ISO 7404-4:2025

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.