Abstract—Compositions and morphologies of dolomites, breunnerites, Ca‐carbonates, Ca‐sulfates and Mg, Ni, Na‐sulfates, and their petrologic interrelations, in four CI chondrites are consistent with their having been formed by aqueous activity on the CI parent body. Radiochronometric data indicate that this activity took place very early in Solar‐System history. No evidence for original (“primitive”) condensates seems to be present. However, alteration apparently took place without change in bulk meteorit