Novel rod-shaped calcite crystals are formed by precipitation from CTAB/1-pentanol/cyclohexane microemulsions containing calcium chloride and ammonium carbonate. The calcium carbonate initially precipitates as hexagon-shaped vaterite crystals. The vaterite crystals transform to unusual rod-shaped calcite crystals over several days. The rod-shaped calcite crystals are prismatic with the longest crystal axis displaying (110) crystal faces. A possible mechanism of crystal growth is discussed. The crystals can be coated with a shell of silica or titania, and the calcite core can be removed by acid solution to leave hollow nanotubes of silica or titania. The elongated shape of the crystals and nanotubes facilitates assembly into hierarchical structures. The particles and nanotubes can be aligned by an applied electric field, and can be used to fabricate anisotropic composite membranes.