ISO 7404-3:2025

Overview

ISO 7404-3:2025 - Coal - Methods for petrographic analysis - Part 3 specifies a standardized, microscope-based method for determining maceral group composition in coal. The procedure applies to polished particulate blocks examined in reflected white light; for lower‑rank coals the fluorescence mode is recommended to identify liptinites. This fourth edition updates earlier guidance (ISO 7404-3:2009) and incorporates input from the ICCP (International Committee for Coal and Organic Petrology).

Key topics and technical requirements

• Sample preparation: Use a representative, polished particulate block prepared in accordance with ISO 7404-2.
• Microscopy: Reflected‑light microscope with an immersion objective (25x–60x) and eyepiece (8x–12x) to achieve a minimum total magnification of 300x. Köhler illumination and an immersion medium (recommended refractive index ~1.5180) are required for consistent contrast and reflectance measurement.
• Point‑count procedure: Identify material under crosshairs and apply a systematic mechanical stage step to traverse the block. Boundary rules use quadrant inspection (top-right, bottom-right, bottom-left, top-left). At least 500 points should be counted (excluding minerals) to determine proportions.
• Maceral groups: Results are reported as percent volume fractions for vitrinite (huminite in low rank), liptinite, and inertinite. Minerals may be either counted as a separate category or estimated from ash-based empirical relationships (Parr formula referenced).
• Counting controls: Use a graticule crosshair and a counter to register categories. Step length guidance reduces repeated counts on the same particle (example: step ~half the maximum particle size).
• Reporting: Indicate whether minerals were counted or calculated, the number of points, and the procedure followed.

Applications and users

ISO 7404-3:2025 is used by:

• Petrographic laboratories and accredited analysts
• Coal producers and quality control teams
• Power generation and coking coal assessment groups
• Geological and research organizations studying coal rank, continuity and composition
• Regulatory and standards bodies using maceral composition for coal classification (ISO 11760 references maceral group composition as a classification parameter)

Practical applications include characterizing coal rank and blend behavior, predicting technological properties, supporting coal classification, and providing consistent laboratory data for product specifications.

Related standards

• ISO 7404-1 - Vocabulary for petrographic analysis
• ISO 7404-2 - Sample preparation (particulate block)
• ISO 7404-5 - Guidance on immersion media and reflectance measurement
• ISO 11760 - Coal classification (uses maceral group composition)

Keywords: ISO 7404-3:2025, coal petrographic analysis, maceral group composition, point-count procedure, reflected light microscope, vitrinite, liptinite, inertinite, immersion medium, coal classification.