The strongly coupled dusty plasmas are formed by suspending negatively charged SiO2 fine particles with 10 mum diameter in weakly ionized rf Ar discharges. The Coulomb crystals and liquids are directly observed for the first time using an optical microscope. By properly controlling the system parameters, hexagonal, fcc, and bcc crystal structures and solids with coexisting different crystal structures can be formed. Increasing the rf power causes the transition to the more disordered liquid state.
