Pańczyk, Magdalena, et al. “Application of Handheld XRF Spectrometers for Estimation of Rare Earth Elements Content in Alkaline Intrusions from the East European Craton (NE Poland) – Preliminary Results”.
Geology, Geophysics and Environment, vol. 41, no. 1, Aug. 2015, p. 120,
https://doi.org/10.7494/geol.2015.41.1.120.