ISO/FDIS 7404-1
(Main)Coal — Methods for petrographic analysis — Part 1: Vocabulary
Coal — Methods for petrographic analysis — Part 1: Vocabulary
ISO 7404-1:2016 defines terms that are used in connection with both maceral and microlithotype analyses, and with the determination of the reflectance of vitrinite. It applies to the terms used in the examination of coal of all ranks. ISO 7404-1:2016 is not intended to be a comprehensive glossary of coal petrographic terminology, nor does it attempt to provide sufficient information to allow recognition of all the coal components described. Further information may be obtained from the relevant ICCP publications[3][4][5].
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Coal — Methods for petrographic
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FINAL DRAFT
International
Standard
ISO/TC 27/SC 5
Coal — Methods for petrographic
Secretariat: SA
analysis —
Voting begins on:
Part 1:
Vocabulary
Voting terminates on:
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
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BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
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INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
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TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
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TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
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Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative References . 1
3 Terms and definitions . 1
3.1 General .1
3.2 Terms related to optical microscopy .2
3.3 Terms related to petrography .3
Annex A (informative) Classification of macerals, microlithotypes and carbominerites . 5
Bibliography . 7
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 27, Coal and coke Subcommittee SC 5, Methods
of analysis.
This fourth edition cancels and replaces the third edition (ISO 7404-1:2016), which has been technically
revised.
The main changes are as follows:
— input from the International Committee for Coal and Organic Petrology (ICCP) has been added;
— several terms and definitions have been added or modified;
— information supporting the vocabulary has been restructured as Annex A.
A list of all parts in the ISO 7404 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Petrographic analyses have been recognized internationally as important in the context of the genesis,
vertical and lateral variation, continuity, metamorphism and usage of coal. The International Committee
for Coal and Organic Petrology (ICCP) has made recommendations concerning nomenclature and analytical
[1][2][3][4][5][6]
methods and has described in detail the characteristics of a wide range of coals. This document
incorporates many useful comments made by members of the ICCP and by member bodies of ISO/TC 27.
Petrographic analyses of a single coal provide information about the rank, the maceral and microlithotype
compositions and the distribution of minerals in the coal. The reflectance of vitrinite is a useful measure
of coal rank and the distribution of the reflectance of vitrinite in a coal blend, together with a maceral
group analysis, can provide information about the rank and type of the coal and important chemical and
technological properties of the blend.
The ISO 7404 series is concerned with the methods of petrographic analysis currently employed in
characterizing coal in the context of its technological or geological use, or both. It establishes a system for
petrographic analysis.
This document is intended for use solely in connection with the generally accepted international methods of
petrographic analysis of coal described in the other parts of the ISO 7404 series.
The petrographic terms listed herein are those used by the ICCP and ISO. They do not include terms such
as, for example, pseudovitrinite, semi-vitrinite and semi-inertinite which refer to types of maceral with
particular properties, but which are sometimes difficult to define. Such terms can be considered important
for specific applications, but their wider use is not recommended.
v
FINAL DRAFT International Standard ISO/FDIS 7404-1:2025(en)
Coal — Methods for petrographic analysis —
Part 1:
Vocabulary
1 Scope
This document defines terms that are used in connection with both maceral and microlithotype analyses,
and with the determination of the reflectance of vitrinite. It applies to the terms used in the examination of
coal of all ranks and types.
This document is not intended to be a comprehensive glossary of coal petrographic terminology, nor does it
attempt to provide sufficient information to allow recognition of all the coal components described.
2 Normative References
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 General
3.1.1
coal
combustible sedimentary rock formed from bio- and geochemically altered plant remains consolidated
under superimposed strata
Note 1 to entry: The characteristics of different coals are due to differences in source plant material, in the conditions
and the degree of change that the material has undergone in its geological history and in the range of impurities
present. Coal composition can be characterized microscopically by maceral and microlithotype compositions.
3.1.2
coal type
relates to the depositional origin and the maceral–mineral admixture resulting from that origin and can be
subdivided in humic and sapropelic coals
[ ].
