The layered minerals brucite Mg(OH)(2) and portlandite Ca(OH)(2) are investigated at the ab initio quantum mechanical level, by using the periodic CRYSTAL 98 program and an all-electron Gaussian-type basis set. The equilibrium lattice parameters, lattice formation and hydration energies (with respect to the MO + H2O - M(OH), reaction, where M = Mg, Ca) and the Raman O-H vibrational frequencies have been evaluated. The calculations have been performed at the Hartree-Fock (HF), density functional theory (DFT) and hybrid (B3LYP) levels. As regards DFT, the local density (LDA) and generalized gradient (GGA) approximations have been used. Excellent agreement between calculated and experimental lattice and hydration energies and Raman frequencies has been found with the B3LYP approximation.