Research: Enables researchers to study the origin, transformation, and distribution of organic components in coals of varying rank and from different geological locations.

• Quality Control: While not intended for compliance testing, the standard is a valuable tool for laboratories engaged in routine petrographic analyses and inter-laboratory proficiency programs.

Related Standards

• ASTM D121: Terminology of Coal and Coke - Provides definitions of terms used in coal analysis.
• ASTM D388: Classification of Coals by Rank - Describes the ranking system for coals based on properties like reflectance and fixed carbon.
• ASTM D2797: Practice for Preparing Coal Samples for Microscopical Analysis by Reflected Light - Guidance on specimen preparation prior to petrographic analysis.
• ASTM D2798: Test Method for Microscopical Determination of the Vitrinite Reflectance of Coal - Related test for measuring a key optical property.
• ASTM D3174: Test Method for Ash in the Analysis Sample of Coal and Coke from Coal - Used for determining coal ash content.
• ASTM D4239: Test Method for Sulfur in the Analysis Sample of Coal and Coke Using High-Temperature Tube Furnace Combustion - For sulfur quantification.
• ASTM E562: Test Method for Determining Volume Fraction by Systematic Manual Point Count.
• ASTM E691: Practice for Conducting Interlaboratory Studies to Determine the Precision of a Test Method.

Keywords: coal macerals, petrographic analysis, vitrinite, liptinite, inertinite, mineral matter, ASTM D2799, coal characterization, manual point count, coal microscopy, coal industry standards.

By following ASTM D2799-23, laboratories and researchers can ensure consistency and reliability in coal maceral analysis, supporting informed decisions in energy production and coal utilization industries.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D2799 − 23
Standard Test Method for
Microscopical Determination of the Maceral Composition of
Coal
This standard is issued under the fixed designation D2799; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D4239 Test Method for Sulfur in the Analysis Sample of
Coal and Coke Using High-Temperature Tube Furnace
1.1 This test method covers the equipment and techniques
Combustion
used for determining the physical composition of a coal sample
E177 Practice for Use of the Terms Precision and Bias in
in terms of volume fraction of the organic components and of
ASTM Test Methods
mineral matter, if desired by systematic manual point count.
E562 Test Method for Determining Volume Fraction by
1.2 The term weight is temporarily used in this test method
Systematic Manual Point Count
because of established trade usage. The word is used to mean
E691 Practice for Conducting an Interlaboratory Study to
both force and mass and care must be taken to determine which
Determine the Precision of a Test Method
is meant in each case (the SI unit for force is newton and for
3. Terminology
mass, kilogram).
3.1 Definitions—For definitions of terms, refer to Terminol-
1.3 This standard does not purport to address all of the
ogy D121.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.2 Classification—The classification of the microscopic
priate safety, health, and environmental practices and deter-
constituents into groups of similar properties in a given coal is
mine the applicability of regulatory limitations prior to use.
as follows:
1.4 This international standard was developed in accor-
Maceral Group Maceral
dance with internationally recognized principles on standard-
Vitrinite —
Liptinite alginite
ization established in the Decision on Principles for the
cutinite
Development of International Standards, Guides and Recom-
resinite
mendations issued by the World Trade Organization Technical
sporinite
Inertinite fusinite
Barriers to Trade (TBT) Committee.
inertodetrinite
macrinite
2. Referenced Documents
micrinite
2 funginite
2.1 ASTM Standards:
secretinite
D121 Terminology of Coal and Coke
semifusinite
D388 Classification of Coals by Rank
D2797 Practice for Preparing Coal Samples for Microscopi-
3.3 Many laboratories associated with the coke-making
cal Analysis by Reflected Light
industry use the following simplified classification for petro-
D2798 Test Method for Microscopical Determination of the
graphic analysis of bituminous coal:
Vitrinite Reflectance of Coal
Maceral Group Maceral
D3174 Test Method for Ash in the Analysis Sample of Coal Vitrinite vitrinite
Liptinite liptinite (other than resinite)
and Coke from Coal
resinite
Inertinite semifusinite
micrinite
This test method is under the jurisdiction of ASTM Committee D05 on Coal fusinite
and Coke and is the direct responsibility of Subcommittee D05.28 on Petrographic mineral matter
Analysis of Coal and Coke.
Other organizations use different classifications.
Current edition approved Feb. 1, 2023. Published February 2023. Originally
3.4 Definitions of Terms Specific to This Standard:
approved in 1969. Last previous edition approved in 2021 as D2799 – 21. DOI:
10.1520/D2799-23.
