Melquiades, Fábio Luiz, et al. “Chemical Characterization of Clay SRM by X-Ray Fluorescence – Results Comparison from Different Laboratories”. Semina: Ciências Exatas E Tecnológicas, vol. 30, no. 2, Dec. 2009, pp. 145-50, doi:10.5433/1679-0375.2009v30n2p145.