1. Kirk-Othmer. Encyclopedia of chemical technology, 3rd edn, vols. 1–16; 2nd Edn, vols. 14–23
2. US Bureau of Mines. Minerals yearbook, US Govt. Printing Office (annual)
3. Batelle-Columbus Laboratories. ‘Energy use patterns in metallurgical and non-metallic mineral processing’, (Phases 4, 5 and 6) Publ. US Dept. Commerce, (NTIS PB 245749) 1975 and 1976
4. — Metal statistics, Metallgesellschaft Frankfurt (annual)
5. ‘Non-fuel minerals data base’;Crowson,1980