Crystallization of concentrated colloidal suspensions was studied in real space using laser scanning confocal microscopy. Direct imaging in three dimensions allowed identification and observation of nucleation and growth of crystalline regions, providing the first experimental measure of properties of the nucleating crystallites. By following their evolution, critical nuclei were identified, nucleation rates were determined, and the average surface tension of the crystal-liquid interface was measured. The structure of the nuclei was the same as the bulk solid phase, random-hexagonal-close-packed (rhcp), and their average shape was rather aspherical, with rough rather than faceted surfaces.