The mineral krautite (MnHAsO4 · H2O) has acidic layers and intercalates alkylamines directly by an acid-base reaction. Intercalation causes expansion of the lattice in the b direction only with a corresponding increase in basal spacing. For alkyl chains of three to eight C, ordered aggregates of alkylammonium ions are formed, which are arranged in bilayers and tilted at ~64° to the basal plane. An odd-even alternation in basal spacing indicates that the N-C1 bond is almost normal to the basal plane and H bonding between two or more H atoms of NH3 and surface O may occur. For alkylammonium ions containing more than eight C, the cations appear to form kink structures in which the alkyl chains are bent. Interstratified structures are also discussed.