Dr Viljoen gained his Master's degree in Geochemistry at the University of Cape Town, and a PhD from the University of the Witwatersrand's Bernard Price Institute for his research on isotope geochemistry in relation to geological processes and the crystallisation of diamonds. He started his career as a field geologist based at the then newly-discovered Venetia kimberlite cluster in Limpopo Province, and subsequently worked at the De Beers Kimberlite Petrology Unit in Kimberley and the Geoscience Centre in Johannesburg. He has more than 24 years' experience in mantle geochemistry, indicator mineral chemistry and interpretation, and diamond provenance and genesis, and has authored or co-authored more than 30 technical publications in international peer-reviewed journals.