1. Le Bas, M. J. Carbonatite-Nephelinite Volcanism, 387 (Wiley, London, 1977).
2. King, B. C. J. Petrol. 6, 67 (1965).
3. Heinrich, E. W. The Geology of Carbonatites, 555 (Rand, McNally, Chicago, 1966).
4. Cruft, E. F., Ingamells, C. D. & Muysson, J. Geochim. cosmochim. Acta 29, 581 (1965).
5. Nash, W. P. Am. Miner. 57, 877 (1972).