Four kinds of OH groups (3740,3720,3680 and 3460 cm–1) are present in H-boralites. The 3740 and 3720 cm–1 OH groups were previously assigned to silanol, Si—OH, and acidic B⋯HO—Si groups. The results obtained in the present study suggest that both 3680 and 3460 cm–1 OH groups were formed by the hydrolysis of B—O—Si bond upon ionic exchange in an acidic NH4Cl solution. The broad 3460 cm–1 band was attributed to O⋯H—O—Si groups forming the hydrogen bond,m and the 3680 cm–1 band to B—OH groups in [graphic omitted] fragments. The OH groups in these fragments are unstable and prone to dehydroxylation.