A natural specimen from the deposit at Kucin (Slovakia), rich in clinoptilolite type zeolite, was dealuminated using HCl solutions of increasing concentration (0.05-11.5 M). The samples were characterized by XRD, sorption of nitrogen, TPD of ammonia, FT IR and NMR spectroscopies. The preparations modified under mild conditions (acid concentration, temperature of dealumination) retained largely their crystallinity and acidity, and were active in the liquid phase isomerization of alpha-pinene. Upon more severe treatments, the samples became partially amorphous and lost their catalytic activity. The kinetics of alpha-pinene isomerization was studied over the most active catalysts. The reaction rate constants and apparent energies of activation were obtained. Initial reaction rates over the clinoptilolite type catalysts were compared with other acidic catalysts, including ferrierite-type zeolites. (C) 2015 Elsevier B.V. All rights reserved.