ISO 7404-3:2025

International
Standard
ISO 7404-3
Fourth edition
Coal — Methods for petrographic
2025-10
analysis —
Part 3:
Method of determining maceral
group composition
Charbon — Méthodes d'analyse pétrographique —
Partie 3: Méthode de détermination de la composition en groupes
de macéraux
Reference number
© ISO 2025
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 1
6 Apparatus . 2
7 Preparation of coal sample . 2
8 Procedure . 2
9 Expression of results . 3
9.1 Maceral groups .3
9.2 Individual macerals .4
10 Precision . 5
10.1 Repeatability limit .5
10.2 Reproducibility limit .5
11 Test report . 6
Annex A (informative) Sub-division of maceral groups . 7
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 7404-3:2009), 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;
— Figure 1 labelling has been updated to include the point to be counted.
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. The ICCP
also runs an accreditation program for maceral group analysis. 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 (or huminite) is a useful
measure of coal rank and the distribution of the reflectance of vitrinite (or huminite) in a coal blend, together
with a maceral group analysis, can provide information about some 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.
ISO 11760 uses the maceral group composition as one of three parameters to classify coal; the other
parameters are vitrinite reflectance and ash yield, respectively, for rank and grade.
Macerals are microscopically recognizable organic constituents of coal, and can be grouped together into
three maceral groups: vitrinite (or huminite in lower rank coal), liptinite and inertinite.
Maceral groups and their subdivisions are listed in Annex A and described in detail in ISO 7404-1. The
properties of a given coal are determined by the proportions and associations of the macerals and minerals
present and by the rank of the coal. The method of determining maceral group composition described in
this document applies to determinations made in reflected white light; the additional use of fluorescence
microscopy is recommended when analysing lower rank coals.
In addition to the macerals, it is possible to identify certain minerals in coal; these can either be determined
as separate categories or be ignored. As some of the minerals cannot be satisfactorily determined under the
microscope, an estimate of the total mineral matter content can be obtained from the ash.
Annex A of this document is for information only.

v
International Standard ISO 7404-3:2025(en)
Coal — Methods for petrographic analysis —
Part 3:
Method of determining maceral group composition
1 Scope
This document specifies a method for determining the proportions of the maceral groups (and the minerals,
if desired) in coals. It is concerned only with determinations made on polished particulate blocks using
incident white light. For lower-rank coals, the additional use of the fluorescence mode is necessary to
identify liptinites.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 7404-1, Coal — Methods for petrographic analysis — Part 1: Vocabulary
ISO 7404-2, Coal — Methods for petrographic analysis — Part 2: Method of preparing coal samples
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7404-1 apply.
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/
4 Principle
A representative sample of coal is used to prepare a particulate block in accordance with ISO 7404-2. This is
examined using a reflected light microscope and the macerals are identified under an immersion medium by
their relative reflectance, colour, size and morphology. Their proportions are determined by a point-count
procedure.
5 Reagents and materials
5.1 Immersion medium, having a suitable refractive index and compatible with the microscope objective.
It is necessary that the immersion medium does not react with either the coal or binder. It is recommenced
that an immersion medium with a refractive index of 1.5180 as described in ISO 7404-5 be used, especially if
the reflectance of the macerals is being measured.

6 Apparatus
6.1 Reflected light microscope, having an immersion objective of magnification between 25x and 60x
and an eyepiece of magnification between 8x and 12x, to ensure a minimum total magnification of 300x.
The eyepiece incorporates a fine crosshairs graticule.
6.2 Mechanical stage, capable of advancing the specimen laterally by equal steps of such length that only
a negligibly small proportion of the particles examined receives more than one count on the same particle.
The stage also permits a similar stepped advance in the perpendicular direction. The lateral movement is
actuated preferably by the counter mechanism, whereas the perpendicular movement can be satisfactorily
performed manually.
NOTE It is possible to minimize more than one count on the same particle by choosing a step length equal to
half of the maximum particle size. For example, for a particle size of 1 mm mounted in a 25 mm diameter block the
recommended step length is 0,5 mm.
6.3 Counter, capable of registering the counts in each category and the grand total of petrographic
components.
6.4 Sample mounting equipment, comprised of slides, modelling clay and a levelling device.
7 Preparation of coal sample
From a representative sample of crushed coal prepare and polish a particulate block in accordance with
ISO 7404-2.
8 Procedure
Adjust the microscope (6.1) for Köhler illumination, where the light path is focused and centred such that
it is spread evenly over the field of view, providing optimum contrast and resolution. Place the levelled
particulate block on the stage, apply the immersion
...