Varga, P., J. Lexa, P. Uhlík, and M. Rajnoha. “Characterization of Perlites from Jastrabá and Lehôtka Pod Brehmi Deposits”. Geology, Geophysics and Environment, vol. 41, no. 1, Aug. 2015, p. 146, doi:10.7494/geol.2015.41.1.146.