3.4.1 alginite, n—a liptinite maceral that is generally spheri-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
cal or ovoid, frequently having a crenulated border and
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
somewhat irregular reflectance and sometimes occurring in
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. clusters reflecting an origin from Botryococcus algae.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2799 − 23
3.4.1.1 Discussion—Alginite often occurs as degraded frag- processes and may contain up to several weight percent of
ments derived from colonial or unicellular bodies. inorganic elements in microscopically indistinguishable form.
3.4.10 maceral classification, n—The systematic division of
3.4.2 cutinite, n—a liptinite maceral in the form of a sheet
the organic substances (macerals) in coal based on their
reflecting its origin from leaf- or twig-covering plant cuticle,
appearance in the optical microscopic.
frequently exhibiting reticulation in planar section and a
3.4.10.1 Discussion—Although macerals may be identified
serrated edge in cross section.
in translucent, thin sections using criteria not defined herein,
3.4.3 exinite, n—Deprecated term. Use preferred term lip-
this test method deals only with identification and classification
tinite; sometimes has also been used as a synonym for
based on microscopic appearance on polished surfaces accord-
sporinite.
ing to Practice D2797. Three major maceral groups are
3.4.4 funginite, n—an inertinite maceral occurring as round
recognized on the basis of relative reflectance in white light,
or ovoid bodies, frequently containing voids, reflecting an
specifically: vitrinite—moderately reflecting (intermediate
origin from fungal sclerotia; also occurs (especially in lower
gray), liptinite—poorly reflecting (black to dark gray), and
rank coals) as interlaced, stringy materials derived from fungal
inertinite—highly reflecting (light gray to white). Each group
hyphae.
can be subdivided on the basis of other microscopically
distinctive features such as: reflectance contrasts (relative
3.4.5 fusinite, n—an inertinite maceral distinguished princi-
shades of gray); morphology, that is, shape and size (morpho-
pally by the preservation of some feature(s) of the plant cell
logic distinctions in definitions contained herein are idealized
wall structure, and with a particle size greater than 50 μm
because morphologic appearance depends on the initial form of
except when it occurs as a fragment within the binder matrix;
the source material, its state of preservation, including
see also semifusinite.
granulation, and on the orientation of the cross section pre-
3.4.6 inertinite, n—macerals that exhibit higher reflectance
sented on the polished preparation); spatial association with
than other organic substances in the coal.
other substances; fluorescence properties (color, intensity) in
3.4.6.1 Discussion—In any coal ranked lower than
blue to ultraviolet light; relief; color tinges; internal reflections;
anthracitic, inertinite reflectance commonly spans the range
and anisotropic properties.
from only slightly higher than associated vitrinite to very high
Microscopic criteria provide classification capability with-
reflectance (often as high as R max ≥ 6 %). In anthracitic rank
out any implication of absolute chemical composition or
o
coals, inertinite reflectance may be lower than that of vitrinite,
physical behavior, although some properties relative to other
and is then recognized by its morphology and form of
macerals in the same coal can be inferred broadly. Substances
anisotropy. Highly reflecting inertinite commonly exhibits
classified as the same maceral by microscopic criteria can
relief on polished surface. Its name derives from the fact that
differ chemically, physically, and characteristically in coals of
most varieties behave inertly in the thermoplastic deformation
different ranks. Some properties can be estimated by the
during the coking process (except in its lowest reflecting
measurement of reflectance (Test Method D2798).
manifestation). The volatile matter yield of inertinite is lower
See 3.3 for the classification used by most practitioners of
than that of other macerals in the same coal.
this test method.
3.4.11 macrinite, n—an inertinite maceral, generally
3.4.7 inertodetrinite, n—an inertinite maceral occurring as
individual, angular, clastic fragments incorporated within the nonangular, exhibiting no relict plant cell wall structure and
larger than 10 μm.
matrix of other macerals (commonly vitrinite) or minerals, and
in the size range from 2 μm to 50 μm.
3.4.12 micrinite, n—an inertinite maceral, generally
nonangular, exhibiting no relict plant cell wall structure,
3.4.8 liptinite, n—macerals that exhibit lower reflectance
smaller than 10 μm and most commonly occurring as particles
than other organic substances in a coal, appearing black to dark
around 1 μm to 5 μm diameter.
gray and that fluoresce under blue to ultraviolet light in coals
ranked high volatile bituminous and lower.
