Overview
ISO 7404-4:2025 - Coal - Methods for petrographic analysis - Part 4 specifies a standardized point-count method for determining the proportions of microlithotypes, carbominerite and minerite in coal. The method uses a graticule with 20 crossline intersections on polished particulate blocks observed in reflected white light, with optional blue/blue‑violet/UV excitation to assist liptinite identification by fluorescence (useful for low‑rank coals).
Key topics and technical requirements
- Sampling & preparation: Analysis applies to polished particulate blocks prepared in accordance with ISO 7404-2.
- Optical setup: Reflected‑light microscope with immersion objective (25×–60×) and eyepiece (8×–12×) that accepts a graticule; immersion medium with suitable refractive index (recommended n = 1.5180 as per ISO 7404-5).
- Graticule/grid: A 20‑intersection grid with an effective 50 µm distance between extreme intersections in x and y directions, ensuring compliance with the 5% volume fraction and 50 µm minimum size rules for microlithotype identification.
- Point count rules:
- A point is accepted only if at least 10 of the 20 intersections fall on a single particle; points with fewer intersections are recorded as rejected.
- Rejected points must not exceed 10% of total accepted + rejected points; excess fines indicate poor sample preparation.
- Mineral-matter thresholds: Table-based limits define when a particle is a microlithotype versus a carbominerite or minerite (e.g., for 16–20 intersections within a particle, up to 3 intersections on carbonate/clay/quartz permitted; sulfide intersections must be 0).
- Microlithotype definitions: Allocation rules for vitrite, liptite, inertite, clarite, durite, vitrinertite and trimacerite based on distribution of maceral groups under intersections (see ISO 7404-3 for maceral ID).
- Stage movement & counting: Mechanical/scanning stage advances in steps (step length ≈ half maximum particle diameter; example 0.5–0.6 mm for 1 mm top size) to avoid double counting. Results and precision (repeatability/reproducibility) are reported.
Applications and users
ISO 7404-4:2025 is used by:
- Coal petrologists and analytical laboratories performing coal petrographic analysis
- Geologists and mining engineers for seam correlation, coal genesis studies and stratigraphic work
- Coal preparation and quality control teams to assess hardness, density, mineral content and behavior in processing and combustion
- Researchers evaluating maceral associations and their influence on coal utilization
Practical benefits include consistent microlithotype quantification for process modelling, quality assurance, and comparative studies across laboratories.
Related standards
- ISO 7404-1: Vocabulary for coal petrography
- ISO 7404-2: Sample preparation (particulate block preparation)
- ISO 7404-3: Maceral group identification and composition
- ISO 7404-5: Recommendations for immersion media and reflectance measurement
Keywords: ISO 7404-4:2025, coal petrographic analysis, microlithotype, carbominerite, minerite, graticule, point count, reflected light microscope, liptinite, vitrinite, inertinite.
Open preview (PDF)Coal — Methods for petrographic analysis — Part 4: Method of determining microlithotype, carbominerite and minerite composition