Chemical weathering of granite proceeds through a predictable sequence on an Al2O3-(CaO+Na2O)-K2O ternary diagram: the fresh rock composition plots near the base of the triangle (dominated by feldspar-derived CaO, Na2O, and K2O), and as weathering progresses, the most mobile, soluble cations (Ca2+, Na+, then K+) are progressively leached away in solution while relatively immobile Al2O3 becomes residually enriched, driving the weathering path from the base of the triangle upward toward the Al2O3 apex, first forming clay minerals (illite, kaolinite) at intermediate compositions and ultimately forming gibbsite (essentially pure Al2O3) as the terminal weathering residue.