Note 1 to entry: Humic coals develop from peat, and sapropelic coals develop from organic mud 7 The coal type is
established through maceral (3.3.1) analysis.
3.1.3
coalification
process by which sedimented plant remains are transformed into coal (3.1.1)
Note 1 to entry: This process is characterized by an increase in the carbon mass fraction in the plant remains and
a decrease in the yield of volatile matter from the plant remains. As coalification proceeds, the reflectances (3.2.1)
of the macerals (3.3.1) increase. Vitrinite is used as a reference material for the determination of the rank (3.1.4) of
coal because its reflectance indirectly reflects the depth of burial and geothermal gradient prevailing at the time of
coalification although heat from igneous intrusion and hydrothermal fluids can also be an influence.
3.1.4
rank
position of a coal (3.1.1) in the coalification (3.1.3) series from low rank coal (3.1.5) to high rank coal (3.1.7),
indicating maturity in terms of chemical and physical properties
3.1.5
low rank coal
coal (3.1.1) that, are characterized by high inherent moisture, high volatile matter, low calorific value and a
low vitrinite reflectance
Note 1 to entry: Low rank coals were formerly often referred to as lignite (now low rank C and C) and subbituminous
coal (now low rank A). Regionally, also terms like brown coal were used for coals with a random vitrinite reflectance
below 0,5 % R . Where R refers to random vitrinite reflectance.
r r
Note 2 to entry: Low rank coals are non-agglomerating.
Note 3 to entry: See ISO 11760.
3.1.6
medium rank coal
coals (3.1.1) between high rank coal (3.1.7) and low rank coal (3.1.5)
Note 1 to entry: The vitrinites in all coals of medium rank melt and form semi-coke when coal is heated in the absence
of oxygen above 360 °C to 380 °C. Medium rank coals were formerly referred to as bituminous coals. Their random
vitrinte reflectance, R %, lies between 0,5 % and 2 %.
r
Note 2 to entry: See ISO 11760.
3.1.7
high rank coal
coal (3.1.1), with a low volatile matter and a semi-metallic lustre, and which does not soften or swell when heated
Note 1 to entry: High rank coals were formerly referred to as anthracites. Their random vitrinite reflectance, R %, lies
r
between 2 % and 6 %.
3.2 Terms related to optical microscopy
3.2.1
reflectance
percentage of the near-normal incident light reflected from a polished surface of a coal maceral
Note 1 to entry: For the purposes of this document, reflectance refers to measurements made on coal with a reflected
light microscope under oil immersion.
3.2.2
maximum reflectance
highest value of reflectance (3.2.1) measured when any polished section of a particle or lump of coal (3.1.1) is
rotated in its own plane in linearly polarized light
Note 1 to entry: Alternatively, a computer-controlled and rotated through 360° gear-coupled polarizer can be used.
3.2.3
random reflectance
reflectance (3.2.1) of any polished section of a particle or a lump of coal (3.1.1) when determined in non-
polarized light without rotation of the specimen
Note 1 to entry: The term “random reflectance” has replaced the old terms “mean reflectance” and “average
reflectance” to avoid confusion, mainly with the use of "mean” for data presenting the mean of the required number of
reflectance readings as in, for example, ”mean random reflectance”.
3.2.4
parasitic reflection
percentage of the incident light reaching the measuring device from lens boundary faces and other reflecting
surfaces in the reflected-light microscope
3.2.5
reflectance standard
polished surface of an isotropic material of known reflec
...
ISO/TC 27/SC 05 5
Secretariat: SA
Date: 2025-06-0307-14
Coal - — Methods for petrographic analysis —
Part 1:
Vocabulary
FDIS stage
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative References . 1
3 Terms and definitions . 1
3.1 General . 1
3.2 Terms related to optical microscopy . 2
3.3 Terms related to petrography . 3
Annex A (informative) Classification of macerals, microlithotypes and carbominerites . 6
Bibliography . 8
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 27, Coal and coke Subcommittee SC 5, Methods
of analysis.
This fourth edition cancels and replaces the third edition (ISO 7404-1:2016), which has been technically
revised.
