1. American Society for Testing and Materials, 1991. Annual Book of ASTM Standards. Section 5: Petroleum Products, Lubricants, and Fossil Fuels. 5.05: Gaseous Fuels: Coal and Coke.
2. The petrography, mineralogy and geochemistry of a Pliocene lignite from southern Saskatchewan;Beaton;Can. Int. J. Coal Geol.,1991
3. Clarke, L.B., Sloss, L.L., 1992. Trace elements emissions from coal combustion and gasification. IEA Coal Research Report, IEACR/49, 111 pp.
4. Energy Report, 1997. The publication of Turkish National Committee, Ankara, 70 pp.
5. On the geochemistry of strontium in Bulgarian coals;Eskenazy;Chem. Geol.,1989