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