The role of membrane formation, diffusion, and segregated reaction in determining the composition and morphology of copper, magnesium, and zinc carbonate and nitrate precipitates has been investigated. Photography of the coalescence of drops of divalent nitrate solutions into a shallow pool of sodium carbonate, at millisecond intervals, shows the formation of lamellae of fixed diameter comprised of a network of membranes separating the solutions. Segregated reaction within a lamella yields basic nitrates internally and mainly basic carbonates externally. On the macroscopic scale, with stirring, the precipitates are gels and, as precipitated, have been investigated by chemical analysis, IR spectroscopy, and microscopy through narrow pH ranges. Such gels are complexes of water, sodium carbonate, and metal basic carbonates corresponding to typical alkali complex carbonates, NamM(CO3)((n+0.5m))(OH)((2-2n)) (m and n are the ratios of sodium and carbonate ions with respect to divalent cations), together with basic nitrates. Hydrolysis during washing changes the composition and yields basic carbonates having low values of n as reported hitherto.