The decrepitation properties of the two typical boron minerals colemanite and ulexite reveal that, whereas colemanite undergoes decrepitation, ulexite shows no sign of significant fragmentation upon heating. This process enables separation of colemanite from ulexite at temperatures above 400 degrees C. A thermodynamic evaluation of 14 boron minerals has shown that only colemanite exhibits decrepitation. A mechanism involving the temperature differential at the onset of dehydration and decomposition and the resultant enthalpy change is proposed as being responsible for this intriguing phenomenon.