The main changes are as follows:
— — input from the International Committee for Coal and Organic Petrology (ICCP) has been added;
— — several terms and definitions have been added or modified;
— — document has been restructured to information supporting the vocabulary to a normative annex has
been restructured as required by ISO/IEC Directives Part 2, 11.5.2Annex A.
A list of all parts in the ISO 7404 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Petrographic analyses have been recognized internationally as important in the context of the genesis, vertical
and lateral variation, continuity, metamorphism and usage of coal. The International Committee for Coal and
Organic Petrology (ICCP) has made recommendations concerning nomenclature and analytical methods and
[1][2][3][4][5][6[1][2][3][4][5][6] ]
has described in detail the characteristics of a wide range of coals. . This document
incorporates many useful comments made by members of the ICCP and by member bodies of ISO/TC 27.
Petrographic analyses of a single coal provide information about the rank, the maceral and microlithotype
compositions and the distribution of minerals in the coal. The reflectance of vitrinite is a useful measure of
coal rank and the distribution of the reflectance of vitrinite in a coal blend, together with a maceral group
analysis, can provide information about the rank and type of the coal and important chemical and
technological properties of the blend.
The ISO 7404 series is concerned with the methods of petrographic analysis currently employed in
characterizing coal in the context of its technological or geological use, or both. It establishes a system for
petrographic analysis.
This document is intended for use solely in connection with the generally accepted international methods of
petrographic analysis of coal described in the other parts of the ISO 7404 series.
The petrographic terms listed herein are those used by the ICCP and ISO. They do not include terms such as,
for example, pseudovitrinite, semi-vitrinite and semi-inertinite which refer to types of maceral with particular
properties, but which are sometimes difficult to define. Such terms can be considered important for specific
applications, but their wider use is not recommended.
v
Coal - — Methods for petrographic analysis —
Part 1:
Vocabulary
1 Scope
This document defines terms that are used in connection with both maceral and microlithotype analyses, and
with the determination of the reflectance of vitrinite. It applies to the terms used in the examination of coal of
all ranks and types.
This document is not intended to be a comprehensive glossary of coal petrographic terminology, nor does it
attempt to provide sufficient information to allow recognition of all the coal components described.
2 Normative References
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 General terms
3.1.1 3.1.1
coal
combustible sedimentary rock formed from bio- and geochemically altered plant remains consolidated under
superimposed strata
Note 1 to entry: The characteristics of different coals are due to differences in source plant material, in the conditions
and the degree of change that the material has undergone in its geological history and in the range of impurities present.
Coal composition can be characterized microscopically by maceral and microlithotype compositions.
3.1.2 3.1.2
coal type
relates to the depositional origin and the maceral–mineral admixture resulting from that origin and can be
subdivided in humic and sapropelic coals
[7[7].].
Note 1 to entry: Humic coals develop from peat, and sapropelic coals develop from organic mud The coal type is
established through maceral (3.3.1(3.3.1)) analysis.
3.1.3 3.1.3
coalification
process by which sedimented plant remains are transformed into coal (3.1.1(3.1.1))
Note 1 to entry: This process is characterized by an increase in the carbon mass fraction in the plant remains and a
decrease in the yield of volatile matter from the plant remains. As coalification proceeds, the reflectances (3.2.1(3.2.1)) of
the macerals (3.3.1(3.3.1)) increase. Vitrinite is used as a reference material for the determination of the rank
(3.1.4(3.1.4)) of coal because its reflectance indirectly reflects the depth of burial and geothermal gradient prevailing at
the time of coalification although heat from igneous intrusion and hydrothermal fluids can also be an influence.
3.1.4 3.1.4
rank
position of a coal (3.1.1(3.1.1)) in the coalification (3.1.3(3.1.3)) series from low rank coal (3.1.5(3.1.5)) to high
rank coal (3.1.7(3.1.7),), indicating maturity in terms of chemical and physical properties
3.1.5 3.1.5
low rank coal
coal (3.1.1(3.1.1)) that, are characterized by high inherent moisture, high volatile matter, low calorific value
and a low vitrinite reflectance
Note 1 to entry: Low rank coals were formerly often referred to as lignite (now low rank C and C) and subbituminous
coal (now low rank A). Regionally, also terms like brown coal were used for coals with a random vitrinite reflectance
below 0,5 % Rr. Where Rr refers to random vitrinite reflectance.
