Two new dimorphic spin-1/2 quantum magnets, α- and β-Cu4O2(VO4)Cl, were synthesized via a chemical vapor transport method that emulates mineral formation in volcanic fumaroles. α-Cu4O2(VO4)Cl (1) is a pure vanadate analogue of the coparsite mineral characterized by [O2Cu4]4+ 1D single rods, whereas β-Cu4O2(VO4)Cl (2) adopts a new structure type with the [O2Cu4]4+ 2D layered topology. The thermal expansions of both 1 and 2 studied by high-temperature single-crystal X-ray diffraction are reported. Using ab initio calculations, we infer the presence of antiferromagnetic Cu1-Cu3 units with strong couplings on the order of 200-400 K forming chains (1) and layers (2). The Cu2 atoms are weakly coupled to such units. Magnetic susceptibility measurements corroborate this scenario by showing deviations from the paramagnetic behavior even at 300 K. Moreover, 1 reveals an antiferromagnetic ordering below TN = 24 K with a weak uncompensated magnetic moment.