Disorder in frustrated quantum systems can critically influence their magnetic ground states and drive exotic correlated behavior. In the 𝑆=½ system ktenasite, Cu2.7⁢Zn2.3⁢(SO4)2⁢(OH)6·6⁢H2⁡O, we show that structural disorder drives an unexpected dimensional crossover and stabilizes a rare coexistence of distinct magnetic states. Neutron diffraction reveals significant Cu/Zn mixing at the Cu2 site, which tunes the Cu2+ sublattice from a two-dimensional scalene-distorted triangular lattice into a one-dimensional spin-chain network. Magnetic susceptibility, neutron diffraction, ac susceptibility, and specific heat measurements collectively indicate magnetic duality: a coexistence of incommensurate long-range magnetic order below 𝑇N=4 K and a cluster spin-glass state with 𝑇f=3.28 K at 𝜈=10 Hz. Our findings highlight ktenasite as a rare platform where structural disorder tunes the effective dimensionality and stabilizes coexisting ordered and glassy magnetic phases, offering a unique opportunity to explore the interplay of frustration, disorder, and dimensional crossover in quantum magnets.