ISO 7404-1:2025

Overview

ISO 7404-1:2025 - Coal - Methods for petrographic analysis - Part 1: Vocabulary is the fourth edition of the ISO vocabulary for coal petrography. This document defines the core terms used in maceral and microlithotype analyses and in the determination of vitrinite reflectance. It applies to the microscopic examination of coal of all ranks and types and complements the other parts of the ISO 7404 series. The 2025 revision incorporates input from the International Committee for Coal and Organic Petrology (ICCP), adds and updates terms, and restructures supporting information in Annex A.

Key topics and requirements

• Clear definitions of fundamental petrographic concepts:
  • Coal, coalification, rank (low, medium, high) with associated vitrinite reflectance ranges (e.g., medium rank ~0.5–2% Rr, high rank ~2–6% Rr, as used in the standard).
  • Maceral groups (vitrinite/huminite, liptinite, inertinite) and maceral varieties.
  • Microlithotype definitions, including the minimum layer width (50 µm) and compositional thresholds (monomaceral ≥95% mineral-free basis; bimaceral/trimaceral criteria and impurity limits).
• Terms related to optical microscopy and reflectance measurement:
  • Reflectance, random reflectance, maximum reflectance, parasitic reflection, reflectance standard, zero standard; measurement under oil immersion in reflected-light microscopy is specified in the vocabulary.
  • Clarification that the term “random reflectance” replaces older terms such as “mean reflectance.”
• Definitions for sample preparation and observation:
  • Particulate block, lump section, point (for microscopical analysis).
• Definitions for mineral–organic intergrowths:
  • Carbominerite and minerite with quantitative mineral proportion thresholds (e.g., carbominerite: 20–60% silicate/carbonate minerals or 5–20% sulfides; minerite: >60% minerals or sulfide >20%).
• Annex A (informative) provides classification tables for macerals, microlithotypes and carbominerites.

Practical applications

• Standardizes terminology for coal petrographic analysis, ensuring consistent reporting across laboratories, research, and industry.
• Supports coal quality assessment for:
  • Power generation and utility fuel specification
  • Coking coal evaluation and metallurgical applications
  • Geological interpretation (coal rank, depositional type, lateral/vertical variation)
  • Research in organic petrology and coal geochemistry
• Useful for calibration and interpretation of vitrinite reflectance data used in rank determination, maturity studies and blend characterization.

Who should use this standard

• Coal petrologists and laboratory technicians performing maceral, microlithotype and reflectance analyses
• Geologists, mining engineers and quality control specialists in coal and coke industries
• Research institutions, regulatory bodies and standards committees implementing consistent coal petrography vocabulary

Related standards

• ISO 7404 series (other parts covering petrographic methods)
• ISO 11760 (referenced for rank classifications)
• ICCP recommendations (used as an authoritative source for petrographic nomenclature)

Keywords: ISO 7404-1:2025, coal petrographic analysis, vitrinite reflectance, maceral, microlithotype, carbominerite, coal rank, coal petrography vocabulary.