ISO 7404-2:2025

International
Standard
ISO 7404-2
Third edition
Coal — Methods for petrographic
2025-10
analysis —
Part 2:
Method of preparing coal samples
Charbon — Méthodes d'analyse pétrographique —
Partie 2: Méthode de préparation des échantillons de charbon
Reference number
© ISO 2025
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Definitions . 1
4 Principle . 1
5 Reagents and materials . 1
6 Apparatus . 2
7 Procedure . 4
7.1 Preparation of the coal sample for making a particulate block .4
7.1.1 Sample.4
7.1.2 Drying .4
7.1.3 Size reduction . . .4
7.1.4 Sample division . . .4
7.2 Preparation of particulate block .4
7.3 Preparation of polished surface of particulate block .4
7.4 Examination of the polished surface .5
7.5 Storage prior to reflectance analysis .5
7.6 Re-examination of a particulate block .5
Annex A (informative) Examples of procedures for the preparation of a polished particulate
block suitable for petrographic analysis from a sample of crushed coal . 6
Bibliography .12

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
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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).
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This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 5, Methods
of analysis.
This third edition cancels and replaces the second edition (ISO 7404-2:2009), 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;
— clarified that ion-milling equipment is not acceptable for use in preparation of samples for reflected light
microscopy.
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 single-seam coals provide information about the rank, the maceral and
microlithotype compositions and the distribution of mineral matter 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, it can provide information about chemical and technological properties of the
coal and coal blend. Various other applications, like the characterization of bulk samples, cargoes, etc., and
the precise determination of different rank vitrinites in complex coal blends are in use.
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.
The varied petrographic composition and hardness of coal and the type and amount of included mineral
matter does not permit the formulation of a precise procedure that can be applied with equal success to all
types and ranks of coal. For example, a successful preparation method for use with medium- and high-rank
coals might not be applicable among low-rank coals. Within these limits, therefore, this document allows
the operator to apply individual skills and experience to the preparation of a satisfactory polished surface.
Nevertheless, recommended procedures that have been found applicable to a variety of coals, are given in
the Annex A, which is for information only.
Many processes are involved between the mining of the coal and its preparation for industrial use.
Petrographic analysis can be required at any stage on samples from the coal seam in situ, from borehole cores,
on the raw product from the colliery, on the products from the preparation plant, or on the final product.
The amount and size distribution of the coal being investigated thus varies widely and it is important to
ensure that the sample obtained for petrographic analysis is fully representative.

v
International Standard ISO 7404-2:2025(en)
Coal — Methods for petrographic analysis —
Part 2:
Method of preparing coal samples
1 Scope
This document specifies methods for preparing a polished particulate block from a sample of crushed
coal for analysis by reflected light microscopy. These methods can also be applied to the preparation of a
polished, embedded lump of coal.
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 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth
ISO 7404-1, Coal — Methods for petrographic analysis — Part 1: Vocabulary
ISO 18283, Coal and coke — Manual sampling
International Committee for Coal and Organic Petrology (ICCP), International Handbook of Coal Petrography
3 Definitions
For the purposes of this document, the terms and definitions given in the ICCP International Handbook of
Coal Petrography and 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 air-dried coal is crushed to a specified particle size and mixed with a suitable
binder. The mixture is formed into a particulate block, one face of which is ground and polished to give a
relief-free and scratch-free surface for analysis by reflected light microscopy.
5 Reagents and materials
5.1 Binder, used to hold the particles of crushed coal together as a particulate block, or to embed a lump
of coal.
The properties of the binder shall be such that:
a) there shall be no chemical reaction with the coal or immersion medium;

b) for liquid binders such as polyester resin, the curing temperature required to make the particulate block
should not exceed 100 °C and a temperature of less than 60 °C is preferable;
c) for thermoplastic mounting materials such as polymethyl methacrylate (PMMA) powder, a temperature
of about 120 °C is required for proper annealing, which makes it inadequate for low-rank coals;
d) the surfaces of the coal particles shall be easily wetted and there shall be good penetration of pores
and cracks;
e) the coal particles shall be held securely during grinding and polishing;
f) there shall be a marked contrast with the coal particles when immersed in medium and focused under
the reflected light microscope;
g) the hardness shall be comparable with that of the coal so that a flat, relief-free and scratch-free surface
can be obtained by grinding and polishing;
h) there shall be no large volume changes during curing, which can cause possible damage to the coal
particles;
i) the viscosity of liquid binder shall be such that the tendency of coal grains to segregate due to density
and size is minimized.
5.2 Mould release agent, that does not affect the coal and mounting compound, nor damage the mould.
5.3 Grinding abrasives, consisting of silicon carbide papers of decreasing grain size [53,5 µm (240 grit or
P280), 23,6 µm (400 grit or P800), 16,0 µm (600 grit or P1200)].
Metal-bonded, diamond-embedded 15 µ
...