ISO 7404-4:2017

Overview

ISO 7404-4:2017 - Methods for the petrographic analysis of coals (Part 4) defines a standardized point-count procedure for determining the proportions of microlithotypes, carbominerite and minerite in coal. The method uses a graticule with 20 crossline intersections on polished particulate blocks examined under reflected white light (≈400–700 nm). Optional blue/blue‑violet or UV excitation (365–440 nm) can be used to enhance liptinite identification in low‑rank coals.

Key topics and technical requirements

• Sample preparation and materials: Analysis is performed on polished particulate blocks prepared per ISO 7404-2 and examined in an immersion medium compatible with the objective (immersion oil specified if reflectance is also required, per ISO 7404-5).
• Instrumentation:
  • Reflected‑light microscope with immersion objective (×25–×60) and eyepiece (×8–×12) capable of accepting the graticule.
  • Graticule grid with 20 intersections spaced to cover 50 µm between extreme intersections on the specimen.
  • Mechanical or scanning stage that advances by controlled steps (step-length ≈ half maximum particle diameter; e.g., 0.5–0.6 mm for 1 mm top size).
  • Counter/computer to record point counts.
• Point‑count rules:
  • A point is accepted only if ≥10 intersections of the 20 fall on a single particle.
  • Rejected points (where <10 intersections hit a particle) must not exceed 10% of total accepted + rejected points; otherwise sample re‑preparation is advised.
  • Microlithotype identity is assigned from maceral groups visible under the grid (e.g., vitrite, liptite, inertite, clarite, durite, vitrinertite, trimacerite).
• Mineral content rules:
  • Tables in the standard specify maximum allowable intersections on carbonate/clay/quartz and sulfide for classifying a point as a microlithotype, carbominerite, carbopolyminerite or minerite.
• Reporting and precision: The standard includes required expressions of results, repeatability/reproducibility guidance, and test report content.

Applications and users

ISO 7404-4:2017 is used for:

• Coal quality assessment, coal seam correlation and geological characterization.
• Coal preparation and beneficiation decisions (hardness, density, middlings/reject identification).
• Research on maceral associations and their influence on combustion, coking and mechanical behavior. Typical users include coal petrographers, laboratory analysts, mining and coal preparation engineers, research institutions, and regulatory testing laboratories.

Related standards

• ISO 7404-1 - Vocabulary for petrographic analysis of coals
• ISO 7404-2 - Sample preparation methods (particulate blocks)
• ISO 7404-3 & ISO 7404-5 - Related petrographic identification and reflectance methods
• The ISO 7404 series - comprehensive framework for coal petrography

Keywords: ISO 7404-4:2017, petrographic analysis of coals, microlithotype, carbominerite, minerite, graticule, reflected light microscope, coal petrography.