In this study, some boron mineral samples (howlite, ulexite and tunellite) have been analysed by DTA and TG methods. The thermochemical reactions of these boron compounds have been studied. The dehydration kinetic parameters for howlite, ulexite and tunellite were activation energies: 65.0, 39.5 and 50.4 kJ mol(-1); the pre-exponential factors: 50.8 x 10(5), 6.60 x 10(5), 32.4 x 10(5) s(-1) and rate constants: 70.1, 113.1 and 82.3 s(-1), respectively, at a constant heating rate of 10 K min(-1). The average particle size was 200 mu m for all samples. The order of dehydration reactions (n) was accepted as first order. (C) 1999 Elsevier Science B.V. All rights reserved.