3.4.13 mineral matter, n—in coal, historically considered to
3.4.8.1 Discussion—The fluorescence of liptinite distin- be the non-organic fraction composed of physically discrete
particles of minerals, such as clays, quartz, pyrite, etc., and all
guishes fine-grained liptinite from similar sized, low
reflectance, nonfluorescing clay minerals. Liptinite is derived elements other than, carbon, hydrogen, oxygen, nitrogen, and
sulfur in the organic fraction.
principally from lipid substances forming skins (exines) and
resinous secretions or exudates of plants. Liptinite is sub-
3.4.14 resinite, n—a liptinite maceral occurring as rounded,
classified on the basis of morphology inherited from plant
ovoid, or rod-like bodies assuming the shape of an enclosing
structure. In coals in which vitrinite reflectance exceeds about
cell lumen or as irregular shapes filling cracks in the coal.
1.4 %, liptinite can be indistinguishable from vitrinite. Liptinite
3.4.15 secretinite, n—an inertinite maceral occurring as
has the highest volatile matter yield of the macerals in a coal.
round, ovoid, or oblong bodies, without obvious plant
3.4.9 maceral, n—an organic substance in coal that is
structure, vesicled to non-vesicled, sometimes containing char-
distinguished and classified (see maceral classification) on the
acteristic fractures, slits, or a notch.
basis of its optical microscopic properties.
3.4.15.1 Discussion—Secretinite is considered to be derived
3.4.9.1 Discussion—Macerals originate from plant tissues, by the oxidation of plant resin secretions or humic gels.
secretions, and exudates that have been altered by geological Vesicular and non-vesicular secretinite was formerly included
D2799 − 23
in sclerotinite of fungal origin. Secretinite is a common components are determined on a surface section of a sample.
maceral in medium- and high-rank Permian and Carboniferous However, the area and volume proportions are the same when
coals. the components are randomly distributed throughout the
sample.
3.4.16 semifusinite, n—an inertinite maceral with morphol-
4.1.1 Color photomicrographs of the maceral components
ogy like fusinite sometimes with less distinct evidence of
of bituminous coals are available from various publications and
cellular structure, but with reflectance ranging from slightly
websites.
greater than that of associated vitrinite to some value interme-
diate to that of the brightest fusinite. The particle size is also
5. Significance and Use
greater than 50 μm except when it occurs as a fragment within
5.1 The volume fraction of physical components of coal is
the binder matrix.
3.4.16.1 Discussion—The precise reflectance boundary be- used as an aid in coal seam correlation and in the character-
ization of coals for their use in carbonization, gasification,
tween semifusinite and fusinite has not been universally
defined, although some practitioners place the division at liquefaction, and combustion processes.
R max = 2.0 %; hence, semifusinite is somewhat vaguely de-
o
5.2 This test method is for use in scientific and industrial
fined as “fusinite with low reflectance.”
research, not compliance or referee tests.
3.4.17 sporinite, n—a liptinite maceral exhibiting various
lenticular, oval, or round forms that reflect the cross-sectioning 6. Apparatus
of a flattened, hollow, ovoid body; sometimes exhibits rod-like
6.1 Microscope—Any microscope with a mechanical stage
projections that are small relative to the size of the total body.
and a vertical illuminator (that is, metallurgical or opaque-ore
3.4.17.1 Discussion—Sporinite originated as a lipid sub-
microscope) may be used, provided that the lens combination
stance that covered, as a sk
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D2799 − 21 D2799 − 23
Standard Test Method for
Microscopical Determination of the Maceral Composition of
Coal
This standard is issued under the fixed designation D2799; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the equipment and techniques used for determining the physical composition of a coal sample in terms
of volume percentfraction of the organic components and of mineral matter, if desired. desired by systematic manual point count.
1.2 The term weight is temporarily used in this test method because of established trade usage. The word is used to mean both
force and mass and care must be taken to determine which is meant in each case (the SI unit for force is newton and for mass,
kilogram).
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D121 Terminology of Coal and Coke
D388 Classification of Coals by Rank
D2797 Practice for Preparing Coal Samples for Microscopical Analysis by Reflected Light
D2798 Test Method for Microscopical Determination of the Vitrinite Reflectance of Coal
D3174 Test Method for Ash in the Analysis Sample of Coal and Coke from Coal
D4239 Test Method for Sulfur in the Analysis Sample of Coal and Coke Using High-Temperature Tube Furnace Combustion
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E562 Test Method for Determining Volume Fraction by Systematic Manual Point Count
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions—For definitions of terms, refer to Terminology D121.
This test method is under the jurisdiction of ASTM Committee D05 on Coal and Coke and is the direct responsibility of Subcommittee D05.28 on Petrographic Analysis
of Coal and Coke.
