A process is provided for the selective adsorption of one or more minor constituents from a bulk gas stream using a chabazite in which the bulk gas is size excluded from the pore structure of the chabazite or the minor constituent to be separated has a heat of adsorption greater than that of the bulk gas and the process is carried out under conditions such that the partial pressure of the minor constituent is in the linear low pressure region of the isotherm for the minor constituent and the adsorbent is a dehydrated divalent cation-containing chabazite having a Si/Al ratio of 1.8 to 2.7, a cation sitting, f.sub.s, of 0.7 to 1, and a cation distribution, f.sub.d, of 0.62 to 1.