Dark Gray Luvisols developed from dune sand parent material near Devon, Alberta, have Ae horizons of unusually high chromas and dark values when moist, and B horizons with very hard massive structure when dry. Micromorphological examination shows the high chromas in the Ae reflect the presence of organic, and to a lesser extent, matrix coatings on f-members. Hardening results from development of chlamydic and plectic fabrics in the B, where clay bridges bind f-members together. The illuvial clays contributing to the fabric organization are, in part, derived from accretionary eolian deposits (containing minerals such as beidellite), in part from calcitic residua (largely non-expandable components), and in part from dislodgement of clay domains (rich in montmorillonite) inherent within the Ae horizon as a constituent of the original parent material. All are actively translocated down the solum.