by Verwoerd, W.J., Viljoen, E.A., Chevallier, L.
Published in Journal of African earth sciences (1994) (01.07.1995)

by De Waal, S. A, Viljoen, E. A
Published in The American mineralogist (1971)

by Buchanan, D. L., Nolan, J., Viljoen, E. A.
Published in Contributions to mineralogy and petrology (01.08.1980)

by Amthauer, G., McIver, J. R., Viljoen, E. A.
Published in Physics and chemistry of minerals (1979)