1. Steinmann, J. Vortr. Sitz. Böhm. Gesell. Wiss. (1825).
2. Church, A. H. Miner Mag. 11, 8–10 (1895).
3. Fisher, D. J. Am. Miner. 51, 1811–1814 (1966).
4. Moore, P. B. & Araki, T. Inorg. Chem. 16, 1096–1106 (1977).
5. Moore, P. B. 2nd int. Congr. on Phosphorus Compounds Proc. 105–130 (Institut Mondial du Phosphate, Paris, 1980).