ISO 7404-4:2025

International
Standard
ISO 7404-4
Third edition
Coal — Methods for petrographic
2025-10
analysis —
Part 4:
Method of determining
microlithotype, carbominerite and
minerite composition
Charbon — Méthodes d'analyse pétrographique —
Partie 4: Méthode de détermination de la composition en
microlithotypes, carbominérites et minérites
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Material. 2
6 Apparatus . 2
7 Procedure . 3
8 Expressions of results . 5
9 Precision . 6
9.1 Repeatability limit .6
9.2 Reproducibility limit .7
10 Test report . 7
Bibliography . 9

iii
Foreword
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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 7404-4:2017), 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.
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 described in detail the characteristics of a wide range of coals .
Petrographic analyses of a single coal 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, 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.
Microlithotypes are the naturally occurring associations of macerals which characterize the microscopically
visible different types of coal. By convention, the identity of a microlithotype is determined by the maceral
group or groups occurring within an area of at least 50 μm × 50 μm and which are present in amounts equal
to or exceeding a volume fraction of 5 %. Hence, they can comprise a single maceral or maceral group if it
exceeds these dimensions. Microlithotypes may include up to 20 % by volume fraction of minerals such as
clay, quartz and carbonates or up to 5 % by volume fraction of sulfide minerals. If the volume fraction of
mineral matter exceeds these amounts, the material is designated as minerite or carbominerite depending
on the proportions of coal and mineral matter.
Carbominerites can be subdivided according to the type of mineral matter.
Microlithotypes contribute information on the genesis of coal seams and can assist in solving problems of
seam correlation. Because they determine, together with rank and mineral matter, the hardness and density
of the bulk coal substance, microlithotypes affect the behaviour of coal in mining and coal preparation
processes. The different microlithotypes determine, under given geological conditions, the distribution of
micro-cracks and to some extent the cleat in the coal. The results of maceral analyses can be interpreted
more meaningfully from a knowledge of microlithotype composition. Such information can assist in
explaining the behaviour of coal in commercial and experimental utilization processes where the association
of macerals is known to be important.
NOTE 1 The volume fraction expressed as a per cent of carbonate, clay and quartz minerals on the one hand and
sulfide minerals on the other, which define the carbominerites and minerites, correspond to the densities which
separate acceptable coal from middlings (1,5 g/cm ) and from rejects in coal preparation.
NOTE 2 A cleat in coal refers to the naturally occurring orthogonal joints in coal. Cleats occur as two perpendicular
sets of fractures.
v
International Standard ISO 7404-4:2025(en)
Coal — Methods for petrographic analysis —
Part 4:
Method of determining microlithotype, carbominerite and
minerite composition
1 Scope
This document specifies a method, using a graticule with 20 crossline intersections, for determining the
proportions of microlithotypes, carbominerite and minerite in coals. It applies only to determinations made
on polished particulate blocks using reflected white light. Additional blue, blue-violet or UV light excitation
for better identification of liptinite in fluorescence can be used especially for low rank coals.
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: Methods of preparing coal samples
ISO 7404-3, Coal — Methods for petrographic analysis of coals — Part 3: Method of determining maceral group
composition
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7404-1 and the following 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/
3.1
point
observation of a portion of the particulate block through the eyepiece graticule made during the analysis
Note 1 to entry: The allocation of a point to a particular microlithotype, or to carbominerite or minerite, is determined
by the macerals and/or mineral matter present at the 20 intersections of the graticule. A point is only counted if at
least 10 intersections fall on a particle, if less than 10 intersections fall upon a particle (i.e. fall upon binder material)
the point is rejected but recorded separately and the mechanical stage is advanced one step.
4 Principle
Examination by using a reflected light microscope and point count procedure of a representative sample
of coal prepared as a particulate block in accordance with ISO 7404-2. Identification under an immersion
medium of the microlithotypes from their maceral composition. The proportions of the macerals are
determined using a graticule having a grid with 20 points of intersection spaced to define a distance of 50 μm

on the specimen between extreme intersections in the x (abscissa) and y (ordinate) directions, respectively.
The use of such a graticule allows the analyst to comply with the 5 % minimum volume fraction and 50 μm
minimum size stipulation.
NOTE Alternatively, a graticule of equivalent size can be used on a computer screen
5 Material
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 recommended
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 25× and 60×
and eyepiece of magnification between 8× and 12×. The eyepiece shall have the facility for inserting a
graticule.
6.2 Graticule, inscribed with a grid having 20 crossline intersections according to the pattern shown in
Figure 1. The effective distance between extreme intersections in the x- and y-directions, respectively, is 50 μm.
Key
1 50 μm on the specimen
Figure 1 — Design of grid for microlithotype an
...