1. A Textbook of Mineralogy;Dana,1932
2. Phosphate Minerals,1984
3. On the dimorphy between the variscite and clinovariscite group: refined finestructural relationship of strengite and clinostrengite, Fe(PO4),2H2O;Taxer;Cryst. Res. Technol.,2004
4. The Microscopic Determination of the Nonopaque Minerals;Larsen,1934
5. Standard Methods for the Examination of Water and Wastewater, 13th ed., American Public Health Association, Washington, DC (1971) p. 190.