Current edition approved Dec. 1, 2021Feb. 1, 2023. Published December 2021February 2023. Originally approved in 1969. Last previous edition approved in 2021 as
ε1
D2799 – 13D2799 – 21.(2021) . DOI: 10.1520/D2799-21.10.1520/D2799-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2799 − 23
3.2 Classification—The classification of the microscopic constituents into groups of similar properties in a given coal is as follows:
Maceral Group Maceral
Vitrinite —
Liptinite or (exinite) alginite
Liptinite alginite
cutinite
resinite
sporinite
Inertinite fusinite
inertodetrinite
macrinite
micrinite
funginite
secretinite
semifusinite
3.3 Many laboratories associated with the coke-making industry use the following simplified classification for petrographic
analysis of bituminous coal:
Maceral Group Maceral
Vitrinite vitrinite
Liptinite liptinite (other than resinite)
resinite
Inertinite semifusinite
micrinite
fusinite
mineral matter
Other organizations use different classifications.
3.4 Definitions of Terms Specific to This Standard:
3.4.1 alginite, n—a liptinite maceral that is generally spherical or ovoid, frequently having a crenulated border and somewhat
irregular reflectance and sometimes occurring in clusters reflecting an origin from Botryococcus algae.
3.4.1.1 Discussion—
Alginite often occurs as degraded fragments derived from colonial or unicellular bodies.
3.4.2 cutinite, n—a liptinite maceral in the form of a sheet reflecting its origin from leaf- or twig-covering plant cuticle, frequently
exhibiting reticulation in planar section and a serrated edge in cross section.
3.4.3 exinite, n—Deprecated term. Use preferred term liptinite; sometimes has also been used as a synonym for sporinite.
3.4.4 funginite, n—an inertinite maceral occurring as round or ovoid bodies, frequently containing voids, reflecting an origin from
fungal sclerotia; also occurs (especially in lower rank coals) as interlaced, stringy materials derived from fungal hyphae.
3.4.5 fusinite, n—an inertinite maceral distinguished principally by the preservation of some feature(s) of the plant cell wall
structure, and with a particle size greater than 50 μm except when it occurs as a fragment within the binder matrix; see also
semifusinite.
3.4.6 inertinite, n—macerals that exhibit higher reflectance than other organic substances in the coal.
3.4.6.1 Discussion—
In any coal ranked lower than anthracitic, inertinite reflectance commonly spans the range from only slightly higher than associated
vitrinite to very high reflectance (often as high as R max ≥ 6 %). In anthracitic rank coals, inertinite reflectance may be lower than
o
that of vitrinite, and is then recognized by its morphology and form of anisotropy. Highly reflecting inertinite commonly exhibits
relief on polished surface. Its name derives from the fact that most varieties behave inertly in the thermoplastic deformation during
the coking process (except in its lowest reflecting manifestation). The volatile matter yield of inertinite is lower than that of other
macerals in the same coal.
D2799 − 23
3.4.7 inertodetrinite, n—an inertinite maceral occurring as individual, angular, clastic fragments incorporated within the matrix of
other macerals (commonly vitrinite) or minerals, and in the size range from 2 μm to 50 μm.
3.4.8 liptinite, n—macerals that exhibit lower reflectance than other organic substances in a coal, appearing black to dark gray and
that fluoresce under blue to ultraviolet light in coals ranked high volatile bituminous and lower.
3.4.8.1 Discussion—
The fluorescence of liptinite distinguishes fine-grained liptinite from similar sized, low reflectance, nonfluorescing clay minerals.
Liptinite is derived principally from lipid substances forming skins (exines) and resinous secretions or exudates of plants. Liptinite
is sub-classified on the basis of morphology inherited from plant structure. In coals in which vitrinite reflectance exceeds about
1.4 %, liptinite can be indistinguishable from vitrinite. Liptinite has the highest volatile matter yield of the macerals in a coal.
3.4.9 maceral, n—an organic substance in coal that is distinguished and classified (see maceral classification) on the basis of its
optical microscopic properties.
3.4.9.1 Discussion—
Macerals originate from plant tissues, secretions, and exudates that have been altered by geological processes and may contain up
to several weight percent of inorganic elements in microscopically indistinguishable form.
3.4.10 maceral classification, n—The systematic division of the organic substances (macerals) in coal based on their appearance
in the optical microscopic.
