Overview
ISO 7404-3:2009 specifies a standardized petrographic method for determining the maceral group composition of coals. The procedure applies to polished particulate blocks examined under reflected white light (incident light microscopy) and - for lower‑rank coals - the additional use of fluorescence microscopy to identify liptinites. The standard defines the point‑count procedure, minimum counting requirements, microscope and immersion oil requirements, result expression and precision expectations for maceral group analysis.
Key topics and requirements
- Sample preparation: Use a polished particulate block prepared according to ISO 7404-2.
- Microscopy: Reflected light microscope with immersion objective (25×–60×) and eyepiece (8×–12×) to give at least 300× total magnification; Köhler illumination and a crosshair graticule are required.
- Immersion medium: Use a non‑reactive immersion oil of suitable refractive index (recommendation: about 1.518) compatible with objectives and binders.
- Point‑count method: Identify maceral under the crosshairs and record counts for vitrinite (huminite in low rank), liptinite, and inertinite. Count at least 500 points excluding minerals. Use the prescribed procedure for handling boundaries, mounting medium and pores.
- Mineral handling: Minerals may be ignored, counted as a separate category, or their volume fraction calculated from ash content using empirical relationships; any chosen procedure must be reported.
- Results and precision: Express maceral group percentages as volume fractions (nearest integer or one decimal). The standard provides guidance on theoretical standard deviation, repeatability and reproducibility limits based on binomial statistics and observed analyst variation.
- Reporting: Test report must reference ISO 7404-3, sample identification, lab details, date, number of points counted, mineral handling method (or equation used), results and relevant observations.
Applications and users
ISO 7404-3:2009 is used by:
- Coal petrographers and analytical laboratories performing routine coal characterization and quality control.
- Research organizations studying coal genesis, rank and lateral/vertical variability.
- Power plants, coking and metallurgical industries, and coal traders assessing coal blends and technological properties.
- Regulatory and standards bodies/classification programs (supports ISO 11760 coal classification and ICCP accreditation).
Practical uses include coal classification, estimating blend behaviour, correlating maceral composition with combustion, coking or conversion performance, and identifying mineral matter distribution.
Related standards
- ISO 7404-1 - Vocabulary for petrographic analysis
- ISO 7404-2 - Preparation of coal samples (particulate blocks)
- ISO 11760 - Classification of coals
Keywords: ISO 7404-3:2009, maceral group composition, petrographic analysis of coals, reflected white light, point count, vitrinite, liptinite, inertinite, coal petrography.