1. Minerals Yearbook, 1969.
2. The Platinum Metals, Mineral Resources Div, Dept of Mines and Technical Surveys, Ottawa, Mineral Report 3, 1960.
3. H Quiring, Platinmetalle, 1962 ( Ferdinand Enke Verlag, Stuttgart).
4. W Noddack, I Tacke and O Berg, Phys Ber 1925, 6, 1669.
5. S R Zimmerly and J D Prater, US Patent 2,876,065 (1957).