1. Speight: Handbook of Coal Analysis;James,2005
2. UN ECE: International Codification System for low rank Coal Utilization , 2002.
3. UN ECE: International Codification System for medium and high rank Coals , 1988.
4. ASTM D388-15, Standard Classification of Coals by Rank, ASTM International, West Conshohocken, PA, 2015.
5. Federal Institute for Geosciences and Natural Resources, Energy Raw Materials, 2009, Hannover, Germany.