3.4.10.1 Discussion—
Although macerals may be identified in translucent, thin sections using criteria not defined herein, this test method deals only with
identification and classification based on microscopic appearance on polished surfaces according to Practice D2797. Three major
maceral groups are recognized on the basis of relative reflectance in white light, specifically: vitrinite—moderately reflecting
(intermediate gray), liptinite—poorly reflecting (black to dark gray), and inertinite—highly reflecting (light gray to white). Each
group can be subdivided on the basis of other microscopically distinctive features such as: reflectance contrasts (relative shades
of gray); morphology, that is, shape and size (morphologic distinctions in definitions contained herein are idealized because
morphologic appearance depends on the initial form of the source material, its state of preservation, including granulation, and on
the orientation of the cross section presented on the polished preparation); spatial association with other substances; fluorescence
properties (color, intensity) in blue to ultraviolet light; relief; color tinges; internal reflections; and anisotropic properties.
Microscopic criteria provide classification capability without any implication of absolute chemical composition or physical
behavior, although some properties relative to other macerals in the same coal can be inferred broadly. Substances classified as the
same maceral by microscopic criteria can differ chemically, physically, and characteristically in coals of different ranks. Some
properties can be estimated by the measurement of reflectance (Test Method D2798).
See 3.3 for the classification used by most practitioners of this test method.
3.4.10.2 Discussion—
Microscopic criteria provide classification capability without any implication of absolute chemical composition or physical
behavior, although some properties relative to other macerals in the same coal can be inferred broadly. Substances classified as the
same maceral by microscopic criteria can differ chemically, physically, and behavioristically in coals of different ranks. Some
properties can be estimated by the measurement of reflectance (Test Method D2798).
3.4.10.3 Discussion—
See 3.3 for the classification used by most practitioners of this test method.
3.4.11 macrinite, n—an inertinite maceral, generally nonangular, exhibiting no relict plant cell wall structure and larger than 10
μm.
3.4.12 micrinite, n—an inertinite maceral, generally nonangular, exhibiting no relict plant cell wall structure, smaller than 10 μm
and most commonly occurring as particles around 1 μm to 5 μm diameter.
3.4.13 mineral matter, n—in coal, historically considered to be the non-organic fraction composed of physically discrete particles
of minerals, such as clays, quartz, pyrite, etc., and all elements other than, carbon, hydrogen, oxygen, nitrogen, and sulfur in the
organic fraction.
3.4.14 resinite, n—a liptinite maceral occurring as rounded, ovoid, or rod-like bodies assuming the shape of an enclosing cell
lumen or as irregular shapes filling cracks in the coal.
D2799 − 23
3.4.15 secretinite, n—an inertinite maceral occurring as round, ovoid, or oblong bodies, without obvious plant structure, vesicled
to non-vesicled, sometimes containing characteristic fractures, slits, or a notch.
3.4.15.1 Discussion—
Secretinite is considered to be derived by the oxidation of plant resin secretions or humic gels. Vesicular and non-vesicular
secretinite was formerly included in sclerotinite of fungal origin. Secretinite is a common maceral in medium- and high-rank
Permian and Carboniferous coals.
3.4.16 semifusinite, n—an inertinite maceral with morphology like fusinite sometimes with less distinct evidence of cellular
structure, but with reflectance ranging from slightly greater than that of associated vitrinite to some value intermediate to that of
the brightest fusinite. The particle size is also greater than 50 μm except when it occurs as a fragment within the binder matrix.
3.4.16.1 Discussion—
The precise reflectance boundary between semifusinite and fusinite has not been universally defined, although some practitioners
place the division at R max = 2.0 %; hence, semifusinite is somewhat vaguely defined as “fusinite with low reflectance.”
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3.4.17 sporinite, n—a liptinite maceral exhibiting various lenticular, oval, or round forms that reflect the cross-sectioning of a
flattened, hollow, ovoid body; sometimes exhibits rod-like projections that are small relative to the size of the total body.
3.4.17.1 Discussion—
Sporinite originated as a lipid substance that covered, as a skin, ovoid spore or pollen grains which commonly ranged from around
ten to several hundred micrometres in diameter. Sporinite often occurs as fragments derived from these initially ovoid bodies.
3.4.18 vitrinite, n—the predominant maceral in most coals of intermediate reflectance occurring as substantial volumes of more
or less uniformly reflecting material or as a matrix enclosing particles of other macerals and mineral matter or as particles or bands
intermixed with other maceral fragments.
3.4.18.1 Discussion—
Because most vitrinite is derived from the cellular, structural tissues of plants, it may exhibit relict cell structure. The reflectance
of vitrinite is related to the rank of the coal in which it is found. Reflectance increases (from around R max = 0.3 % in lignitic
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coals) in parallel with the increase in fixed carbon yield associated with increasing rank. Because many of the properties of typical
coals reflect the properties of the dominating vitrinite, it is common practice to estimate coal prop
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