1. Becker P. Phosphates and Phosphoric Acid, Raw Materials, Technology and Economics of the Wet Process. 2nd ed. New York, Basel: Marcel Dekker Inc; 1989. p. 740
2. Naray-Szabo S. The structure of apatite (CaF)Ca4(PO4)3. Zeitschrift für Kristallographie. 1930;75:387
3. Mehmel M. Zeitschrift für Kristallographie. 1930;75:323
4. Elliott J. Structure and Chemistry of the Apatites and Other Calcium Orthophosphates. Amsterdam, London: Elsevier; 1994. p. 389
5. Gottschall AJ. Journal of South Africa. 1958;II:45