Note 2 to entry: Low rank coals are non-agglomerating.
[8]
Note 3 to entry: See ISO 11760 .
3.1.6 3.1.6
medium rank coal
coals (3.1.1(3.1.1)) between high rank coal (3.1.7(3.1.7)) and low rank coal (3.1.5(3.1.5))
Note 1 to entry: The vitrinites in all coals of medium rank melt and form semi-coke when coal is heated in the absence of
oxygen above 360 °C to 380 °C. Medium rank coals were formerly referred to as bituminous coals. Their random vitrinte
reflectance, Rr %, lies between 0,5 % and 2 %.
[8]
Note 2 to entry: See ISO 11760 .
3.1.7 3.1.7
high rank coal
coal (3.1.1(3.1.1),), with a low volatile matter and a semi-metallic lustre, and which does not soften or swell
when heated
Note 1 to entry: High rank coals were formerly referred to as anthracites. Their random vitrinite reflectance, R %, lies
r
between 2 % and 6 %.
3.2 3.2 OpticalTerms related to optical microscopy terms
3.2.1 3.2.1
reflectance
percentage of the near-normal incident light reflected from a polished surface of a coal maceral
Note 1 to entry: For the purposes of this document, reflectance refers to measurements made on coal with a reflected
light microscope under oil immersion.
3.2.2 3.2.2
maximum reflectance
highest value of reflectance (3.2.1(3.2.1)) measured when any polished section of a particle or lump of coal
(3.1.1(3.1.1)) is rotated in its own plane in linearly polarized light
Note 1 to entry: Alternatively, a computer-controlled and rotated through 360° gear-coupled polarizer can be used.
3.2.3 3.2.3
random reflectance
reflectance (3.2.1(3.2.1)) of any polished section of a particle or a lump of coal (3.1.1(3.1.1)) when determined
in non-polarized light without rotation of the specimen
Note 1 to entry: The term “random reflectance” has replaced the old terms “mean reflectance” and “average reflectance”
to avoid confusion, mainly with the use of "mean” for data presenting the mean of the required number of reflectance
readings as in, for example, ”mean random reflectance”.
3.2.4 3.2.4
parasitic reflection
percentage of the incident light reaching the measuring device from lens boundary faces and other reflecting
surfaces in the reflected-light microscope
3.2.5 3.2.5
reflectance standard
polished surface of an isotropic material of known reflectance (3.2.1(3.2.1)) which is used for calibrating
reflectance-measuring equipment
3.2.6 3.2.6
zero standard
non-reflecting standard used for calibrating reflectance-measuring equipment
3.2.7 3.2.7
particulate block
solid block consisting of particles of crushed coal (3.1.1(3.1.1)) representative of the sample when prepared
accordingly, bound in resin, cast in a mould and with one face ground and polished
3.2.8 3.2.8
lump section
piece of coal (3.1.1(3.1.1)) of size suitable for polishing and examination under the microscope
Note 1 to entry: One face of the lump section, usually that perpendicular to the bedding plane, is ground and polished.
3.2.9 3.2.9
point
area overlain by the intersection of the cross hair in the eyepiece graticule or on the computer monitor during
microscopical analysis
3.3Petrographic terms
3.3.1
3.3 Terms related to petrography
3.3.1
maceral
microscopically recognizable organic constituent of coal (3.1.1(3.1.1)) analogous to the minerals of inorganic
rocks, but without a characteristic crystal form and inconstant in chemical composition
Note 1 to entry: The macerals are distinguished from one another microscopically on the basis of their differences in such
properties as reflectance (3.2.1(3.2.1),), colour, fluorescence, morphology, size and hardness. They originate from the
remains of different tissues of plants and their physical and chemical properties change as coalification (3.1.3(3.1.3))
...
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